Simultaneous imaging of exhaust gas residuals and temperature during HCCI combustion

Simultaneous planar laser-induced fluorescence (PLIF) imaging of exhaust residuals and temperature has been applied throughout the intake and compression strokes of an IC engine for two different kinetically controlled combustion strategies. The first strategy wits traditional homogeneous-charge compression-ignition (HCCI) combustion where intake air heating and a diesel-like fuel (n-heptane) were used in Conjunction with a homogeneous fuel distribution. The second combustion strategy studied was HCCI with a large negative-valve overlap (NVO) and direct injection or fuel during the NVO period. The evolution of the in-cylinder EGR and temperature distributions was measured, and the extent of EGR and temperature non-uniformity at the latest imaging timing determined. For traditional HCCI combustion the resulting distributions of EGR and temperature in-cylinder just prior to combustion achieved a uniform state with 1 sigma distribution widths of 2.2 mole fraction % for the EGR distribution and 4.9 K for the temperature distribution. Operation with large NVO had significantly wider EGR and temperature distributions just prior to combustion owing to the large level of retained exhaust gases with 1 sigma distribution widths of 6.2 mole fraction % for the EGR distribution and 24.5 K for the temperature distribution. The results illustrate that EGR retention can result in significant stratification in the temperature and EGR distributions, and as such may be capable of altering combustion phasing and duration for kinetically controlled combustion strategies. (c) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.