An experimental investigation of the combustion process and the injection strategy of a heavy-duty diesel engine equipped with a common rail fuel injection system

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Heavy-duty (HD) diesel vehicles exert significant environmental impact, especially in the case of nitrogen oxides (NOx) and soot, despite representing a relatively small portion of the overall vehicle population. Modern HD diesel engines employ multi-pulse fuel injection strategies to optimize the combustion process to achieve a better compromise between fuel economy and tail-pipe emissions, especially NOx. As such, improving our understanding of the combustion process and the characteristics of modern HD diesel engines operating under various fuel injection strategies is imperative. This research investigates the fuel injection strategy, combustion process and exhaust emissions of a Navistar 2021 MY HD E39 diesel engine. The impact of engine speed, load and injection strategy on engine performance, the combustion process, engine-out NOx and SCR efficiency is experimentally investigated. The relationships between these parameters provide a better understanding of the influence of the injection strategies on the combustion process, fuel economy and exhaust emissions. Fuel was injected into the cylinder with up to four injection pulses, including up to two pilot injections followed by one main injection pulse and one post injection pulse. The heat release process is featured with three peaks. The first and second peaks are associated with the combustion of fuel injected during the pilot and main fuel injection pulses, respectively. However, the third peak observed at medium to high load is associated with the combustion of fuel injected during post injection process. In comparison to its predecessors, the third peak observed at low load was associated with the diffusion combustion of fuel injected during the main injection pulse. The combustion process, which occurred at medium to high loads, was optimized to achieve high engine thermal efficiency, with the peak cylinder pressure held within the allowed limit while the exhaust temperature was high to achieve acceptable SCR efficiency. In comparison, the combustion phasing at low load was dramatically retarded to increase the exhaust temperature with the aim of maintaining SCR efficiency. The strategies for achieving the ideal compromise between fuel economy and tailpipe emissions are discussed and presented herein.