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Vietnam War casualties
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The American War Memorial of the dead Vietnamese soldiers, Vietnam (Hanoi).
The Vietnam Veterans Memorial, USA (Washington, D.C.).
Two major war memorials commemorating the dead soldiers in. the Second Indochina War (a.k.a. the Vietnam War and the American War).
Estimates of casualties of the Vietnam War vary widely. Estimates include both civilian and military deaths in North and South Vietnam, Laos, and Cambodia.
The conflict persisted from 1955 to 1975 and most of the fighting took place in South Vietnam; accordingly it suffered the most casualties. The war also spilled over into the neighboring countries of Cambodia and Laos which also endured casualties from aerial and ground fighting.
Civilian deaths caused by both sides amounted to a significant percentage of total deaths. Civilian deaths were partly caused by assassinations, massacres and terror tactics. Civilian deaths were also caused by mortar and artillery, extensive aerial bombing and the use of firepower in military operations conducted in heavily populated areas. Some 365,000 Vietnamese civilians are estimated by one source to have died as a result of the war during the period of American involvement.[1]
A number of incidents occurred during the war in which civilians were deliberately targeted or killed. The best-known are the Massacre at Huế and the My Lai massacre.
Contents
1 Total number of deaths
2 Civilian deaths in the Vietnam War
2.1 Deaths caused by North Vietnam/VC forces
2.2 Deaths caused by South Vietnam
2.3 Deaths caused by the American military
2.4 Deaths caused by the South Korean military
3 Army of the Republic of Vietnam
4 North Vietnamese and Viet Cong military deaths
5 United States armed forces
5.1 Disproportion of African American casualties
6 Specific incidents
7 Aftereffects
8 Other nations' casualties
8.1 Military
9 References
10 External links
Total number of deaths[edit]
Waiting to Lift Off by James Pollock, Vietnam Combat Artists Program, CAT IV, 1967. Courtesy of National Museum of the U.S. Army
Estimates of the total number of deaths in the Vietnam War vary widely. The wide disparity among the estimates cited below is partially explained by the different time periods of the Vietnam War covered by the studies and whether casualties in Cambodia and Laos were included in the estimates.
Guenter Lewy in 1978 estimated 1,353,000 total deaths in North and South Vietnam during the period 1965–1974 in which the U.S. was most engaged in the war. Lewy reduced the number of VC and PAVN battle deaths claimed by the U.S. by 30 percent (in accordance with the opinion of United States Department of Defense officials), and assumed that one third of the battle deaths of the PAVN/VC were actually civilians. His estimate of total deaths is reflected in the table.[2]
Deaths in Vietnam War (1965–1974) per Guenter Lewy
Allied military deaths
282,000
NVA/VC military deaths
444,000
Civilian deaths (North and South Vietnam)
627,000
Total deaths
1,353,000

A 1995 demographic study in Population and Development Review calculated 791,000–1,141,000 war-related Vietnamese deaths, both soldiers and civilians, for all of Vietnam from 1965–75. The study came up with a most likely Vietnamese death toll of 882,000, which included 655,000 adult males (above 15 years of age), 143,000 adult females, and 84,000 children. Those totals include only Vietnamese deaths, and do not include American and other allied military deaths which amounted to about 64,000.[3] The study has been criticized for its small sample size, the imbalance in the sample between rural and urban areas, and the possible overlooking of clusters of high mortality rates.[4]
In 1995, the Vietnamese government released its estimate of war deaths for the more lengthy period of 1955–75. PAVN and VC deaths were reported as 1.1 million and civilian deaths of Vietnamese on both sides totaled 2.0 million. These estimates probably include deaths of Vietnamese soldiers in Laos and Cambodia, but do not include deaths of South Vietnamese and allied soldiers which would add nearly 300,000 for a grand total of 3.4 million military and civilian dead.[5]
A 2008 study by the BMJ (formerly British Medical Journal) came up with a higher toll of 3,812,000 dead in Vietnam between 1955–2002. For the period of the Vietnam War the totals are 1,310,000 between 1955 and 1964, 1,700,000 between 1965–74 and 810,000 between 1975 and 1984. (The estimates for 1955–64 are much higher than other estimates). The sum of those totals is 3,091,000 war deaths between 1955–75.[4]
Uppsala University in Sweden maintains the Armed Conflict Database. Their estimates for conflict deaths in Vietnam are 164,923 from 1955–64 and 1,458,050 from 1965–75 for a total of 1,622,973. The database also estimates combat deaths in Cambodia for the years 1967–75 to total 259,000. Data for deaths in Laos is incomplete.[6]
R. J. Rummel's mid-range estimate in 1997 was that the total deaths due to the Vietnam conflict totaled 2,450,000 from 1954–75. Rummel calculated PAVN/VC deaths at 1,062,000 and ARVN and allied war deaths of 741,000,with both totals include civilians inadvertently killed. He estimated that victims of democide (deliberate killing of civilians) included 214,000 by North Vietnam/VC and 98,000 by South Vietnam and its allies. Deaths in Cambodia and Laos were estimated at 273,000 and 62,000 respectively.[7]
Deaths in Vietnam War (1954–75) per R. J. Rummel (except where otherwise noted)[7]
Low estimate of deaths
Middle estimate of deaths
High estimate of deaths
Notes and comments
North Vietnam/Viet Cong military and civilian war dead
533,000 1,062,000 1,489,000 includes an estimated 50,000/65,000/70,000 civilians killed by U.S/SVN bombing/shelling[8]
South Vietnam/U.S./South Korea war military and civilian war dead
429,000 741,000 1,119,000 includes 360,000/391,000/720,000 civilians[9]
Democide by North Vietnam/Viet Cong
131,000 214,000 302,000 25,000/50,000/75,000 killed in North Vietnam, 106,000/164,000/227,000 killed in South Vietnam
Democide by South Vietnam
57,000 89,000 284,000 Democide is the murder of persons by or at the behest of governments.
Democide by the United States
4,000 6,000 10,000 Democide is the murder of persons by or at the behest of governments.
Democide by South Korea
3,000 3,000 3,000 Rummel does not give a medium or high estimate.
Subtotal Vietnam
1,156,000 2,115,000 3,207,000
Cambodians
273,000 273,000 273,000 Rummel estimates 212,000 killed by Khmer Rouge (1967–1975), 60,000 killed by U.S. and 1,000 killed by South Vietnam (1967–73). No estimate given for deaths caused by Viet Cong/North Vietnam (1954–75).[10]
Laotians
28,000 62,000 115,000 Source:[4]
Grand total of war deaths: Vietnam, Cambodia, and Laos (1954–75)
1,450,000 2,450,000 3,595,000
Civilian deaths in the Vietnam War[edit]
See also: List of massacres in Vietnam
Lewy estimates that 40,000 South Vietnamese civilians were assassinated by the PAVN/VC; 250,000 were killed as a result of combat in South Vietnam, and 65,000 were killed in North Vietnam. He suggests that another 222,000 civilians were counted as military deaths by the U.S. in compiling its "body count." His estimated total of civilian deaths is 587,000.[11][12][13] It was difficult to distinguish between civilians and military personnel in many instances as many individuals were part-time guerrillas or impressed laborers who did not wear uniforms.[14][15][16]
Deaths caused by North Vietnam/VC forces[edit]
Viet Cong killed hundreds of Montagnard civilians at the village of battle of Dak Son, 1967
R. J. Rummel estimated that PAVN/VC forces killed around 164,000 civilians in democide between 1954 and 1975 in South Vietnam, from a range of between 106,000 and 227,000, plus another 50,000 killed in North Vietnam.[17] Rummel's mid-level estimate includes 17,000 South Vietnamese civil servants killed by PAVN/VC. In addition, at least 36,000 Southern civilians were executed for various reasons in the period 1967–1972.[18] About 130 American and 16,000 South Vietnamese POWs died in captivity.[19] During the peak war years, another scholar Guenter Lewy attributed almost a third of civilian deaths to the VC.[20]
Thomas Thayer in 1985 estimated that during the 1965-72 period the VC killed 33,052 South Vietnamese village officials and civil servants.[21]
Deaths caused by South Vietnam[edit]
According to RJ Rummel, from 1964 to 1975, an estimated 1,500 people died during the forced relocations of 1,200,000 civilians, another 5,000 prisoners died from ill-treatment and about 30,000 suspected communists and fighters were executed. In Quảng Nam Province 4,700 civilians were killed in 1969. This totals, from a range of between 16,000 and 167,000 deaths caused by South Vietnam during the (Diệm-era), and 42,000 and 118,000 deaths caused by South Vietnam in the post Diệm-era), excluding PAVN forces killed by the ARVN in combat.[22] Operating under the direction of the CIA and other US and South Vietnamese Intel organizations and carried out by RVN units alongside US advisers was the Phoenix Program, intended to neutralise the VC political infrastructure, whom were the civilian administration of the Viet Cong/Provisional Revolutionary Government via infiltration, capture, counter-terrorism, interrogation, and assassination.[23] The program resulted in an estimated 26,000 to 41,000 killed, with an unknown number possibly being innocent civilians.[23]
Deaths caused by the American military[edit]
RJ Rummel estimated that American forces committed around 5,500 intentional democidal mass-killings between 1960 and 1972, from a range of between 4,000 and 10,000 killed in democide.[24] Benjamin Valentino attributes possibly 110,000–310,000 "counterguerrilla mass killings" to U.S. and South Vietnamese forces during the war.[25]
Estimates for the number of North Vietnamese civilian deaths resulting from US bombing range from 30,000–65,000.[26][3] Higher estimates place the number of civilian deaths caused by American bombing of North Vietnam in Operation Rolling Thunder at 182,000.[27] American bombing in Cambodia is estimated to have killed between 30,000 and 150,000 civilians and combatants.[25][28]
Burial of 300 unidentified victims from the Huế Massacre, killed by communist forces and found after the ARVN and U.S. Marines retook the area in March, 1968. U.S. Military photo[29][30]
18.2 million gallons of Agent Orange, some of which was contaminated with Dioxin, was sprayed by the U.S. military over more than 10% of Southern Vietnam,[31] as part of the U.S. herbicidal warfare program, Operation Ranch Hand, during the Vietnam War from 1961 to 1971. Vietnam's government claimed that 400,000 people were killed or maimed as a result of after effects, and that 500,000 children were born with birth defects.[32] The United States government has challenged these figures as being unreliable.[33]
Guenter Lewy estimates that around 220,000 civilians in South Vietnam were killed in US, ARVN and other allied land operations and miscounted as "enemy KIA".[34] For official US military operations reports, there are no established distinctions between enemy KIA and civilian KIA, since body counts was a direct measure of operational success often caused US "operations reports" to list civilians killed as enemy KIA.[35] The pressure to produce body counts as a measure of operational success often caused US "operations reports" to list civilians killed as enemy KIA[36] with one prominent example being the My Lai Massacre written off as an operational success.[37][38] It was assumed by US forces that, were an area is declared a free-fire zone that all individuals killed regardless of whether they were combatants or not, were considered enemy KIA.[39] This it is suggested explains the discrepancies between recovered weapons and body-count figures, alongside inflation.[34] Official operations reports rarely made a distinction between civilians killed and actual combatants, drastically inflating the numbers of "enemies killed" as it was directly tied to promotions and commendation.[40][38] At other times US-committed atrocities were often tied to or blamed on the NVA/VC to skirt punishment.[40] There are further claims made that when air-strikes or artillery were called in on villages, usually civilian casualties were reported as "enemies killed".[40][38] An alleged massacre in which the killed was reported as "enemy KIA" was the Thuy Bo massacre.
German historian Bernd Greiner mentions the following war crimes reported, and/or investigated by the Peers Commission and the Vietnam War Crimes Working Group, among other sources:[41]
Seven massacres officially confirmed by the American side. My Lai (4) and My Khe (4) claimed the largest number of victims with 420 and 90 respectively, and in five other places altogether about 100 civilians were executed. The My Lai Massacre, where civilians killed were described as enemy combatants, was initially reported as a battlefield victory.[42] This was especially true when areas would be declare a free-fire zone. Victories were often based on body-counts, which resulted in further distortions of actual combatant deaths.[43]
Two further massacres were reported by soldiers who had taken part in them, one north of Đức Pho in Quảng Ngãi Province in the summer of 1968 (14 victims), another in Bình Định Province on 20 July 1969 (25 victims).
Tiger Force, a special operations force, murdered hundreds, possibly over a thousand, civilians.
In the course of large-scale operations an unknown number of non-combatants were killed either accidentally or deliberately – with the Army Inspector General estimating that more than 5,000 died in the course of Operation Speedy Express. Excluding deaths from artillery and air attacks, the total number of dead may have reached tens of thousands during the entire war.
According to the Information Bureau of the Provisional Revolutionary Government of South Vietnam (PRG), between April 1968 and the end of 1970 American ground troops killed about 6,500 civilians in the course of twenty-one operations either on their own or alongside their allies. Three of the massacres reported on the American side were not mentioned on the PRG list.
Nick Turse, in his 2013 book, Kill Anything that Moves, argues that a relentless drive toward higher body counts, a widespread use of free-fire zones, rules of engagement where civilians who ran from soldiers or helicopters could be viewed as VC, and a widespread disdain for Vietnamese civilians led to massive civilian casualties and endemic war crimes inflicted by U.S. troops.[44] One example cited by Turse is Operation Speedy Express, an operation by the 9th Infantry Division, which was described by John Paul Vann as, in effect, "many My Lais".[44]
Air force captain, Brian Wilson, who carried out bomb-damage assessments in free-fire zones throughout the delta, saw the results firsthand. "It was the epitome of immorality...One of the times I counted bodies after an air strike—which always ended with two napalm bombs which would just fry everything that was left—I counted sixty-two bodies. In my report I described them as so many women between fifteen and twenty-five and so many children—usually in their mothers' arms or very close to them—and so many old people." When he later read the official tally of dead, he found that it listed them as 130 VC killed.[45]
Deaths caused by the South Korean military[edit]
United States Marine recovered victim's bodies who were killed by Korean Marines in Phong Nhi and Phong Nhat hamlets on February 12, 1968.[46]
2nd Marine Brigade reportedly conducted the Binh Tai Massacre on 9 October 1966.[47] In December 1966, the Blue Dragon Brigade reportedly conducted the Bình Hòa massacre.[48] In addition is the Bình An/Tây Vinh massacre. The Second Marine Brigade conducted the Phong Nhị and Phong Nhất massacre on 12 February 1968.[49][50] South Korean Marines purportedly conducted the Hà My massacre on 25 February 1968.[51] According to a study conducted in 1968 by a Quaker-funded Vietnamese-speaking American couple, Diane and Michael Jones, there were at least 12 mass-killings conducted by South Korean forces which approached the scale of the My Lai Massacre with reports of thousands of routine murders on civilians primarily the elderly, women and children.[52][53] A separate study by a RAND Corporation employee Terry Rambo conducted interviews in 1970 in ARVN/civilian areas on reported Korean atrocities.[54] Widespread reports of deliberate mass-killings were reported to have occurred, alleging that these were systemic, deliberate policies to massacre civilians with murders running into the hundreds.[54] These policies are also reported by US commanders, with one US Marine General stating "whenever the Korean marines received fire "or think (they got) fired on from a village ... they'd divert from their march and go over and completely level the village ... it would be a lesson to (the Vietnamese)."[55] Another Marine commander Gen. Robert E. Cushman Jr. added, "we had a big problem with atrocities attributed to them, which I sent on down to Saigon." [55] Investigations by Korean civic groups have alleged there were at-least 9000 civilian massacres committed by ROK forces.[56]
Army of the Republic of Vietnam[edit]
The ARVN suffered 254,256 recorded combat deaths between 1960 and 1974, with the highest number of recorded deaths being in 1972, with 39,587 combat deaths.[57] According to Guenter Lewy, the ARVN suffered between 171,331 and 220,357 deaths during the war.[11][21]:106 R.J. Rummel estimated that ARVN lost between 219,000 and 313,000 deaths during the war including in 1975 and prior to 1960.[17]
Year
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
Total (1960-1974)
ARVN combat deaths[58] 2,223 4,004 4,457 5,665 7,457 11,242 11,953 12,716 27,915 21,833 23,346 22,738 39,587 27,901 31,219 254,256
North Vietnamese and Viet Cong military deaths[edit]
RJ Rummel estimates 1,011,000 PAVN/VC combatant deaths.[59] The official US Department of Defense figure was 950,765 communist forces killed in Vietnam from 1965 to 1974. Defense Department officials believed that these body count figures need to be deflated by 30 percent. For this figure, Guenter Lewy assumes that one-third of the reported enemy killed may have been civilians, concluding that the actual number of deaths of the VC and PAVN military forces was probably closer to 444,000.[11]
According to the Vietnamese government's national survey and assessment of war casualties, there were 849,018 PAVN/VC military personnel dead or missing, including combat death and non-combat death, from the period between 1955 and 1975. It is unclear whether or not this figure includes the 300-330,000 PAVN/VC missing in action.[60] One third of the deaths of the VC/NVA were non-combat deaths.[60] Across all three wars including the First Indochina War and the Third Indochina War there was a total of 1,146,250 military deaths: 191,605 in the First Indochina War, 849,018 in the Second Indochina War (Vietnam War), and 105,627 in the Third Indochina War.[60]
The Phoenix Program, a counterinsurgency program executed by the United States Central Intelligence Agency (CIA), United States special operations forces, and the Republic of Vietnam's security apparatus, killed 26,369 suspected of being VC operatives and informants.[61][62]
Historian Christian Appy states "search and destroy was the principal tactic; and the enemy body count was the primary measure of progress" in the US strategy of attrition. Search and destroy was a term to describe operations aimed at flushing the Viet Cong out of hiding, while body count was the measuring stick for operation success. Competitions were held between units for the highest number of Vietnamese killed. U.S. Army and marine officers knew that promotions were largely based on confirmed kills. The pressure to produce confirmed kills resulted in massive fraud. One of the most thorough studies found that American commanders exaggerated body counts by 100 percent. Furthermore there was little distinction made between armed combatants, neutral civilians and unarmed individuals for "enemy KIA".[63]
Author Mark Woodruff noted that when the Vietnamese Government finally revealed its actual losses in April 1995 as being 1.1 million dead, US body count figures had actually .[64]
United States armed forces[edit]
Casualties as of 31 May 2018:
58,318 KIA or non-combat deaths (including the missing & deaths in captivity)[65]
153,303 WIA (excluding 150,332 persons not requiring hospital care)[66]
1,597 MIA (originally 2,646)[67]
766–778 POW (652–662 freed/escaped*,[68][69] 114–116 died in captivity)[68][70]
Note: *One escapee died of wounds sustained during his rescue 15 days later.[71]
During the Vietnam War, 30% of wounded service members died of their wounds.[72] 30-35% of American deaths in the war were non-combat or friendly fire deaths; the largest causes of death in the U.S. armed forces were small arms fire (31.8%), booby traps including mines and frags (27.4%), and aircraft crashes (14.7%).[73]
Disproportion of African American casualties[edit]
Blacks suffered disproportionately high casualty rates in Vietnam. In 1965 alone they comprised almost one out of every four combat deaths.[74][75] With the draft increasing due to the troop buildup in South Vietnam, the military significantly lowered its admission standards. In October 1966, Defense Secretary Robert McNamara initiated Project 100,000 which further lowered military standards for 100,000 additional draftees per year. McNamara claimed this program would provide valuable training, skills and opportunity to America's poor – a promise that was never carried out. Many black men who had previously been ineligible could now be drafted, along with many poor and racially intolerant white men from the southern states.[76][77] The number of US military personnel in Vietnam jumped from 23,300 in 1965 to 465,600 by the end of 1967. Between October 1966 and June 1969, 246,000 soldiers were recruited through Project 100,000, of whom 41% were black, while blacks only made up about 11% of the population of the US.[76] Of the 27 million draft-age men between 1964 and 1973, 40% were drafted into military service, and only 10% were actually sent to Vietnam. This group was made up almost entirely of either work-class or rural youth. College students who did not avoid the draft were generally sent to non-combat and service roles or made officers, while high school drop-outs and the working class were sent into combat roles. Blacks often made up a disproportionate 25% to 80% or more of combat units, while constituting only 12% of the military.[74][78]
Civil rights leaders including Martin Luther King Jr., Malcolm X, John Lewis, Muhammad Ali, and others, criticized the racial disparity in both casualties and representation in the entire military, prompting the Pentagon to order cutbacks in the number of African Americans in combat positions. Commander George L. Jackson said, "In response to this criticism, the Department of Defense took steps to readjust force levels in order to achieve an equitable proportion and employment of Negroes in Vietnam." The Army instigated myriad reforms, addressed issues of discrimination and prejudice from the post exchanges to the lack of black officers, and introduced "Mandatory Watch And Action Committees" into each unit. This resulted in a dramatic decrease in the proportion of black casualties, and by late 1967, black casualties had fallen to 13%, and were below 10% in 1970 to 1972.[76][79] As a result, by the war's completion, total black casualties averaged 12.5% of US combat deaths, approximately equal to percentage of draft-eligible black men, though still slightly higher than the 10% who served in the military.[79]
Specific incidents[edit]
Vietnamese women and children in Mỹ Lai before being killed in the massacre, March 16, 1968.[80] They were killed seconds after the photo was taken.[81] Photo by Ronald L. Haeberle
2,800–6,000 civilians were reportedly killed by the PAVN/VC forces in the Massacre at Huế throughout February 1968.[82]
66 civilians were reportedly killed by South Korean forces in Binh Tai Massacre on October 9, 1966.[83]
1,004 to 1,2000 civilians were reportedly killed by South Korean forces in the Bình An/Tây Vinh massacre[84].
430 civilians were reportedly killed by South Korean forces in Bình Hòa massacre between December 3 and December 6, 1966.[48]
79 civilians were killed by South Korean forces in Phong Nhị and Phong Nhất massacre massacre on 12 February 1968.
135 civilians were reportedly killed by South Korean forces in Hà My massacre on 25 February 1968.
More than 500 civilians were killed by the US Army during the My Lai Massacre on 16 March 1968.[80][85]
19 civilians killed by US forces 8 February 1968 in Quảng Nam Province.[86]
80–90 civilians killed by US forces 16 March 1968, at My Khe.[87]
A Newsweek journalist claimed an unnamed official told him that an estimated 5,000 civilians died as "collateral damage" from the American military during Operation Speedy Express.[88]
Almost 252 Degar civilians were killed by the VC in the Đắk Sơn massacre on 5 December 1967.[89]
More than 25,000 South Vietnamese civilians were killed and almost a million become temporary refugees, with over 600,000 interned in South Vietnamese Government camps as a result of North Vietnam's 1972 Easter Offensive.[90]
At least 81 civilians were killed by Tiger Force in the Song Ve Valley during Operation Wheeler/Wallowa.[91]
Aftereffects[edit]
Unexploded ordnance especially bombs dropped by the United States, continue to detonate and kill people today. The Vietnamese government claims that unexploded ordnance has killed some 42,000 people since the war officially ended.[92][93] In 2012 alone, unexploded bombs and other ordnance claimed 500 casualties in Vietnam, Laos and Cambodia, according to activists and government databases. The United States has spent over $65 million since 1998 in an attempt to make Vietnam safe.[94]
Agent Orange and similar chemical substances, have also caused a considerable number of deaths and injuries over the years, including the US Air Force crew that handled them. The government of Vietnam says that 4 million of its citizens were exposed to Agent Orange, and as many as 3 million have suffered illnesses because of it; these figures include the children of people who were exposed.[95] The Red Cross of Vietnam estimates that up to 1 million people are disabled or have health problems due to contaminated Agent Orange.[96]
On 9 August 2012, the United States and Vietnam began a cooperative cleaning up of the toxic chemical on part of Da Nang International Airport, marking the first time Washington has been involved in cleaning up Agent Orange in Vietnam. Da Nang was the primary storage site of the chemical. Two other cleanup sites the United States and Vietnam are looking at is Biên Hòa Air Base, in the southern province of Đồng Nai – a 'hotspot' for dioxin – and Phù Cát Air Base in Bình Định Province, says U.S. Ambassador to Vietnam David Shear. According to the Vietnamese newspaper Nhân Dân, the U.S. government is providing $41 million to the project, which will reduce the contamination level in 73,000 m3 of soil by late 2016.[97]
Other nations' casualties[edit]
Cambodian Civil War
275,000–310,000 killed[98][99][100]
Laotian Civil War
20,000–62,000 killed[4]
Military[edit]
South Korea
5,099 Killed in action
14,232 wounded
4 missing in action[101]
Australia
426 killed in action, 74 died of other causes[102]
3,129 wounded[102]
6 missing in action (all accounted for and repatriated)[103]
Thailand
351 killed in action[101][104]
1,358 wounded
New Zealand
37 killed in action + 2 Civilians[105][106]
187 wounded
Philippines
9 killed in action[107]
64 wounded[107]
Republic Of China (Taiwan)
25 killed in action
People's Republic Of China
1,446 killed in action[108]
Soviet Union
~16.[109]
Great Britain
~1.[110]
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Jump up ^ "Body Count in Vietnam | HistoryNet". www.historynet.com. Retrieved 2018-06-03.
Jump up ^ http://ls-tlss.ucl.ac.uk/course-materials/POLS6016_65225
^ Jump up to: a b c Appy, Christian (1993). Working-Class War: American Combat Soldiers and Vietnam. http://projectsmrj.pbworks.com/f/Working+Class+War+-+Christian+Appy.pdf: UNC Chapel Hill. p. 273.
Jump up ^ https://thevietnamwar.info/free-fire-zone/
^ Jump up to: a b c "Declassification of the BDM Study, "The Strategic Lessons Learned in Vietnam"" (PDF). Defense Technical Center. p. 225-234. [dead link]
Jump up ^ Greiner, Bernd (2010). War Without Fronts: The USA in Vietnam. Yale University Press. ISBN 0300168047.
Jump up ^ http://ls-tlss.ucl.ac.uk/course-materials/POLS6016_65225
Jump up ^ "'Anything That Moves': Civilians And The Vietnam War". www.wbur.org. Retrieved 2018-06-03.
^ Jump up to: a b Turse 2013, p. 251.
Jump up ^ Turse 2013, p. 212.
Jump up ^ Kim Chang-seok (2000-11-15). 편견인가, 꿰뚫어 본 것인가 미군 정치고문 제임스 맥의 보고서 "쿠앙남성 주둔 한국군은 무능·부패·잔혹". Hankyoreh (in Korean). Retrieved 2012-10-14.
Jump up ^ Armstrong, Charles (2001). "America's Korea, Korea's Vietnam". Critical Asian Studies. Routledge. 33 (4): 530.
^ Jump up to: a b "On War extra – Vietnam's massacre survivors". Al Jazeera. 2009-01-04. Retrieved 2012-10-14.
Jump up ^ Go Gyeong-tae (2001-04-24). 특집 "그날의 주검을 어찌 잊으랴" 베트남전 종전 26돌, 퐁니·퐁넛촌의 참화를 전하는 사진을 들고 현장에 가다. Hankyoreh (in Korean). Retrieved 2012-10-14.
Jump up ^ 여기 한 충격적인 보고서가 있다 미국이 기록한 한국군의 베트남 학살 보고서 발견. Ohmynews (in Korean). 2000-11-14. Retrieved 2012-10-14.
Jump up ^ Kwon, Heonik. After the massacre: commemoration and consolation in Ha My and My Lai. University of California Press. p. 2. ISBN 9780520247970.
Jump up ^ Chomsky, Noam; Herman, Edward (1973). Counter-Revolutionary Violence:Bloodbaths in fact and propaganda (PDF). Warner Modular Publications.
Jump up ^ Journal, The Asia Pacific. "Anatomy of US and South Korean Massacres in the Vietnamese Year of the Monkey, 1968 | The Asia-Pacific Journal: Japan Focus". apjjf.org. Retrieved 2018-05-12.
^ Jump up to: a b https://www.nytimes.com/1970/01/10/archives/vietnam-killings-laid-to-koreans-researcher-says-he-found-evidence.html
^ Jump up to: a b CNN, James Griffiths,. "The 'forgotten' My Lai: South Korea's Vietnam War massacres". CNN. Retrieved 2018-05-27.
Jump up ^ "Citizens' court to investigate Vietnam War atrocities committed by South Korean troops". Retrieved 2018-06-03.
Jump up ^ Clarke, Jeffrey J. (1988), United States Army in Vietnam: Advice and Support: The Final Years, 1965–1973, Washington, D.C: Center of Military History, United States Army, p. 275
Jump up ^ Clarke, Jeffrey J. (1988), United States Army in Vietnam: Advice and Support: The Final Years, 1965–1973, Washington, D.C: Center of Military History, United States Army, p. 275
Jump up ^ Rummel 1997, Line 102.
^ Jump up to: a b c Chuyên đề 4 CÔNG TÁC TÌM KIẾM, QUY TẬP HÀI CỐT LIỆT SĨ TỪ NAY ĐẾN NĂM 2020 VÀ NHỮNG NĂM TIẾP THEO, datafile.chinhsachquandoi.gov.vn/Quản%20lý%20chỉ%20đạo/Chuyên%20đề%204.doc
Jump up ^ McCoy, Alfred W. (2006). A question of torture: CIA interrogation, from the Cold War to the War on Terror. Macmillan. p. 68. ISBN 978-0-8050-8041-4.
Jump up ^ Harbury, Jennifer (2005). Truth, torture, and the American way: the history and consequences of U.S. involvement in torture. Beacon Press. p. 97. ISBN 978-0-8070-0307-7.
Jump up ^ Appy, Christian G. (2000). Working-Class War: American Combat Soldiers and Vietnam. Univ of North Carolina Press. p. 153-156.
Jump up ^ Woodruff, Mark (1999). Unheralded Victory: Who won the Vietnam war?. Harper Collins. p. 211. ISBN 0004725190.
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^ Jump up to: a b Vietnam War Statistics
Jump up ^ [1] [2]
Jump up ^ American Vietnam War Casualty Statistics
Jump up ^ Vietnam Prisoners of War – Escapes and Attempts
Jump up ^ Scott McGaugh (16 September 2012). "Learning from America's Wars, Past and Present U.S. Battlefield Medicine Has Come a Long Way, from Antietam to Iraq". San Diego Union Tribune. Archived from the original on 27 July 2014. Retrieved 22 February 2013.
Jump up ^ The American War Library. [www.americanwarlibrary.com/vietnam/vwc1.htm Vietnam War Casualties and Cause.] Data compiled William F. Abbott from figures obtained shortly after the construction of the Vietnam War Memorial.
^ Jump up to: a b Fighting on Two Fronts: African Americans and the Vietnam War; Westheider, James E.; New York University Press; 1997; pgs. 11–16
Jump up ^ African-Americans In Combat
^ Jump up to: a b c War within war; The Guardian; September 14, 2001; James Maycock
Jump up ^ Working-Class War: American Combat Soldiers & Vietnam; Appy, Christian; University of North Carolina Press; 2003; pgs. 31–33
Jump up ^ Vietnam: The Soldier's Revolt
^ Jump up to: a b Working-Class War: American Combat Soldiers and Vietnam: American Combat
^ Jump up to: a b "Report of the Department of Army review of the preliminary investigations into the Mỹ Lai incident. Volume III, Exhibits, Book 6—Photographs, 14 March 1970". From the Library of Congress, Military Legal Resources.[3]
Jump up ^ "My Lai", Original broadcast PBS American Experience, 9 pm, April 26, 2010 Time Index 00:35' into the first hour (no commercials)
Jump up ^ Anderson, David L. The Columbia Guide to the Vietnam War. 2004, page 98-9
Jump up ^ Armstrong, Charles (2001). Critical asian studies, Volume 33, Issue 4 Page 530: "America's Korea, Korea's Vietnam".
Jump up ^ "Vietnam memorial recalls massacre by Korean troops". Retrieved 2018-06-10.
Jump up ^ BBC News Murder in the name of war – My Lai 20 July 1998 Retrieved 25/09/12
Jump up ^ LA Times "Civilian Killings Went Unpunished" August 6, 2006 Retrieved 26/09/12
Jump up ^ LA Times "Verified Civilian Slayings" August 6, 2006 Retrieved 26/09/12
Jump up ^ Kevin Buckley, "Pacification's Deadly Price", Newsweek 1972.
Jump up ^ Time "Đắk Sơn Massacre" Dec. 15, 1967
Jump up ^ Andrade, p. 529.
Jump up ^ Toledo Blade "Rogue GIs unleashed wave of terror in Central Highlands" 10/19/2003, Retrieved 23/09/12
Jump up ^ "Vietnam War Bomb Explodes Killing Four Children". Huffington Post. 3 December 2012.
Jump up ^ Vietnam war shell explodes, kills two fishermen The Australian (April 28, 2011)
Jump up ^ "Vietnam War Bombs Still Killing People 40 Years Later". The Huffington Post. 2013-08-14.
Jump up ^ Ben Stocking for AP, published in the Seattle Times May 22, 2010 [seattletimes.com/html/health/2011928849_apasvietnamusagentorange.html Vietnam, US still in conflict over Agent Orange]
Jump up ^ Jessica King (2012-08-10). "U.S. in first effort to clean up Agent Orange in Vietnam". CNN. Retrieved 2012-08-11.
Jump up ^ "U.S. starts its first Agent Orange cleanup in Vietnam". Reuters. August 9, 2012.
Jump up ^ Heuveline, Patrick (2001). "The Demographic Analysis of Mortality in Cambodia". Forced Migration and Mortality. National Academy Press. pp. 103–104. ISBN 9780309073349. Subsequent reevaluations of the demographic data situated the death toll for the [civil war] in the order of 300,000 or less.
Jump up ^ Banister, Judith; Johnson, E. Paige (1993). "After the Nightmare: The Population of Cambodia". Genocide and Democracy in Cambodia: The Khmer Rouge, the United Nations and the International Community. Yale University Southeast Asia Studies. p. 87. ISBN 9780938692492. An estimated 275,000 excess deaths. We have modeled the highest mortality we can justify for the early 1970s.
Jump up ^ Sliwinski, Marek (1995). Le Génocide Khmer Rouge: Une Analyse Démographique. Paris: L'Harmattan. pp. 42–43, 48. ISBN 978-2-738-43525-5. Of 310,000 estimated Cambodian Civil War deaths, Sliwinski attributes 46.3% to firearms, 31.7% to assassinations (a tactic primarily used by the Khmer Rouge), 17.1% to (mainly U.S.) bombing, and 4.9% to accidents.
^ Jump up to: a b KOREA military army official statistics, AUG 28, 2005 Archived 2011-07-22 at the Wayback Machine.
^ Jump up to: a b "Vietnam War, 1962–72 – Statistics". Australian War Memorial. 2003. Retrieved 2008-02-04.
Jump up ^ "Australian servicemen listed as missing in action in Vietnam". Australian War Memorial. Retrieved 14 February 2015.
Jump up ^ The Encyclopedia of the Vietnam War: A Political, Social, and Military History By Spencer C. Tucker "https://books.google.com/books?id=qh5lffww-KsC&lpg=PA53&dq=the%20encyclopedia%20of%20the%20vietnam%20war%20page%2064&pg=PA176&output=embed"
Jump up ^ "New Zealand Rolls Of Honour – By Conflict". Freepages.genealogy.rootsweb.ancestry.com. Retrieved 2012-09-25.
Jump up ^ "Overview of the war in Vietnam | VietnamWar.govt.nz, New Zealand and the Vietnam War". Vietnamwar.govt.nz. 1965-07-16. Archived from the original on 2013-07-26. Retrieved 2012-09-25.
^ Jump up to: a b Asian Allies in Viet-Nam
Jump up ^ Womack, Brantly (2006). China and Vietnam: The Politics of Asymmetry. Cambridge University Press. ISBN 9780521618342.
Jump up ^ James F. Dunnigan; Albert A. Nofi (2000). Dirty Little Secrets of the Vietnam War: Military Information You're Not Supposed to Know. Macmillan. ISBN 0-312-25282-X.
Jump up ^ Martin Porter. Did UK Forces (SAS) serve in Vietnam?.
External links[edit]
National Archives AAD Searchable database.
The Vietnam Center and Archive. Texas Tech University.
Vietnam War Casualties Records search by names and/or dates.
Vietnamese Casualties During the American war
Retrieved from "https://en.wikipedia.org/w/index.php?title=Vietnam_War_casualties&oldid=854221171"
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Alginic acid
From Wikipedia, the free encyclopedia
Jump to: navigation, search
Alginic acid
Names
Other names
Alginic acid, E400
Identifiers
CAS Number
9005-32-7 Y
ChemSpider
none
ECHA InfoCard 100.029.697
EC Number 232-680-1
E number E400 (thickeners, ...)
UNII
8C3Z4148WZ N
Properties
Chemical formula
(C6H8O6)n
Molar mass 10,000 – 600,000
Appearance white to yellow, fibrous powder
Density 1.601 g/cm3
Acidity (pKa) 1.5–3.5
Pharmacology
ATC code
A02BX13 (WHO)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is Y N ?)
Infobox references
Macrocystis pyrifera, the largest species of giant kelp
Alginic acid, also called algin or alginate, is an anionic polysaccharide distributed widely in the cell walls of brown algae, where through binding with water it forms a viscous gum. It is also a significant component of the biofilms produced by the bacterium Pseudomonas aeruginosa, the major pathogen in cystic fibrosis,[1] that confer it a high resistance to antibiotics[2] and killing by macrophages.[3] Its colour ranges from white to yellowish-brown. It is sold in filamentous, granular or powdered forms.
Contents
[hide]
1 Structure
2 Forms
3 Production
4 Uses
5 Alginate hydrogels
6 See also
7 References
8 External links
Structure[edit]
Alginic acid is a linear copolymer with homopolymeric blocks of (1-4)-linked β-D-mannuronate (M) and its C-5 epimer α-L-guluronate (G) residues, respectively, covalently linked together in different sequences or blocks. The monomers can appear in homopolymeric blocks of consecutive G-residues (G-blocks), consecutive M-residues (M-blocks) or alternating M and G-residues (MG-blocks).
Forms[edit]
Alginates are refined from brown seaweeds. A wide variety of brown seaweeds of the class Phaeophyceae are harvested throughout the world to be converted into the raw material commonly known as sodium alginate. Sodium alginate has a wide use across a wide variety of industries including food, textile printing and pharmaceutical. Dental impression material utilizes alginate as its means of gelling. Alginate is safe as an ingredient in manufactured foods.[4]
Seaweeds can be classified into three broad groups based on pigmentation: brown, red and green. These broad groups are the Phaeophyceae, Rhodophyceae and Chlorophyceae, respectively. Brown seaweeds are usually large, and range from the giant kelp Macrocystis pyrifera that is often 20 m long, to thick, leather-like seaweeds from 2–4 m long, to smaller species 30–60 cm long. None of the usual seaweeds for alginate production are cultivated. They cannot be grown by vegetative means, but must go through a reproductive cycle involving an alternation of generations. This makes cultivated brown seaweeds too expensive when compared to the costs of harvesting and transporting wild seaweeds. The only exception is for Laminaria japonica, which is cultivated in China for food but the surplus material is diverted to the alginate industry in China.
Alginates from different species of brown seaweed often have variations in their chemical structure, resulting in different physical properties. For example, some may yield an alginate that gives a strong gel, another a weaker gel; some may readily give a cream/white alginate, while others are difficult to gel, and are best used for technical applications where color does not matter.[5]
Commercial varieties of alginate are extracted from seaweed, including the giant kelp Macrocystis pyrifera, Ascophyllum nodosum, and various types of Laminaria. It is also produced by two bacterial genera Pseudomonas and Azotobacter, which played a major role in the unravelling of its biosynthesis pathway. Bacterial alginates are useful for the production of micro- or nanostructures suitable for medical applications.[6]
Sodium alginate is the sodium salt of alginic acid. Its empirical formula is NaC6H7O6. Sodium alginate is a gum, extracted from the cell walls of brown algae.
Potassium alginate is a chemical compound that is the potassium salt of alginic acid. It is an extract of seaweed. Its empirical chemical formula is KC6H7O6.
Calcium alginate, made from sodium alginate from which the sodium ion has been removed and replaced with calcium, has the chemical formula C12H14CaO12.
Production[edit]
The processes for the manufacture of sodium alginate from brown seaweeds fall into two categories: 1) Calcium alginate method and, 2) Alginic acid method. The chemistry of the processes used to extract sodium alginate from brown seaweeds is relatively simple. The difficulties of the processes arise from the physical separations which are required, such as the need to filter slimy residues from viscous solutions or to separate gelatinous precipitates which hold large amounts of liquid within the structure and which resist filtration and centrifugation.[7]
Uses[edit]
This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (October 2015) (Learn how and when to remove this template message)
Alginate absorbs water quickly, which makes it useful as an additive in dehydrated products such as slimming aids, and in the manufacture of paper and textiles. It is also used for waterproofing and fireproofing fabrics, in the food industry as a thickening agent for drinks, ice cream and cosmetics, and as a gelling agent for jellies.[citation needed]
Alginate is used as an ingredient in various pharmaceutical preparations, such as Gaviscon, in which it combines with bicarbonate to inhibit reflux. Sodium alginate is used as an impression-making material in dentistry, prosthetics, lifecasting and for creating positives for small-scale casting.
Sodium alginate is used in reactive dye printing and as a thickener for reactive dyes in textile screen-printing.[citation needed] Alginates do not react with these dyes and wash out easily, unlike starch-based thickeners.
As a material for micro-encapsulation.[8]
Calcium alginate is used in different types of medical products including skin wound dressings to promote healing[9] and can be removed with less pain than conventional dressings.[citation needed]
Alginate hydrogels[edit]
Alginate may be used in a hydrogel consisting of microparticles or bulk gels combined with nerve growth factor in bioengineering research to stimulate brain tissue for possible regeneration.[10] In research on bone reconstruction, alginate composites have favorable properties encouraging regeneration, such as improved porosity, cell proliferation, and mechanical strength, among other factors.[11]
See also[edit]
Hyaluronic acid: a polysaccharide in animals.
Agar
References[edit]
Jump up ^ Davies JC Pseudomonas aeruginosa in cystic fibrosis: pathogenesis and persistence. Paediatr Respir Rev. 2002 Jun;3(2):128-34. PMID 12297059
Jump up ^ Boyd A, Chakrabarty AM. Pseudomonas aeruginosa biofilms: role of the alginate exopolysaccharide. J Ind Microbiol. 1995 Sep;15(3):162-8. PMID 8519473
Jump up ^ Leid JG, et al. The exopolysaccharide alginate protects Pseudomonas aeruginosa biofilm bacteria from IFN-gamma-mediated macrophage killing. J Immunol. 2005 Dec 1;175(11):7512-8. PMID 16301659 Free full text
Jump up ^ "Alginates" (PDF). Agricultural Marketing Service, US Department of Agriculture. 5 February 2015. Retrieved 1 March 2018.
Jump up ^ FAO FISHERIES TECHNICAL PAPER 441, Tevita Bainiloga Jnr, School of Chemistry, University College, University of New South Wales and Australian Defence Force Academy Canberra Australia
Jump up ^ Remminghorst and Rehm (2009). "Microbial Production of Alginate: Biosynthesis and Applications". Microbial Production of Biopolymers and Polymer Precursors. Caister Academic Press. ISBN 978-1-904455-36-3.
Jump up ^ FAO Fisheries Technical Paper, 2003
Jump up ^ Aizpurua-Olaizola, Oier; Navarro, Patricia; Vallejo, Asier; Olivares, Maitane; Etxebarria, Nestor; Usobiaga, Aresatz (2016-01-01). "Microencapsulation and storage stability of polyphenols from Vitis vinifera grape wastes". Food Chemistry. 190: 614–621. doi:10.1016/j.foodchem.2015.05.117. PMID 26213018.
Jump up ^ Lansdown AB (2002). "Calcium: a potential central regulator in wound healing in the skin". Wound Repair Regen. 10 (5): 271–85. doi:10.1046/j.1524-475x.2002.10502.x. PMID 12406163.
Jump up ^ Büyüköz, M.; Erdal, E.; Altinkaya, S.A. (2016). "Nanofibrous gelatin scaffolds integrated with NGF-loaded alginate microspheres for brain tissue engineering". J. Tissue Eng. Regen. Med. 12 (2): e707. doi:10.1002/term.2353. PMID 27863118.
Jump up ^ Venkatesan, J; Bhatnagar, I; Manivasagan, P; Kang, K. H.; Kim, S. K. (2015). "Alginate composites for bone tissue engineering: A review". International Journal of Biological Macromolecules. 72: 269–81. doi:10.1016/j.ijbiomac.2014.07.008. PMID 25020082.
External links[edit]
Alginate seaweed sources
Alginate properties
Alginate medical uses
article Wired on Easy Cheese, describing sodium alginate
[hide]
v
t
e
Drugs for peptic ulcer and GERD/GORD (A02B)
H2 antagonists ("-tidine")
Cimetidine
Famotidine
Lafutidine
Lavoltidine (loxtidine)
Niperotidine
Nizatidine
Ranitidine
Roxatidine
Prostaglandins (E)/analogues ("-prost-")
Misoprostol
Enprostil
Proton-pump inhibitors ("-prazole")
Azeloprazole
Dexlansoprazole
Esomeprazole
Ilaprazole
Lansoprazole
Omeprazole
Pantoprazole
Picoprazole
Rabeprazole
Tenatoprazole
Timoprazole
Potassium-competitive acid blockers ("-prazan")
Linaprazan
Revaprazan
Soraprazan
Vonoprazan
Others
Aceglutamide aluminum
Acetoxolone
Alginic acid
Arbaclofen placarbil
Bismuth subcitrate
Carbenoxolone
Cetraxate
Gefarnate
Lesogaberan
Pirenzepine
Proglumide
Rebamipide
Sucralfate
Sulglicotide
Telenzepine
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Engine knocking
From Wikipedia, the free encyclopedia
Jump to navigation Jump to search
"Pinging" redirects here. For other uses, see Ping (disambiguation).
Knocking (also knock, detonation, spark knock, pinging or pinking) in spark-ignition internal combustion engines occurs when combustion of some of the air/fuel mixture in the cylinder does not result from propagation of the flame front ignited by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front.
The fuel-air charge is meant to be ignited by the spark plug only, and at a precise point in the piston's stroke. Knock occurs when the peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive.
Knocking should not be confused with pre-ignition—they are two separate events. However, pre-ignition is usually followed by knocking.
The phenomenon of detonation was first observed and described by Harry Ricardo during experiments carried out between 1916 and 1919 to discover the reason for failures in aircraft engines.[1]
Contents
1 Normal combustion
2 Abnormal combustion
3 Knock detection
4 Knock prediction
5 Knock Control
6 References
7 Further reading
8 External links
Normal combustion[edit]
Under ideal conditions the common internal combustion engine burns the fuel/air mixture in the cylinder in an orderly and controlled fashion. The combustion is started by the spark plug some 10 to 40 crankshaft degrees prior to top dead center (TDC), depending on many factors including engine speed and load. This ignition advance allows time for the combustion process to develop peak pressure at the ideal time for maximum recovery of work from the expanding gases.[2]
The spark across the spark plug's electrodes forms a small kernel of flame approximately the size of the spark plug gap. As it grows in size, its heat output increases, which allows it to grow at an accelerating rate, expanding rapidly through the combustion chamber. This growth is due to the travel of the flame front through the combustible fuel air mix itself, and due to turbulence which rapidly stretches the burning zone into a complex of fingers of burning gas that have a much greater surface area than a simple spherical ball of flame would have. In normal combustion, this flame front moves throughout the fuel/air mixture at a rate characteristic for the particular mixture. Pressure rises smoothly to a peak, as nearly all the available fuel is consumed, then pressure falls as the piston descends. Maximum cylinder pressure is achieved a few crankshaft degrees after the piston passes TDC, so that the force applied on the piston (from the increasing pressure applied to the top surface of the piston) can give its hardest push precisely when the piston's speed and mechanical advantage on the crank shaft gives the best recovery of force from the expanding gases, thus maximizing torque transferred to the crankshaft.[2][3]
Abnormal combustion[edit]
Main article: Cool flame
When unburned fuel/air mixture beyond the boundary of the flame front is subjected to a combination of heat and pressure for a certain duration (beyond the delay period of the fuel used), detonation may occur. Detonation is characterized by an almost instantaneous, explosive ignition of at least one pocket of fuel/air mixture outside of the flame front. A local shockwave is created around each pocket and the cylinder pressure will rise sharply, and possibly beyond its design limits causing damage.
If detonation is allowed to persist under extreme conditions or over many engine cycles, engine parts can be damaged or destroyed. The simplest deleterious effects are typically particle wear caused by moderate knocking, which may further ensue through the engine's oil system and cause wear on other parts before being trapped by the oil filter. Such wear gives the appearance of erosion, abrasion, or a "sandblasted" look, similar to the damage caused by hydraulic cavitation. Severe knocking can lead to catastrophic failure in the form of physical holes melted and pushed through the piston or cylinder head (i.e., rupture of the combustion chamber), either of which depressurizes the affected cylinder and introduces large metal fragments, fuel, and combustion products into the oil system. Hypereutectic pistons are known to break easily from such shock waves.[3]
Detonation can be prevented by any or all of the following techniques:
the use of a fuel with high octane rating, which increases the combustion temperature of the fuel and reduces the proclivity to detonate
enriching the air–fuel ratio which alters the chemical reactions during combustion, reduces the combustion temperature and increases the margin above detonation
reducing peak cylinder pressure
decreasing the manifold pressure by reducing the throttle opening or boost pressure
reducing the load on the engine
retarding (reduce) ignition timing
Because pressure and temperature are strongly linked, knock can also be attenuated by controlling peak combustion chamber temperatures by compression ratio reduction, exhaust gas recirculation, appropriate calibration of the engine's ignition timing schedule, and careful design of the engine's combustion chambers and cooling system as well as controlling the initial air intake temperature.
The addition of certain materials such as lead and thallium will suppress detonation extremely well when certain fuels are used.[citation needed] The addition of tetraethyllead (TEL), a soluble organolead compound added to gasoline was common until it was discontinued for reasons of toxic pollution. Lead dust added to the intake charge will also reduce knock with various hydrocarbon fuels. Manganese compounds are also used to reduce knock with petrol fuel.
Knock is less common in cold climates. As an aftermarket solution, a water injection system can be employed to reduce combustion chamber peak temperatures and thus suppress detonation. Steam (water vapour) will suppress knock even though no added cooling is supplied.
Certain chemical changes must first occur for knock to happen, hence fuels with certain structures tend to knock easier than others. Branched chain paraffins tend to resist knock while straight chain paraffins knock easily. It has been theorized[citation needed] that lead, steam, and the like interfere with some of the various oxidative changes that occur during combustion and hence the reduction in knock.
Turbulence, as stated, has very important effect on knock. Engines with good turbulence tend to knock less than engines with poor turbulence. Turbulence occurs not only while the engine is inhaling but also when the mixture is compressed and burned. Many pistons are designed to use "squish" turbulence to violently mix the air and fuel together as they are ignited and burned, which reduces knock greatly by speeding up burning and cooling the unburnt mixture. One example of this is all modern side valve or flathead engines. A considerable portion of the head space is made to come in close proximity of the piston crown, making for much turbulence near TDC. In the early days of side valve heads this was not done and a much lower compression ratio had to be used for any given fuel. Also such engines were sensitive to ignition advance and had less power.[3]
Knocking is more or less unavoidable in diesel engines, where fuel is injected into highly compressed air towards the end of the compression stroke. There is a short lag between the fuel being injected and combustion starting. By this time there is already a quantity of fuel in the combustion chamber which will ignite first in areas of greater oxygen density prior to the combustion of the complete charge. This sudden increase in pressure and temperature causes the distinctive diesel 'knock' or 'clatter', some of which must be allowed for in the engine design.
Careful design of the injector pump, fuel injector, combustion chamber, piston crown and cylinder head can reduce knocking greatly, and modern engines using electronic common rail injection have very low levels of knock. Engines using indirect injection generally have lower levels of knock than direct injection engine, due to the greater dispersal of oxygen in the combustion chamber and lower injection pressures providing a more complete mixing of fuel and air. Diesels actually do not suffer exactly the same "knock" as gasoline engines since the cause is known to be only the very fast rate of pressure rise, not unstable combustion. Diesel fuels are actually very prone to knock in gasoline engines but in the diesel engine there is no time for knock to occur because the fuel is only oxidized during the expansion cycle. In the gasoline engine the fuel is slowly oxidizing all the time while it is being compressed before the spark. This allows for changes to occur in the structure/makeup of the molecules before the very critical period of high temp/pressure.[3]
Knock detection[edit]
Due to the large variation in fuel quality, a large number of engines now contain mechanisms to detect knocking and adjust timing or boost pressure accordingly in order to offer improved performance on high octane fuels while reducing the risk of engine damage caused by knock while running on low octane fuels.
An early example of this is in turbo charged Saab H engines, where a system called Automatic Performance Control was used to reduce boost pressure if it caused the engine to knock.[4]
Various monitoring devices are commonly utilized by tuners as a method of seeing and listening to the engine in order to ascertain if a tuned vehicle is safe under load or used to re-tune a vehicle safely.
Knock prediction[edit]
Since the avoidance of knocking combustion is so important to development engineers, a variety of simulation technologies have been developed which can identify engine design or operating conditions in which knock might be expected to occur. This then enables engineers to design ways to mitigate knocking combustion whilst maintaining a high thermal efficiency.
Since the onset of knock is sensitive to the in-cylinder pressure, temperature and autoignition chemistry associated with the local mixture compositions within the combustion chamber, simulations which account for all of these aspects[5] have thus proven most effective in determining knock operating limits and enabling engineers to determine the most appropriate operating strategy.
Knock Control[edit]
The objective of knock control strategies is to attempt to optimize the trade-off between protecting the engine from damaging knock events and maximizing the engine’s output torque. Knock events are an independent random process.[6] It is impossible to design knock controllers in a deterministic platform. A single time history simulation or experiment of knock control methods are not able to provide a repeatable measurement of controller’s performance because of the random nature of arriving knock events. Therefore, the desired trade-off must be done in a stochastic framework which could provide a suitable environment for designing and evaluating different knock control strategies performances with rigorous statistical properties.
References[edit]
Jump up ^ "Archived copy". Archived from the original on 18 March 2016. Retrieved 16 March 2016.
^ Jump up to: a b Jack Erjavec (2005). Automotive technology: a systems approach. Cengage Learning. p. 630. ISBN 1-4018-4831-1.
^ Jump up to: a b c d H.N. Gupta (2006). Fundamentals of Internal Combustion Engines. PHI Learning. pp. 169–173. ISBN 81-203-2854-X.
Jump up ^ "Turbocharger with a brain". Popular Science. Bonnier. 221 (1): 85. July 1982.
Jump up ^ "Advanced simulation technologies". cmcl innovations, UK. Archived from the original on 9 April 2011. Retrieved 12 June 2010.
Jump up ^ Jones, J. C. Peyton; Frey, J.; Shayestehmanesh, S. (July 2017). "Stochastic Simulation and Performance Analysis of Classical Knock Control Algorithms". IEEE Transactions on Control Systems Technology. 25 (4): 1307–1317. doi:10.1109/TCST.2016.2603065. ISSN 1063-6536. Archived from the original on 1 May 2018.
Further reading[edit]
Identification of combustion and detonation in spark ignition engines using ion current signal Fuel 227, 469-477 (2018), DOI:10.1016/j.fuel.2018.04.080
Modeling of in-cylinder pressure oscillations under knocking conditions: A general approach based on the damped wave equation, FUEL Journal, DOI:10.1016/j.fuel.2012.07.066, ISSN 0016-2361, Feb., 2013.
Experimental Evaluation of Reduced Kinetic Models for the Simulation of Knock in SI Engines, SAE Technical Paper n. 2011-24-0033, DOI: 10.4271/2011-24-0033, ISSN 0148-7191, Sep., 2011.
Modeling Pressure Oscillations Under Knocking Conditions: A Partial Differential Wave Equation Approach, SAE Technical Paper n. 2010-01-2185, DOI 10.4271/2010-01-2185, ISSN 0148-7191, Oct., 2010.
Predictive combustion simulations for “downsized” direct injection spark-ignition engines: solutions for pre-ignition (“mega-knock”), misfire, extinction, flame propagation and conventional “knock”, cmcl innovations, accessed June 2010.
Engine Basics: Detonation and Pre-Ignition, Allen W. Cline, accessed June 2007.
Experimental Investigation on the Use of Ion Current on SI Engines for Knock Detection, SAE Technical Paper n. 2009-01-2745, DOI 10.4271/2009-01-2745, ISSN 0148-7191, Nov., 2009.
Charles Fayette Taylor, Internal Combustion Engine In Theory And Practice, Second Edition, Revised, Volume 2, MIT Press, 1985, Chapter 2 on "Detonation and Preignition", pp 34–85, ISBN 9780262700276.
External links[edit]
Pre-ignition and Detonation by Bob Hewitt (Misterfixit) Accessed June 2007
NACA - Combustion and knock in a spark-ignition engine
NACA - Ionization in the knock zone of an internal combustion engine
NACA - Interdependence of various types of autoignition and knock
Avweb - Detonation myths
Misterfixit - What is detonation?
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