Methane-gasoline dual fuel engine combustion and emissions control technologies

Wahbi, Ammar (2022). Methane-gasoline dual fuel engine combustion and emissions control technologies. University of Birmingham. Ph.D.

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Abstract

Compressed natural gas (CNG) is currently one of the promising and more established alternative to liquid fossil fuels. The combined utilisation of CNG and gasoline in spark-ignition engines can provide strong synergies between the two fuels leading to lower fuel consumption and exhaust emissions. However, no study to date has investigated the performance of the aftertreatment system designed for dual-fuel engines, with all studies either limited to combustion analysis of the dual-fuel or for dedicated CNG fuelled engines.

As such, the aftertreatment system of a dual-fuel gasoline-CNG engine is investigated in this study by the use of several dedicated CNG catalysts. A dual-fuel injection strategy was implemented where methane gas was port-injected into the intake in stoichiometric conditions at levels corresponding to 20 and 40% energy density replacement of gasoline. High, medium and low loaded Pd/Rh catalysts were used and compared to study the effect of PGM loading on the catalyst light-off activity for methane. Results indicate that increasing the Pd loading led to significantly earlier light-off temperatures achieved at relatively lower temperatures of 340, 350 and 395oC respectively. However, the benefit diminishes above Pd loading >142.5 g ft\(^{-3}\). To complement this work, the performance of two full-scale CNG catalysts with different PGM loadings under various engine lambda conditions and cyclic air/fuel ratio was investigated. In addition, cycles have been developed with the aim to enhance fuel economy while reducing exhaust emissions. Additional research into the usage of the dual-fuel injection system to reduce the higher particulate emissions produced by GDI engines, as well as reducing their gaseous exhaust emissions is included in the study. Various characteristics of the released particles, including their size distributions, reactivity, morphology, and nanostructure, were evaluated. Other benefits of the dual-fuel system are presented in this study in terms of 10% and 54% lower engine output CO\(_2\) and CO emissions respectively and up to 90 to 98% reduction in particle number. However, high NH\(_3\) levels were observed primarily formed from steam-reforming reactions due to the increased level of methane in the exhaust stream.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):