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Title: On the mechanism of controlled auto ignition
Authors: Law, Don
Allen, Jeff
Chen, Rui
Keywords: Autoignition
Control systems
Combustion processes
Diesel engines
Fuel economy
Gasoline
Issue Date: 2002
Publisher: © SAE International
Citation: LAW, D., ALLEN, J. and CHEN, R., 2002. On the mechanism of controlled auto ignition. IN: Proceedings from SAE 2002 World Congress, Detroit, USA, 4th-7th March.
Series/Report no.: SAE Technical Papers;2002-01-0421
Abstract: Controlled auto ignition (CAI) is a form of combustion which uses an auto-ignited homogeneous air/fuel mixture but is controlled (or moderated) by regulating the quantity of internal exhaust gas residuals. In this paper, using a fully variable valve train and a newly developed exhaust valve control strategy, we substituted EGR with hot nitrogen or hot air. We found that the internal exhaust gas residuals have both thermal and chemical effects on CAI combustion. To investigate the thermal effect, nitrogen was used as it is a chemically inert gas. Although its temperature was raised to that of the internal exhaust gas residuals during testing, CAI combustion could not be promoted without assistance from a spark in a form of hybrid CAI, thus indicating that exhaust gas residuals have a chemical effect as well. Conversely, with the introduction of oxygen (which in air is a reactant of combustion), no auto ignition combustion occurred until its temperature was increased to 120 degrees C, proving that a minimum thermal condition of an added gas is required to generate auto-ignition. Comparing this EGR introduction, we found that nitrogen has the ability to delay combustion and smooth the pressure increase rate, while oxygen accelerates combustion and turns CAI combustion into an uncontrollable form normally associated with knock. These effects help to explain the contribution of the chemical effect of the EGR on CAI combustion since exhaust gas residuals contain nitrogen as well as chemically active species.
Description: This is a conference paper [2002 © SAE International]. It was posted on this site with permission from SAE International. Further use and distribution of this paper requires permission from SAE International.
Version: Published
URI: https://dspace.lboro.ac.uk/2134/8402
Publisher Link: http://www.sae.org/congress/2002/
ISSN: 0148-7191
Appears in Collections:Conference Papers and Contributions (Aeronautical and Automotive Engineering)

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