| Homogeneous Charge Compression Ignition (HCCI) is a promising combustion process that offers the potential for simultaneous reductions in NOx and PM emissions while has high thermal efficiency. However, for the diesel-fuel HCCI, there are still some critical problems that need to be solved. The low volatility of diesel fuel together with its tendency of auto-ignition attributed to high fuel cetane number makes it extremely difficult to form a homogeneous mixture, control the auto-ignition process and expand HCCI operation range. A fuel injection technology that can help homogeneous mixture formation without fuel wall impingement is in active demand.In order to achieve the multi-stage fuel injection technique, it's necessary to ensure the high-speed electro-magnet response of solenoid of the common rail (CR) injector. Under the drive voltage of 110V, the solenoid has the fastest open and close electro-magnet response. A high performance and noninsulated power supply unit that converts 24V of the battery to 110V was developed based on the operating principle of chopper boost. In addition, the characteristic of output voltage of the convertor was studied when it was used to drive the CR injector.In this paper, modulated multi-pulse injection technology is firstly presented. Based on the PC computer resources of hardware and software, a multi-pulse injection modulation and control system was developed, which simplifies creation and management of the control signals of pulse width and dwell time and by which up to 10 pulses can be flexibly controlled. On the developed system, typical modulated injection modes such as staggered mode (SM), hump mode (HM), progressive increase mode (PIM) and even mode (EM) were designed and realized based on prejudgment of combustion requirement. At the engine speed of 1400rpm, with the typical injection modes, HCCI combustion got near zero NOx and smoke emissions. However, the injection mode must be carefully designed for higher power output. It was found that there were very critical control parameters including multi-pulse injection number, pulse injected fuel mass, pulse injected fuel ratio and dwell time of pulse injection.The study of the expansion of HCCI operation range was also conducted. Under the different engine speeds, such as 1400,1600 and 1800 rpm, HCCI combustion organized by the modulated injection mode also got very low NOx and smoke emissions. However as the engine speed increases, NOx emissions become gradually worse. Therefore, athigher engine speeds, the fuel-air mixture appeared more serious stratification and the modulated injection mode should be getting reduced later injections. It was also found that the effects of intake pressure and injection timing on engine performance were reduced.
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