Utilizing boost and double injections for enhanced stratified-charge direct-injection spark-ignition engine operation with gasoline and E30 fuels

Abstract

This study systematically explores the effects of injection strategy and exhaust-gas recirculation on boosted stratifiedcharge operation of a direct-injection spark-ignition engine using gasoline and E30 fuels at absolute intake pressures in the range of 100-160 kPa. Nitrogen dilution is used to lower the intake mole fraction of oxygen to simulate the dilution effects of exhaust-gas recirculation. The engine is operated at 1000 r/min with an gross indicated mean effective pressure range of 380-680 kPa. In summary, significant reductions of engine-out NO x and soot emissions can be achieved for stratified operation while still maintaining stable combustion (~2% gross indicated mean effective pressure variability) and high thermal efficiency (~40%). Adding exhaust-gas recirculation significantly suppresses NO x emissions, not only by reducing flame temperatures but also by slowing down the combustion which effectively retards the combustion phasing. A well-designed closely spaced double-injection strategy is key to combustion stabilization and plays an important role to suppress soot emissions. Intake boost allows reaching higher loads with further reduced soot emissions. High-speed dual-camera flame imaging reveals key features of flame propagation for stratified operation with low NO x emissions at high exhaust-gas recirculation levels. Heat release rate-based conditional analysis of flame images shows that compared to single injection, the use of double injections creates a spark plasma that is more stretched out, correlating with a more stable early combustion. It also demonstrates that double injections produce more symmetric flame propagation with smaller soot-containing regions, indicating more favorable fuel distributions. Stratified operation with gasoline and E30 fuels demonstrates similar engine performance and emission levels for double injections. These observations suggest that E0 (gasoline)-E30 fuel blends can be compatible with highly efficient stratified-charge spark-ignited operation. However, for a 50/50 double-injection strategy, E30 showed elevated smoke emissions for operation without intake boost, indicating that certain operating strategies can be adversely affected by the ethanol content of E30 fuel blends.

Effect of Fuel Injection Strategy on the Carbonaceous Structure Formation and Nanoparticle Emission in a DISI Engine Fuelled with Butanol

“…12 of 19 [47,48]. Nonetheless, the net difference recorded between the two fuels suggests that mixture stratification plays the most significant role.…”

“…This can be explained through two different mechanisms. One is that the organized fluid motion is quickly converted into turbulence around TDC [46]; the other is that the interaction with the six fuel jets can induce other velocity components that can even partially cancel out tumble [47,48]. Nonetheless, the net difference recorded between the two fuels suggests that mixture stratification plays the most significant role.…”

Thermo- and Fluid-Dynamic Processes in Direct Injection Engines: THIESEL 2016 Special Issue

“…Summarizing the contents of this Special Issue, we can classify the papers selected in four main categories: modelling, [5][6][7] injection, 12,13 CI 14,16,23,25 and SI. 17,22,24,29 As mentioned above, modelling of combustion processes has progressed considerably in recent years, thanks to the development of better spray and combustion models and the extensive use of parallel computing. Even so, the difficulty lies in choosing the most representative chemistry, as these calculations are rather timeconsuming.…”

“…With respect to SI engines, Catapano et al 22 show an optimization of natural gas direct injection in a transparent engine, while Zeng et al 17 use double injection strategies to increase the operating range of Direct Injection Spark Ignition (DISI) stratified operation. Kru¨ger et al 24 present a combination of experiments and modelling to study the effect of SI dispersion during lean combustion.…”

“…9,10 Hence, laser induced fluorescence-particle image velocimetry (LIF-PIV), high-speed ultraviolet (UV) chemiluminescence imaging and X-ray radiography techniques have to be adapted to obtain all relevant information. [11][12][13][14] New injection strategies, 14,15 new combustion concepts (reactivity controlled compression ignition (RCCI), premixed charge compression ignition (PCCI), gasoline lean combustion, stratified charge operation and low-temperature combustion) [16][17][18] and alternative fuels such as natural gas and biofuels [19][20][21] are currently being explored on one hand in order to improve mixture formation for both compression ignition (CI) and spark ignition (SI) engines and on the other hand in the context of engine downsizing.…”