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Start Over Publication Type Conference Materials Publication Type Electronic Resources Publisher sae international
113,025 results

12. Triple injection strategies for gasoline compression ignition (GCI) combustion in a single-cylinder, small-bore common-rail diesel engine

Abstract

Implementing triple injection strategies in partially premixed charge-based gasoline compression ignition (GCI) engines has shown to achieve improved engine efficiency and reduced NOx and smoke emissions in many previous studies. While the impact of the triple injections on engine performance and engine-out emissions are well known, their role in controlling the mixture homogeneity and charge premixedness is currently poorly understood. The present study shows correspondence between the triple injection strategies and mixture homogeneity/premixedness through the experimental tests of second/third injection proportion and their timing variations with an aim to explain the observed GCI engine performance and emission trends. The experiments were conducted in a single cylinder, small-bore common-rail diesel engine fuelled with a commercial gasoline fuel of 95 research octane number (RON). While the first injection proportion and timing were fixed at 40% and 170 °CA bTDC, the second injection proportion was varied from 5~20% (i.e. third injection of 40~55%) and the timing was varied from 20 to 80 °CA bTDC. The third injection timing was also swept from 2 to 11 °CA bTDC. The results show that increased second injection proportion causes higher peak in-cylinder pressure and apparent heat release rate (aHRR) due to increased charge premixing. This leads to lower smoke emissions but increased combustion-induced noise and NOx emissions. Despite higher peak in-cylinder pressure, the engine efficiency shows a decreasing trend with increased second-injection proportion because of the increased wall-wetting and lower late-cycle pressure. Advanced second injection timing leads to lower peak in-cylinder pressure and aHRR and thereby decreasing engine efficiency, which is associated with the increased mixture homogeneity. Consequently, the smoke/NOx and combustion-induced noise emissions are reduced while the uHC emissions become higher, similar to homogeneous charge compression ig

Published
2019

13. Influence of Engine Speed on Gasoline Compression Ignition (GCI) Combustion in a Single-Cylinder Light-Duty Diesel Engine

Abstract

The present study aims to evaluate the effects of engine speed ongasoline compression ignition (GCI) combustion implementingdouble injection strategies. The double injection comprises ofnear-BDC first injection for the formation of a premixed charge andnear-TDC second injection for the combustion phasing control. Theengine performance and emissions testing of GCI combustion hasbeen conducted in a single-cylinder light-duty diesel engine equippedwith a common-rail injection system and fuelled with a conventionalgasoline with 91 RON. The double injection strategy was investigatedfor various engine speeds ranging 1200~2000 rpm and the secondinjection timings between 12°CA bTDC and 3°CA aTDC. From thetests, GCI combustion shows high sensitivity to the second injectiontiming and combustion phasing variations such that the advancedsecond injection causes advanced combustion phasing and extendedpre-combustion mixing time, and thereby increasing engineefficiency and decreasing ISFC. This leads to the reduced smoke/uHC/CO emissions but increased combustion noise and NOxemissions, similar to the trends in conventional diesel combustion. Itis found that the increased engine speed requires a higher fuel massper injection to maintain similar IMEP values, leading to lowerefficiency, higher ISFC, and increased combustion noise. The heatrelease rate increases with increasing engine speed but thecombustion phasing is largely unchanged. A typical smoke-NOxtrade-off is found with increased smoke and decreased NOx emissionsat higher engine speed, primarily due to reduced charge premixingtime, which suggests the partially premixed charge-based GCIcombustion behaves similar to conventional diesel combustion withoverall lower smoke and NOx emissions.

Published
2017