Emission regulations are becoming tighter, and Real Driving Emissions (RDE) is proposed as a testing cycle for evaluating modern engine emissions under a wide operation range. For this reason, engine manufacturers have been developing a method to effectively assess engine performances and emissions under a wide range of transient conditions. Transient engine performances can be evaluated efficiently by applying time-series data created by chirp signals. However, when the time-series data produced by the chirp signal are used directly, the engine hardware may damage, and emission performances deteriorate drastically. It is therefore essential to develop a method to avoid these undesirable operating conditions.
This work aims to develop an algorithm to avoid such unrealistic operation conditions for engine performance evaluation. A virtual diesel engine (VDE) model is developed based on a four-cylinder engine using GT-POWER software. The manipulated variables are fuel injection parameters, throttle valve angle, EGR valve angle, and variable nozzle turbocharger (VNT) positions. The engine speed is used as an external input. Excess-air ratio, intake and exhaust pressure and temperature, and maximum pressure rise rate are state variables. Manipulated variables and external inputs are set for each state variable and varied sequentially. Therefore, various unrealistic operating conditions can be determined. The threshold values are changed by observing the state variables and the frequency of manipulated variables using chirp signals. The chirp signal is changed sequentially to avoid unrealistic operations when a state variable exceeds the threshold during the simulation. The results using the developed algorithm show that the unrealistic operating conditions of the diesel engine can be avoided, and the engine operations under transient conditions can be efficiently obtained.