Engine performance, gaseous emissions & soot agglomerates from a diesel engine fuelled with diesel-biodiesel-ethanol blends

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Engine performance, gaseous emissions & soot agglomerates from a diesel engine fuelled with diesel-biodiesel-ethanol blends

 

Author: Tse, Ho Jeff
Title: Engine performance, gaseous emissions & soot agglomerates from a diesel engine fuelled with diesel-biodiesel-ethanol blends
Degree: Eng.D.
Year: 2015
Subject: Diesel motor.
Biodiesel fuels.
Diesel motor exhaust gas.
Diesel motor -- Alternative fuels.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Mechanical Engineering
Pages: 171 pages : illustrations (some color)
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2826168
URI: http://theses.lib.polyu.edu.hk/handle/200/8248
Abstract: This study investigated the influence on the engine performance, combustion characteristics, regulated gaseous emissions and soot agglomerates of a 4-cylinder naturally-aspirated direct-injection diesel engine fuelled with diesel-biodiesel-ethanol blended (DBE) fuels under different operating conditions and supplemented with intake carbon-dioxide (CO₂) dilution. Four sets of experimental investigations were adopted. Firstly, the engine was tested at steady speed of 1800 rev/min under five engine loads when fuelled with diesel-biodiesel contained 15% by volume of biodiesel while the ethanol volume varied from 0% to 20%, at a step of 5%. Secondly, the correlations between combustion characteristic parameters and the particulate emissions for DBE blends were studied. Thirdly, the combined effect of DBE blends and intake CO{208} dilution of 1.5% to 4.5% (at 1.5% interval) was evaluated and tested under a high engine load. Lastly, the effect of DBE blends on particulate volatility, oxidation properties and nanostructures was investigated.Experimental results indicate that brake specific fuel consumption (BSFC) increases with ethanol in DBE blends and the increase becomes slight due to improved brake thermal efficiency (BTE) at high engine loads. BTE also increases with ethanol, but again, the increase becomes slight when cooling effects of ethanol are nullified with the high in-cylinder gas temperature at high engine loads. From low to medium engine loads,in-cylinder pressure curves of DBE blends shift away from the top dead centre to the right when increasing ethanol contents. But at high loads, there is no significant change in cylinder pressure rise with ethanol addition as a result of shortened ignition delay period and consequently less fuel accumulates and burns in the premixed phase. On emissions, DBE blends can in general reduce NOX, CO, CO₂, particulate mass and number concentrations while HC might increase.
Compared with ultra-low-sulfur diesel (ULSD), DBE blends can effectively reduce brake specific particulate mass (BSPM), brake specific number concentrations (BSPN) and maintain a good trade-off relationship among PM-PN-NOX. Compared with biodiesel, the blended fuels perform better in suppressing BSPN, leading to a reduction in the numbers of ultrafine and nano-particles.With CO₂ intake charge dilution to diesel engine fuelled by DBE blends tested at a high engine load, the results show reduction of NOX while minimizing the adverse impact on particulate emissions. It is found that the combined effect of DBE blends with intake CO₂ dilution has marginal effects on BSFC and BTE, significantly reduced NOx emission while slightly increased particulate emissions. On particulate characteristics, the results show that DBE blends reduce the volatile organic fractions (VOFs) and particulate mass-number concentrations. The reactivity of particulates decreases in the order of biodiesel, DBE20, DBE10, DBE5, DBE0 and ULSD. It is found that with increasing oxygen content in the fuel, the percentage of VOF increases,the soot burnt-out temperature decreases (lower activation energy), the primary particle size decreases, and there are more curved, tortuous and disorganized nanostructures, all of which favor stronger oxidation rate and higher burnt-out rate of particles in the exhaust.

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