Search Results

Development of LPG SI and CI engines for heavy duty vehicles has been carried out. In order to measure the performance and emissions of an LPG lean burn SI engine, the piston cavity, swirl ratio, and propane-butane fuel ratio were varied and tested. Compared to the bathtub and dog dish cavities, the nebula type cavity showed the best performance in terms of cyclic variation and combustion duration. High swirl improved combustion by achieving a high thermal efficiency and low NOx emissions. A feasibility study of an LPG DI diesel engine also has been carried out to study the effectiveness of the selected cetane enhancing additives:Di-tertiary-butyl peroxide (DTBP). When more than 5 wt% DTBP was added to the base fuel, stable engine operation over a wide range of engine loads was possible. The thermal efficiency of LPG fueled operation was found to be comparable to diesel fuel operation at DTBP levels over 5 wt%.

The oxidation mechanism of DTBP (Di-tertiary-butyl peroxide) and its role in butane oxidation have been investigated, as it pertains to the development of an LPG DI diesel engine. Ignition delay contours were analyzed to investigate the role of DTBP (ϕ≈0.2 to the total oxygen) in butane oxidation. At higher pressure and lower temperature regions, it was apparent that the addition of DTBP significantly enhances the ignition delay of butane, whereas at lower pressures and higher temperatures, this effect diminishes. Results of this study showed that the role of DTBP to enhance the ignition delay of the base fuel is through rapid heat release, rather than by radicals produced by decomposition during the base fuel ignition delay. Formaldehyde is a principal species involved in reactions for heat release in the higher pressure lower temperature region, comparable to diesel engine operating conditions.

A feasibility study of an LPG DI diesel engine has been carried out to study the effectiveness of two selected cetane enhancing additives: Di-tertiary-butyl peroxide (DTBP) and 2-Ethylhexyl nitrate (EHN). When more than either 5 wt% DTBP or 3.5 wt% 2EHN was added to the base fuel (100 % butane), stable engine operation over a wide range of engine loads was possible (BMEPs of 0.03 to 0.60 MPa). The thermal efficiency of LPG fueled operation was found to be comparable to diesel fuel operation at DTBP levels over 5 wt%. Exhaust emissions measurements showed that NOx and smoke levels can be significantly reduced using the LPG+DTBP fuel blend compared to a light diesel fuel at the same experimental conditions. Correlations were derived for the measured ignition delay, BMEP, and either DTBP concentration or cetane number. When propane was added to a butane base fuel, the ignition delay became longer.