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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.

Natural gas is a promising alternative fuel for internal combustion engines because of its clean combustion characteristics and abundant reserves. However, it has several disadvantages due to its low energy density and low thermal efficiency at low loads. Thus, to assist efforts to improve the thermal efficiency of spark-ignited (SI) engines operating on natural gas and to minimize test procedures, a numerical simulation model was developed to predict and optimize the performance of a turbocharged test engine, considering flame propagation, occurrence of knock and ignition timing. The numerical results correlate well with empirical data, and show that increasing compression ratios and retarding the intake valve closing (IVC) timing relative to selected baseline conditions could effectively improve thermal efficiency. In addition, employing moderate EGR ratios is also effective for avoiding knock.