Effects of injection pressure and impingement distance on flat-wall impinging spray flame and its heat flux under diesel engine-like condition

Abstract

Heat loss is one of the main causes of energy losses in modern direct injection diesel engines. This heat loss of the engine occurs during combustion, mainly due to the heat transfer between the impinging spray flame and the piston cavity wall. It is of more critical in small size engines. In order to decrease heat transfer, we need to examine the phenomenon of heat transfer through the combustion chamber walls more fully. To achieve this, we investigated the effects of flame impingement on transient heat flux to the wall. By using a constant volume vessel with a fixed impingement wall, the surface heat flux of the wall at the locations of spray flame impingement was measured with three thin film thermocouple heat flux sensors. The combined effect of impingement distance and injection pressure on the heat transfer was investigated parametrically. The results showed that an increase of injection pressure with longer impinging distance led to an increase in the heat transfer coefficient, which had a dominant effect on local heat flux compared with local temperature distribution. Moreover, we confirmed that the relation between Nusselt number and Reynolds number is a useful measure for describing the heat transfer phenomena in diesel combustion.

Effect of Injection Pressure on Local Temperature and Soot Emission Distribution of Flat-Wall Impinging Diesel Flame under Diesel Engine like-Condition

“…Figure 2 shows the impinging flame at three types of injection pressure. Regarding injection rate graphs in previous work [10], luminous flames occur just before the end of injection. Furthermore, comparing three different injection pressure, the luminous flame appears earlier with higher injection pressure.…”

“…The soot concentration is defined from Hotel and Broughton's model which is represent the KL factor. More explanations about KL Factor have already been mentioned in the previous work [9][10].…”

“…Figure 3(a-c) describes the KL factor distribution at injection pressure variations. Based on liquid length data in evaporating conditions, the soot formation region was formed [10]. This liquid length existed before impingement during the injection period.…”

“…In order to elucidate the mechanism of the wall heat transfer during the diesel spray flame impingement, a series of parametric study of wall impinging diesel spray flame combining transient wall heat flux measurements and high-speed optical diagnostics was conducted detailed by authors [9][10][11]. The results indicate how various experimental conditions affect the spray/flame impingement behavior, with considerable heat loss resulting in some cases.…”

Modelling liquid film in modern GDI engines and the impact on particulate matter emissions – Part 1

“…12 The result is that the process of mixing is imperfect/ insufficient and the air-fuel mixture at the time of ignition is not well prepared. 13 In a given engine, Start Of Injection (SOI) and injection pressure/Fuel Rail Pressure (FRP) are two key calibration variables responsible for the quality of the gas-phase mixing process; 14 moreover, they exert a significant influence on the spray-to-wall impact regime and the resulting piston/wall wetting. 15,16 Modern control approaches also incorporate the ability to split the injection process into two or more pulses as a solution to minimise the sprayto-wall impingement reducing the formation of liquid film.…”