Effect of Load on Close-Coupled Post-Injection Efficacy for Soot Reduction in an Optical Heavy-Duty Diesel Research Engine

Abstract

A s s is ta n t P ro fe sso r M e c h a n ic a l and N uclear E n g in e e rin g D epartm ent, C enter fo r C o m b u s tio n , P ow er and P ro p u ls io n , P e n nsylva nia State U nive rsity, 111 R esearch East B u ild in g , U n iv e rs ity Park, PA 1 6 8 0 2 e -m a il: jx o 2 2 @ e n g r.p s u .e d u M a rk M usculusT e ch n ica l S taff E n g in e C o m b u s tio n D epartm ent, C o m b u s tio n Research F a cility, S andia N ational Lab o ra to rie s, P.O. B ox 969 , M S 9 05 3 , L iv e rm o re , C A 94551 e -m a il: m p m u s c u @ s a n d ia .g o vThe use o f close-coupled post injections is an in-cylinder sOot-reduction technique that has much promise for high efficiency heavy-duty diesel engines. Close-coupled post injec tions, short injections o f fuel that occur soon after the end of the main fuel injection, have been known to reduce engine-out soot at a wide range of engine operating conditions, including variations in injection timing, exhaust gas recirculation (EGR) level, load, boost, and speed. While many studies have investigated the performance of post injections, the details of the mechanism by which soot is reduced remains unclear. In this study, we have measured the efficacy of post injections over a range of load conditions, at constant speed, boost, and rail pressure, in a heavy-duty optically-accessible research diesel engine. Here, the base load is varied by changing the main-injection duration. Measurements of engine-out soot indicate that not only does the efficacy of a post injection decrease at higher engine loads, but that the range of post-injection durations over which soot reduction is achievable is limited at higher loads. Optical measurements, including the natural luminescence of soot and planar laser-induced incandescence of soot, provide information about the spatiotemporal development of in-cylinder soot through the cycle in cases with and without post-injections. The optical results indicate that the post injection behaves similarly at different loads, but that its relative efficacy decreases due to the increase in soot resulting from longer main-injection durations.

Analysis of Mixture Formation Process in a Diesel Engine with Post Injection

“…Many studies have been carried out on the reduction in soot emission from diesel engines by close-coupled post injection, in which a small amount of fuel is injected during the combustion of main sprays . Among them, several studies have demonstrated the sootreduction effects of post injection and investigated the soot-reduction mechanisms for heavy-duty diesel engines [15][16][17][18][19][20][21]. For example, O'Connor and Musculus [18] performed experiments using a heavy-duty (HD) optical diesel engine.…”

Numerical Investigation and Multi-Objective Optimization of Internal EGR and Post-Injection Strategies on the Combustion, Emission and Performance of a Single Cylinder, Heavy-Duty Diesel Engine

“…It is defined as dividing the main single injection profile in two or more injection pulses with definite delay dwell between the injections [12]. Post-injection, which refers to the small amount of fuel (typically up to approximately 20% of total fuel) [13] injected for a short time after the main injection, is one of the effective multiple injection strategies used to reduce in-cylinder soot emission [14,15].…”