Abstract
This paper begins with a brief introduction to the operating principles of a split-cycle engine that utilizes a valved, intermediary volume to connect the two engine cylinders. Results from experimental testing of the engine fueled with pure methane are presented with a particular emphasis on the combustion duration and phasing. Two different methods of analysing the combustion duration – the mass fraction burn (MFB) and normalized pressure ratio (PRN) – are given. Testing was performed at wide open throttle (WOT) for engine speeds ranging from 850–1200 rpm, and air-fuel equivalence ratios from 0.8–1.0. The results indicate that the main combustion duration is very rapid for all conditions tested, despite late combustion phasing. Changes in spark timing were shown to have a considerable impact on IMEP but did not greatly effect the burn duration. Cyclic variability of IMEP was found to be less than 4% for all cases, except when operation was leaner than ø = 0.85, indicating good combustion stability.
Highlights
The use of natural gas (NG) as a transportation fuel is supported by many appealing attributes associated with the fuel's properties and the resulting combustion characteristics
A split-cycle engine has been developed for this purpose and this paper presents the preliminary combustion characteristics of its operation
The results presented in this paper are focused on the combustion characteristics of the split-cycle engine: in particular, an assessment of the burn duration and combustion stability
Summary
The use of natural gas (NG) as a transportation fuel is supported by many appealing attributes associated with the fuel's properties and the resulting combustion characteristics. The fuel is primarily composed of methane, generally > 90% by volume, which provides excellent knock resistance and the ability to employ higher engine compression ratios. In comparative engine trials between gasoline and NG, Evans and Blaszczyk [1] report lower HC and CO emissions for the majority of conditions tested under NG fuelling, and up to 50% less at certain full load conditions. NOx emissions, are generally on par with gasoline fuelled engines, or slightly higher due to the advanced timing required for the slower combustion of NG. Greenhouse gas emissions are inherently lower on account of a relatively low carbon-to-hydrogen ratio. Interested readers can find a comprehensive review of NG engine performance and emissions characteristics in Cho and He [2], as well as Semin [3] and Korakianitis et al [4]
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