Huili Dou

Research and Development of Heavy-Duty NG Engine and its Key Technologies of Combustion

In this paper, A heavy-duty NG engine and its electronic controlled system were developed. combustion stability, in–cylinder flow, burning rate and hazardous emissions were further investigated to develop optimized combustion control technologies for efficient and clean combustion on this engine. The electronic controlled system and NG supply system were designed in the condition of maintaining the universal parts of based diesel engine as many as possible. The combustion and emissions of NG engine were investigated by means of experiment and numerical simulation with the commercial 3D-CFD-tool STAR-CD. The in-cylinder flow and burning rate of NG engine were studied. Special-shaped combustion chamber was used to change the flow state. The results show that the engine thermal efficiency increases by 2 % compared with the original engine while using the cross-type rapid combustion chamber under 1450r/min,100 % load operating condition. Effect of three kinds of dilution methods on combustion and emissions performance from lean burn NG engine was investigated. These dilution methods include air dilution, stoichiometric combustion with EGR, and double dilution (extra air and EGR). The results show that double dilution method is superior to other methods no matter considering from fuel economy or NOx emissions.

Effects of EGR rate and excess air ratio on the combustion characteristics of compressed natural gas engine

The influence of EGR (exhaust gas recirculation) rate and excess air ratio (λ) on the combustion and emissions of a twofold dilution compressed natural gas (CNG) engine CA6SE3-21E4N were investigated experimentally to solve the limited decreasing-ability on NOx emissions with air dilution. The results show that as EGR rate and λ increase, the peak of cylinder pressure and heat release rate decrease and delay, the heat release centroids and the start of combustion move backward, the main combustion duration becomes longer and then the flame propagation velocity slows down. The cyclic variations intensify versus the EGR rate and λ increase. With smaller λ than that of air dilution under equivalent NOx emission levels, the twofold dilution makes the engine operating more stably. Considering the trade-off between NOx emissions and fuel economy, values as optimal control point can be obtained under 1750r/min, 75% load conditions, namely, λ is 1.35, EGR rate is 7%.