Effects of mixing and chemical parameters on thermal efficiency in a partly premixed combustion diesel engine with near-zero emissions

CATEGORY: ADVANCED ENGINES
International Journal of Engine Research June 2012 vol. 13 no. 3 188-198
Effects of mixing and chemical parameters on thermal efficiency in a partly premixed combustion diesel engine with near-zero emissions
Wanhua Su, Wenbin Yu
whsu@tju.edu.cn
State Key Laboratory of Engines, Tianjin University, China
Abstract
A hybrid combustion control strategy in a partly premixed combustion diesel engine have been developed and carefully optimized for high thermal efficiency and near-zero emissions in a wide engine operation range, up to a gross indicated mean effective pressure of 1.1 MPa. The mixing and chemical control parameters of combustion include fuel injection timing, injection rate pattern (such as multi-pulse injections), boost pressure, exhaust gas recirculation and in-cylinder temperature, regulated by the timing of intake valve closing. The interaction of the control parameters plays a decisive role in the determination of thermal efficiency and exhaust emissions, which are investigated by means of a comparison analysis with sweeping control parameters and data statistics. It is also found that thermal efficiency is more sensitive to combustion control parameters than emissions in clean partly premixed combustion.
Introduction
The effects of mixing rate enhancing parameters and chemical reaction inhibiting parameters on thermal efficiency have not been systematically investigated. Dec et al.10 reported an isolating study on the effect of EGR on HCCI HRRs and NOx emissions. It concluded that ‘even with a constant CA50, EGR reduces the thermal efficiency of the engine up to 2%, resulting in fuel consumption 5–6%. This is caused mainly by the low ratio of specific heat capacity g (Cp/ Cr) of the EGR gas’. Some high-efficiency combustion in diesel engines by burning gasoline using gasoline port injection or direct injection of a blend of gasoline and diesel has been reported; this provided useful enlightenment of high-efficiency and clean combustion technology of PPC by coordinating mixing and fuel chemical properties.7–9 In this study, the comprehensive effects of mixing and chemical control parameters on thermal efficiency and emissions are investigated in a PPC direct-injection diesel engine by using energy balance analysis.
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