This paper reports on the global analysis of the EGR circuit in a HSDI diesel engine and its influence on engine transient operation. To achieve this, the employed methodology was a combination of experimental tests and theoretical calculations.
The experimental work was performed in a fully instrumented engine test bench equipped with an electronically controlled brake able to simulate the European driving cycle (ECE test cycle). Beside this, the theoretical calculations consisted of simulating the accelerations performed in the ECE test cycle by means of a 1-D gas dynamic code that has been adjusted according to the experimental results. This code takes into account the transport of different species through the engine ducts and has been updated related to the transient feature in order to accept different drag force configurations, road gradients and vehicle specifications.
In addition, by using the 1-D model, a parametric study was performed in order to study the effects of thermal efficiency of the EGR cooler, the pressure losses at the EGR line and the combination of both, i.e. what happens when the EGR cooler gets dirty. Finally, the benefits of an electrically controlled EGR valve were analyzed showing that a correct design of control parameters can considerably improve the EGR rates achieved during ECE cycle accelerations.