Low temperature premixed combustion within a small bore high speed direct injection (HSDI) optically accessible diesel engine using a retarded single injection

Abstract

An optically accessible single-cylinder high speed direct-injection (HSDI) Diesel engine equipped with a Bosch common rail injection system was used to study low temperature Modulated Kinetics (MK) combustion with a retarded single main injection. High-speed liquid fuel Mie-scattering was employed to investigate the liquid distribution and evolution. By carefully setting up the optics, three-dimensional images of fuel spray were obtained from both the bottom of the piston and the side window. The NOx emissions were measured in the exhaust pipe. The influence of injection pressure and injection timing on liquid fuel evolution and combustion characteristics was studied under similar fuel quantities. Interesting spray development was seen from the side window images. Liquid impingement was found for all of the cases due to the small diameter of the piston bowl. The liquid fuel tip hits the bowl wall obliquely and spreads as a wall jet in the radial direction of the spray. Due to the bowl geometry, the fuel film moves back into the central part of the bowl, which enhances the airfuel mixing process and prepares a more homogeneous air-fuel mixture. Stronger impingement was seen for high injection pressures. Injection timing had little effect on fuel impingement. No liquid fuel was seen before ignition, indicating premixed combustion for all the cases. High-speed combustion video was taken using the same frame rate. Ignition was seen to occur on or near the bowl wall in the vicinity of the spray tip, with the ignition delay being noticeably longer for lower injection pressure and later injection timing. The majority of the flame was confined to the bowl region throughout the combustion event. A more homogeneous and weaker flame was observed for higher injection pressures and later injection timing. The combustion structure also proves the mixing enhancement effect of the liquid fuel impingement. The results show that ultralow sooting combustion is feasible in an HSDI diesel engine with a higher injection pressure, a higher EGR rate, or later injection timing, with little penalty on power output. It was also found that injection timing has more influence on HCCI-like combustion using a single main injection than the other two factors studied. Compared with the base cases, simultaneous reductions of soot and NOx were obtained by increasing EGR rate and retarding injection timing. By increasing injection pressure, NOx emissions were increased due to leaner and faster combustion with better air-fuel mixing. However, smoke emissions were significantly reduced with increased injection pressure.

Optimization of EGR and split injection strategy for light vehicle diesel low temperature combustion

“…Recently, low temperature combustion (LTC) regime has received a lot of interest (Azimov et al, 2009;Henein et al, 2008;Kimura et al, 2001;Brijesh and Sreedhara, 2013;Fang et al, 2008), its basic concept was to reduce the oxygen concentration and combustion temperature which was below the formation temperatures of both NOx and soot, so as to realize simultaneously reduction of NOx and soot emissions (Alriksson and Denbratt, 2006;Potter and Durrett, 2006).…”

Numerical simulation of the fuel trapped in the crevice during a pilot injection in a homogeneous charge compression ignition engine

“…13 However, in HCCI engines, the pilot injection decreases the NO x emissions, while the UHC emissions rise owing to the increase in the amount of fuel trapped in the crevice which does not take part in the oxidation process and flows back to the combustion chamber. Despite extensive research to reduce the emissions from HCCI engines, [14][15][16][17][18][19][20] the emissions of UHCs is still a major challenge. In this work a three-dimensional (3D) numerical model is presented to investigate the accumulation of fuel in the piston-liner crevice during the preinjection process in HCCI engines under lean preinjection conditions and a high compression ratio.…”

Effect of the injection angle on liquid spray development in a high-speed direct-injection optical diesel engine

“…The Mie-scattering technique is a commonly used and powerful method for liquid-phase visualization [20][21][22][23][24][25][26]. This technique with a threedimensional set-up has been successfully applied in an optical diesel engine for spray visualization [27,28]. The objective of the current paper is to use an improved spray visualization technique to investigate the spray-wall interaction in an optical diesel engine.…”