Experimental study of an automotive Diesel engine efficiency when running under stoichiometric conditions

If run under stoichiometric air–fuel ratio a Diesel engine could use a simple three way catalyst for NOx after-treatment instead of complex and expensive devices. This concept of Stoichiometric Diesel Combustion (SDC) has been experimentally tested on a modern automotive Diesel engine. Injection strategy (injection pressure, phasing, with or without pilot, multi-injection) and intake strategy (exhaust gas recirculation rate, swirl level) have been studied, for three operating points. It appears that, for the best strategies, brake thermal efficiency drops between 5% and 10% as compared with conventional lean Diesel. For each operating point, this drop is analysed with energy balance charts, and combustion rate of heat release. In particular the evolutions of combustion efficiency and gross indicated thermal efficiency are studied and it appears that there are some trades-offs between these two parameters. The evolution of particulate emissions and exhaust temperature are also described and commented. Finally, these results are used to propose some hardware modifications to improve SDC engine efficiency.

► A Diesel engine can run under Stoichiometric Diesel Combustion (SDC).
► SDC increases BSFC between 5% and 10% as compared to conventional lean Diesel.
► BSFC can be improved with a specific injection strategy and exhaust gas recirculation.
► There is a trade-off between combustion efficiency and thermal efficiency.