Abstract
In order to study the effect of negative valve overlap on combustion and emission characteristics of a homogeneous charge compression ignition engine fueled with natural gas and hydrogen, the test and the simulation were conducted using an engine cycle model coupling the chemical kinetic reaction mechanism under different valve timing conditions. Results show that the internal EGR formed by using negative valve overlap could heat the inlet mixtures and improve the spontaneous ignition characteristic of the engine. The residual exhaust gas could slow down the heat release rate, decrease the pressure rise rate and the maximum combustion temperature, and reduce the NOx emission simultaneously. Among the three NVO schemes, the strategy of changing the intake valve opening timing individually can create the least power loss, and the symmetric NVO strategy which changes both the exhaust valve closing timing and the intake valve opening timing simultaneously can achieve the best heating effect of inlet mixtures and the satisfactory decrease of combustion temperature, as well as the largest reduction of NOx emission.
Highlights
Hydrogen fueled with natural gas (HCNG) engine is a widely studied hybrid fuel power machine, which combines the advantages of abundant resources of natural gas and fast combustion rate, wide flammability limit, and short quenching distance of hydrogen [1,2,3]
Based on the contemporary reviews, it is found that previous relevant studies are mostly working on the simplification of mechanism of pure CNG or pure H2 in Homogeneous charge compression ignition (HCCI) engines, the basic engine performance simulation, and the characteristics of HCNG-fueled SI engines [18, 27,28,29], and little progress has been made in concerning the influence of negative valve overlap formed by changing valve timing on HCCI engine fueled by HCNG binary mixed fuel
Because this paper studies the homogeneous compression ignition characteristics of binary mixed fuel under negative valve overlap (NVO) strategies, focusing on the prereaction temperature and component concentration, the original mechanism is simplified and reformed
Summary
Hydrogen fueled with natural gas (HCNG) engine is a widely studied hybrid fuel power machine, which combines the advantages of abundant resources of natural gas and fast combustion rate, wide flammability limit, and short quenching distance of hydrogen [1,2,3]. Based on the contemporary reviews, it is found that previous relevant studies are mostly working on the simplification of mechanism of pure CNG or pure H2 in HCCI engines, the basic engine performance simulation, and the characteristics of HCNG-fueled SI engines [18, 27,28,29], and little progress has been made in concerning the influence of negative valve overlap formed by changing valve timing on HCCI engine fueled by HCNG binary mixed fuel. In this paper, combined with the experimental study of hydrogen fueled with natural gas engine, the numerical simulation of HCCI engine under NVO strategy is carried out on the GT-Power software and the CHEMKIN software, and the influence of changing valve timing on combustion and emission characteristics of engine is explored. The different improvements of NVO on the working process of the engine are summarized, which provide a theoretical basis for improving the performance of natural gas-hydrogen HCCI engine in practical application
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