Characteristics of Pressure Wave in Common Rail Fuel Injection System of HSDI Diesel Engines

The latest generation of HPCR equipment now provides diesel engines possibility to apply as many as eight separate injection pulses within the engine cycle for reducing emissions and for smoothing combustion. With these complicated injection arrangements, optimizations of operating parameters for various driving conditions is considerable difficult, particularly when integrating fuel injection parameters with other operating parameters such as EGR rate and boost pressure together for evaluating calibration results. Understanding the detailed effects of fuel injection parameters upon combustion characteristics and emission formation is therefore particularly critical. In this paper, the results and discussion of experimental investigations on a HSDI light-duty diesel engine testbed are presented for evaluating and analysing effects of main adjustable parameters of the fuel injection system on all regulated emissions gases and torque performance. Main injection timing, rail pressure, pilot amount and particularly pilot timing have been examined. The results show that optimization of each of those adjustable parameters is beneficial for emission reduction and torque improvement under different operating conditions. By exploring the variation of the interval between the pilot injection and the main injection, it is found that the pressure wave in the common rail has a significant influence on the subsequent injection. This suggests that special attentions must be paid for adjusting pilot timing or any injection interval when multi-injection is used. With analysing the fuel amount oscillation of the subsequent injections to pilot separation, it demonstrates that the frequency of regular oscillations of the actual fuel amount or the injection pulse width with the variation of pilot separation is always same for a specified fuel injection system, regardless of engine speed, fuel amount, injection pulse, injection pressure.