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ABSTRACT
In order to enhance combustion phasing control and reduce cyclic variations in flame propagation/auto-ignition hybrid combustion, a concept of dimethyl ether (DME) micro flame ignition (MFI) hybrid combustion is proposed and studied in an optical engine. Three-stage heat release characteristics can be observed in its main combustion period, which are the rapid but short DME auto-ignition in the first stage, followed by slower flame propagation observed from the outer rim of the DME auto-ignition zone, and, at last, the intense heat release of the end-gas auto-ignition. The DME injection timing can be used to effectively control the combustion phasing and the early stage heat release characteristics. Compared to the spark ignition-controlled auto-ignition (SI-CAI) hybrid combustion, the DME MFI hybrid combustion shows great benefits in stabilizing combustion, which is caused by the accelerated flame formation and propagation speed due to larger area of ignition source and higher ignition energy.
Funding
This work was supported by the State Key Project of Fundamental Research Plan (grant number 2013CB228403) from the Ministry of Science and Technology, and by a Project of the National Nature Science Foundation of China (grant number 91441122) from the National Nature Science Foundation Committee of China.
Nomenclature
| ASOI | = | after start of injection |
| ATDC | = | after top dead center |
| BTDC | = | before top dead center |
| CA | = | crank angle |
| CA05 | = | crank angle of 5% burned mass |
| CA90 | = | crank angle of 90% burned mass |
| CAauto | = | crank angle of the end-gas auto-ignition |
| CAinf | = | crank angle of the inflection point |
| CAI | = | controlled auto-ignition |
| CMOS | = | complementary metal oxide semiconductor |
| DI | = | direct injection |
| DME | = | dimethyl ether |
| ECU | = | engine control unit |
| eEGR | = | external exhaust gas recirculation |
| GDI | = | gasoline direct injection |
| HCCI | = | homogeneous charge compression ignition |
| HRR | = | heat release rate |
| HSC | = | high speed camera |
| ICCD | = | intensified charged-couple device |
| IMEP | = | indicated mean effective pressure |
| LPG | = | liquid petroleum gas |
| LRS | = | laser Rayleigh scattering |
| MFI | = | micro flame ignition |
| PDRZ | = | probability density of reaction zone |
| PFI | = | port fuel injection |
| PIV | = | particle image velocimetry |
| PRF | = | primary reference fuel |
| SFI | = | stratified flame ignition |
| SI | = | spark ignition |
| SI-CAI | = | spark ignition-controlled auto-ignition |
| SNR | = | signal-to-noise ratio |
| SOI | = | start of injection |
| TDC | = | top dead center |