Effects of fuel combination and IVO timing on combustion and emissions of a dual-fuel HCCI combustion engine
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RESEARCH ARTICLE
Xin LIANG, Jianyong ZHANG, Zhongzhao LI, Jiabo ZHANG, Zhen HUANG, Dong HAN
Effects of fuel combination and IVO timing on combustion and emissions of a dual-fuel HCCI combustion engine
© Higher Education Press 2020
Abstract This paper experimentally and numerically studied the effects of fuel combination and intake valve opening (IVO) timing on combustion and emissions of an n-heptane and gasoline dual-fuel homogeneous charge compression ignition (HCCI) engine. By changing the gasoline fraction (GF) from 0.1 to 0.5 and the IVO timing from –15°CA ATDC to 35°CA ATDC, the in-cylinder pressure traces, heat release behaviors, and HC and CO emissions were investigated. The results showed that both the increased GF and the retarded IVO timing delay the combustion phasing, lengthen the combustion duration, and decrease the peak heat release rate and the maximum average combustion temperature, whereas the IVO timing has a more obvious influence on combustion than GF. HC and CO emissions are decreased with reduced GF, advanced IVO timing and increased operational load. Keywords homogeneous charge compression ignition, dual-fuel, n-heptane, gasoline, intake valve opening timing
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Introduction
In conventional internal combustion (IC) engines, diesel engines have a high thermal efficiency but high emissions of nitric oxides (NOx) and particulate matter (PM). In comparison, gasoline engines produce low NOx and PM emissions but have a low thermal efficiency [1]. With the requirement of thermal efficiency improvement and emissions reduction for IC engines, various advanced combustion strategies have been studied [2–4]. Homogeneous charge compression ignition (HCCI) combines the advantages of diesel engines and gasoline engines, and Received Jan. 6, 2020; accepted Feb. 29, 2020; online Sept. 30, 2020 Xin LIANG, Jianyong ZHANG, Zhongzhao LI, Jiabo ZHANG, Zhen
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HUANG, Dong HAN ( ) Key Laboratory for Power Machinery and Engineering of the Ministry of Education, Shanghai Jiao Tong University, Shanghai 200240, China E-mail: [email protected]
can simultaneously achieve a high thermal efficiency and low NOx and PM emissions under certain operation conditions [5–7]. However, it is difficult to control the HCCI combustion process due to its kinetics-controlled auto-ignition characteristics. In HCCI combustion, fuel chemical properties are the major factors determining the auto-ignition characteristics [8,9]. To accurately control the fuel auto-ignition in HCCI engines and avoid the abnormal combustion phenomena, an effective method of flexibly adjusting fuels with different auto-ignition tendencies according to the engine conditions, also named as dual-fuel technology is often adopted [10–14]. Using a gasoline/diesel dual-fuel engine, Lu et al. [15] investigated the effects of fuel fraction on the combustion and emissions characteristics. The results indicated that the maximum in-cylinder pressure and maximum heat release rate are decreased and the NOx emissions are increased with elevated gasoline fraction. Huang et
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