Based on the linear engine prototype designed by the studying team, the combustion characteristic of the linear engine in certain revolution is investigated experimentally. The effect of ignition timing and excess air ratio on combustion characteristic of the linear engine is studied based on cycle-by-cycle control technique. The result shows that the ignition timing has effect on the combustion characteristic of linear engines in certain revolution. Advancing the ignition timing from 1.0mm BTDC (before the top dead center) to 3.0mm BTDC, the peak cylinder pressure increases, the interval between peak cylinder pressure timing and the top dead center reduces, the IMEP (indicated mean effective pressure) is down, the instantaneous heat release rises and the total heat release decreases. The excess air ratio has apparently effect on combustion characteristic of linear engines in certain revolution. Reducing the excess air ratio from 1.45 to 1.35, the peak cylinder pressure increases, the peak cylinder pressure timing is closer to the top dead center, the instantaneous heat release and the total heat release are larger.

A unique linear engine system is designed independently using eccentric-slider starting system which has been simulated and optimized. Based on the linear engine prototype, the no-load experiment and normal starting experiment are conducted in order to validate the practicality of the eccentric-slider starting system and research the starting characteristics of the linear engine system. The results show that the linear engine can operate smoothly with the starting system under the control logic based on piston displacement and engine frequency. Meanwhile the top cylinder pressure is 1.0MPa in compression process and the engine speed increase continuously with the peak combustion cylinder pressure above 2.0MPa in the normal starting experiment.

A starting experiment has been conducted to investigate the effect of ignition timing on the starting characteristics for linear engine designed by the research group independently. The fuel injection pulse and ignition timing are controlled by the electronic control unit (ECU) which is developed based on the piston displacement. The combustion characteristics of the engine in starting process are studied based on the cylinder pressure measured by the transient pressure sensor. The result shows that the best ignition timing for linear engine starting is 2.4mm~2.8mm when the fuel injection pulse is 5.4ms and this best region of ignition timing is also meet the requirement of the combustion in the next several cycles.

A simulation model of the linear engine system is built in this paper. The cylinder pressure data obtained through engine experiments is used to validate the accuracy of the simulation model. Based on the model, the combustion characteristics and external characteristics of the linear engine system were studied. And the maximization model is used to find an optimum operating region of the linear engine. The results show that, as the air fuel ratio(AFR) decreases under a steady engine speed, both the cylinder pressure and brake power increase first and then decrease, reaching their peak value when the AFR is 12. Under this AFR, the maximum brake power is 16.83kW at 6500rpm. Meanwhile, the fuel economy and the power performance reach the optimum combination within 5200rpm and 6500rpm.

According to the operating requirements of the linear range-extender used in range-extended electric vehicle, as well as structures and performances of the self-developed linear engine, a tubular permanent magnet (PM) linear ISG is designed. The impact of varying electromagnetic structure on the performance is studied by finite element analysis (FEA) in electromagnetic field. On that basis, optimum structural parameters for the linear ISG are determined using multi-objective optimization. The results show that the self-designed linear ISG can meet the performance requirements. After optimization, the output power increases 8.7 percent; the no-load induced electromotive force increases 12.1 percent; the standard deviation of detent force shows a 94.6 percent reduction; the efficiency basically remains constant.