Thermodynamic and experimental researches on matching strategies of the pre-turbine steam injection and the Miller cycle applied on a turbocharged diesel engine

The pre-turbine steam injection and the Miller cycle can be combined together to improve engine performances, but matching strategies of those two approaches under different operating conditions still need to be clarified. In this paper, thermodynamic processes of the pre-turbine steam injection and the Miller cycle are studied first followed by matching strategies based on a non-dimensional matching map. Experiments are also conducted to show merits of this new system applied on a turbocharged diesel engine. The results show that the steam mass flow rate has a much bigger effect on air supplying characteristics of the turbocharger than the steam temperature, while the Miller cycle degree shows a big influence on the air consuming characteristics of the engine. With the steam/exhaust gas mass flow ratio of 0.1, the fuel economy under full load conditions can be improved by up to 5.9% at 1500 rpm. At the rated speed of 2100 rpm, the fuel economy deteriorates by 1.3% with the steam injection but can be improved by 2.8% further combined with the Miller cycle. Thus, different matching strategies of those two approaches should be adopted under different engine conditions.