Fuel injection concept for the future clean diesel engines
Recent progress of fuel injection system like a common rail system makes higher fuel injection pressure possible. With such a state-of-theart higher injection pressure technology, diesel engine has been improved in all aspects of performance such as higher power density, lower fuel consumption, cleaner exhaust emissions, etc. Injection pressure of latest FIE systems for the heavy duty or passenger car reach around 3000 bar, but the most of such high injection pressure FIE systems are still under development. Their spray characteristics are investigated by using constant volume vessel, although conditions are different from todays engines pressure and temperature. Soot and NOx emission from the engine equipped with such a higher injection pressure FIE is still under investigation. Also, the optimal nozzle dimensions (i.e. number of holes and hole diameter) in accordance with higher injection pressure is still under investigation. In order to estimate emission performances, CFD coupled with many kinds of sub-models about spray combustion is applied as one of the available method. However, a lot of constants in the simulation code have to be calibrated by use of spray measurement data. On the other hand, in this study, soot and NOx emission data from higher injection pressure is estimated by using engine equipped with practical fuel injection system. And optimized number of holes and hole-diameter for higher injection pressure is estimated. Increase in injection pressure causes the increase in spray penetration and the promotion of atomization. As for the atomization, higher the injection pressure, less the improvement in atomization. Thus, in this study, spray penetration is focused on as a main parameter. According to the many empirical models of spray penetration, penetration is mainly determined by the difference between pressure of fuel injection and that of ambient gas. Emissions from higher injection pressure under the same excess air ratio is assumed to be obtained by decreasing in-cylinder gas pressure instead of increasing injection pressure for obtaining certain pressure difference that can keep same spray penetration. As for the calculation of spray penetration, this study applied Dents formula (1971). However, under the constant excess air ratio condition, decreasing in-cylinder gas pressure automatically yields to shorter injection duration. In this study, ’converted injection pressure’ (as is shown in figure) is proposed to estimate how high injection pressure is required without decreasing in-cylinder gas pressure. Converted injection pressure is calculated by Dent’s formula whose input is spray penetration experimentally linked with engine out emission. In order to verify the concept of converted injection pressure, two different engines are applied in this study. At first, a natural aspirated engine with maximum 1600 bar common rail injection system is applied for building soot and NOx estimation models. In this engine test, wide range of emission data is obtained under the various conditions of excess air ratio and pressure difference between injection and in-cylinder gas. The result shows good relationship between converted injection pressure and measured soot. Using this relationship, soot estimation model is built and proposed. In terms of NOx, it has a good relationship with injection duration. Then, in this study NOx estimation model is also built based on injection duration. Next, a turbo charged engine with maximum 2000 bar injection common rail system is applied for evaluating this soot and NOx estimation model. It is found that relative changes of measured emissions follow estimated results. But there is a gap in their absolute value because of different combustion chamber shape and direction of nozzle hole axis. Thus, it is found that proposed soot and NOx estimation model is only effective for their relative change against increase in injection pressure. At last, a trend of the optimal nozzle dimensions accompanied with increase in injection pressure is calculated by using soot and NOx estimation models. The result shows that higher injection pressure requires larger number of nozzle holes and smaller nozzle hole diameter.
Ryouta Minamino Takao Kawabe Hiroshi Omote Shusuke Okada
YANMAR CO.,LTD,Japan
国际会议
上海
英文
1-9
2013-05-13（万方平台首次上网日期，不代表论文的发表时间）