Managing controlled auto-ignition combustion by injection on a direct-injection gasoline engine

Abstract

Controlled auto-ignition (CAI) combustion in gasoline engines has great potential for reducing both NO x emissions and fuel consumption, but its application is still hindered by the lack of direct control of combustion phasing and by the limited CAI operation range. In this paper, the effect of injection timing and split injection on CAI combustion is presented in a single-cylinder direct-injection gasoline engine with an air-assisted injector. The CAI combustion was achieved by trapping some of the burned gases within the cylinder by using low-lift short-duration camshafts and early closure of the exhaust valves. During the experiments, the engine speed was varied from 1200 to 2400 r/min and the air-fuel ratio was altered from stoichiometric to the misfire limit. Both single and split injections were investigated at different injection timings and fuel quantities. The experimental results show that injection timing has an important effect on CAI combustion for single and split injections. Early injection produces faster and more stable combustion, less hydrocarbon and CO emissions, but very rapid heat release rates and higher NO x emissions. The CAI operation range could be extended significantly by early injection. Split injection gives even further extension of the CAI range in both stoichiometric and lean mixture operations. These results indicate that optimizing the injection timing and using split injection is an effective way to control and extend CAI operation in a direct-injection gasoline engine.

CAI Combustion with Methanol and Ethanol in an Air-Assisted Direct Injection SI Engine

“…These fuel properties may provide a fundamental effect in mixture formation and therefore demonstrate differences in self-ignition and CAI combustion processes. Fig.12 shows distribution of liquid and vapor phases during gasoline/air mixing in the upper part of the cylinder at the SOI of 120°CA [19]. These LIF (laser induced fluorescence) images were taken on the same engine with original SI operating setup (using original cam in Fig.2) and fuelled with gasoline.…”

“…Injection timing is another important factor to be able to significantly affect CAI combustion of methanol and ethanol. Injection in the exhaust process may exhibit different CAI combustion characteristics with injection in (b) 180°CA (c) 270°CA Fig.12 Distribution of liquid and vapour phases of gasoline fuel in upper part of the cylinder at SOI of 120°CA [19] the intake process because fuels have been greatly vaporized and mixed with air and residuals, or in other words, re-conditioned or reformed, during the recompression process. This investigation in the future also helps to understand CAI combustion differences of methanol and ethanol on port injection SI engines and on direct injection SI engines.…”

Study of the engine configuration effect on the maximum achievable load in CAI using water injection

“…Some of these approaches are well known, like EGR introduction, 12,13 charge stratification, 14 whereas others more specialized for CAI combustion, as for instance: fuel injection adapted strategies, valve train modifications or fuel composition adaptations. [15][16][17][18][19] In this work, the selected approach to overcome these limitations is based on the introduction of reaction suppressors within the charge in order to get a better control of the charge reactivity, thus optimizing the combustion process.…”

“…Some of these approaches are well known, like EGR introduction, 12,13 charge stratification, 14 whereas others more specialized for CAI combustion, as for instance: fuel injection adapted strategies, valve train modifications or fuel composition adaptations. 15–19…”

Potential of water direct injection in a CAI/HCCI gasoline engine to extend the operating range towards higher loads

“…The GCAI (Gasoline-CAI) combustion process is currently under extensive research to overcome these limitations. Several works develop different strategies to achieve CAI operation on 4-stroke engines, such as: intake air heating, higher compression ratios, residual gas trapping and exhaust gas rebreathing [8][9][10][11]. These strategies have been proved most effective in achieving CAI combustion, and the corresponding works have demonstrated their potential to be incorporated in production gasoline engines.…”