Improvement of thermal efficiency of a high-boosted diesel engine with focus on peak cylinder pressure

Abstract

The combination of high boosting and high exhaust gas recirculation (EGR) is a practical and effective strategy to achieve simultaneous reductions of fuel consumption and exhaust emissions in diesel engines. To obtain further improvements of fuel efficiency and emissions, the effects of engine parameters including compression ratio, peak cylinder pressure, and the timing of the start of combustion are investigated using a single-cylinder diesel engine under conditions of high boost pressure of 400 kPa and fuel injection pressure of 200 MPa, focusing particularly on the peak cylinder pressure. The experiments show that when the peak cylinder pressure is raised to 28 MPa by adjusting the timing of the start of combustion at 23°after top dead centre (ATDC) at a compression ratio of 18, the lowest specific fuel consumption rate of 185.6 g/kW h, which corresponds to the brake thermal efficiency of 45.2 per cent, is obtained. When the effective compression ratio is lowered by using a variable valve timing system while maintaining the peak cylinder pressure at 28 MPa, the minimum specific fuel consumption of 181.2 g/kW h, which corresponds to a brake thermal efficiency of 46.3 per cent, is obtained.

The effect of combustion type on exhaust emissions and thermal efficiency at partial load operating condition in heavy duty diesel engines

“…This is based on the estimation that the soot mass concentration of 0.35 FSN corresponds to the specific particulate emission of 0.05 g/kWh, and this emission level can be easily reduced below 0.01 g/kWh, the target, if an ordinary diesel particulate filter is equipped. (Aoyagi et al, 2011) Moreover, the intake air temperature after supercharging was cooled by an air cooler and the mixture of intake air and EGR gas was set to a constant 50°C at the intake manifold. Also, fuel injection timing was adjusted so that the high temperature oxidation reaction after low temperature oxidation reaction starts at TDC.…”

“…In this experiment, a high-pressure loop EGR system was adopted, and the intake manifold pressure and exhaust manifold pressure was made equal throughout the tests so that the external work done by supercharging system could be ignored. (Aoyagi et al, 2011) This approach makes it possible to make a direct measurement of the brake mean effective pressure, which includes the pumping loss. In this study, EGR rate is defined by Eq.…”

Optimization of piston bowl and valve system in compression ignition engine fueled with gasoline/diesel/polyoxymethylene dimethyl ethers for high efficiency

“…Murata et al 28 applied a VVT system in a light-duty diesel engine by means of late intake valve closing (LIVC) and achieved a significant NO X and smoke reduction and high thermal efficiency. A brake thermal efficiency of 46.3% was obtained by Aoyagi et al 29 with VVT and high compression ratio. Tomoda et al 30 utilized VVT technology in New European Driving Cycle (NEDC) and NO X emissions was found to be reduced by 40% and fuel consumption by 4%.…”

Potential of variable diffuser vanes for extending the operating range of compressors and for improving the torque performance of turbocharged engines

“…The soot emissions and the NO x emissions from diesel engines have a trade-off relation. However, in the experiments carried out by Aoyagi et al 2,3 and Wakisaka et al, 4 the extremely high pressure intake facilitated simultaneously a reduction in the NO x emissions and a reduction in the soot emissions from diesel engines. For gasoline engines, the cylinder is cooler because of direct injection, which alleviates the knock tendency; this makes a higher boost pressure and further downsizing possible, and thus this combination of turbocharging and direct injection greatly Turbomachinery Laboratory, State Key Laboratory of Automotive Safety and Energy, Tsinghua University, Beijing, People's Republic of China benefits the efficiency of the gasoline engine.…”