An Experimental and Numerical Investigation on the Effect of Post Injection Strategies on Combustion and Emissions in the Low-Temperature Diesel Combustion Regime

2013

SAE Int. J. Engines

140

This work is a technical review of past research and a synthesis of current understanding of post injections for soot reduction in diesel engines. A post injection, which is a short injection after a longer main injection, is an in-cylinder tool to reduce engine-out soot to meet pollutant emissions standards while maintaining efficiency, and potentially to reduce or eliminate exhaust aftertreatment. A sprawling literature on post injections documents the effects of post injections on engine-out soot with variations in many engine operational parameters. Explanations of how post injections lead to engineout soot reduction vary and are sometimes inconsistent or contradictory, in part because supporting fundamental experimental or modeling data are often not available. In this paper, we review the available data describing the efficacy of post-injections and highlight several candidate in-cylinder mechanisms that may control their efficacy. We first discuss three in-cylinder mechanisms that have been frequently proposed to explain how post injections reduce engine-out soot. Thereafter, to provide a foundation for interpretation of past research, we briefly review basic soot formation and oxidation chemistry, and soot/fluid processes in fuel sprays and engine flows. Next, we provide a comprehensive overview of the literature on the efficacy of post-injections for soot reduction as a function of engine operational parameters including injection duration and dwell, exhaust-gas recirculation, load, boost, speed, swirl, and spray targeting. We conclude by identifying major remaining research questions that need to be addressed to help achieve a design-level understanding of the mechanisms of soot reduction by post injections.

Section: Enhanced Mixingmentioning

confidence: 99%

Post Injections for Soot Reduction in Diesel Engines: A Review of Current Understanding

2013

SAE Int. J. Engines

140

“…The most prevalent explanation is that the post-injection jet enhances mixing of the main-injection mixture with fresh oxygen [13,15,17,20,23,[26][27][28][29], This mixing can have two effects. Additionally, enhanced mixing can reduce soot formation by providing more oxygen to the fuel-rich regions where soot is still being formed, thus reducing the local equiva lence ratio and suppressing the further formation of soot [23,30], Additionally, enhanced mixing can reduce soot formation by providing more oxygen to the fuel-rich regions where soot is still being formed, thus reducing the local equiva lence ratio and suppressing the further formation of soot [23,30],…”

Section: Introductionmentioning

confidence: 99%

“…Previous studies have included load in parametric variations to study post-injection performance [18,19,27,28,30,32,40]. Many of these studies varied load as part of a standard drive cycle, such as the new European drive cycle (NEDC) or the European stationary cycle (ESC) [41,42], In this type of study, operational parameters suchn as load, speed, and boost are typically varied simultane ously in order to simulate various operating conditions representa tive of the drive cycle.…”

Section: Introductionmentioning

confidence: 99%

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

Journal of Engineering for Gas Turbines and Power

2014

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.

“…First, the additional mixing can increase soot oxidation by providing more oxygen to regions where soot from the main injection was formed [13,[15][16][17]26]. Additionally, enhanced mixing can reduce soot formation by providing more oxygen to the fuel-rich regions where soot is still being formed, reducing the local equivalence ratio and suppressing further formation of soot [23,30].…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Volume 1: Large Bore Engines; Advanced Combustion; Emissions Control Systems; Instrumentation, Controls, and Hybrids

2013

The use of close-coupled post injections of fuel is an in-cylinder soot-reduction technique that has much promise for high efficiency, heavy-duty diesel engines. Close-coupled post injections, short injections of 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, 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 natural luminescence of soot and planar laser-induced incandescence of soot, provide information about the spatio-temporal 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.