ABSTRACT
Diesel-ethanol (DE) fuel blends, also called diesohols, are known to reduce NOx emissions from Compression Ignition (CI) engines. Engine researchers in the past have investigated the effects of DE fuel blends on the combustion and emissions performance of CI engines. However, conflicting results have been reported about the effect of DE fuel blends on engine-out NOx, and CO emissions. Furthermore, the emission results of previous researchers in this field were largely focused on the levels of the regulated emissions (NOx, CO, Total Hydrocarbons (THC), and Particulate Number (PN)). This has created an information gap in terms of the emission levels of Volatile Organic compounds (VOCs) such as benzene, and aldehydes, which are harmful to human health. The aim of this work was to extensively investigate the effect of DE blend fuels on the performance as well as the combustion behaviour of CI engines. A 5.7 kW engine output or 4.3 kW generator output, single-cylinder diesel Gen-set was used. The investigated fuel blends were 0%, 5%, 10%, and 15% ethanol in diesel while the tested conditions of generator output were idle, 2 kWe (kilowatt electric medium power), and 3 kWe (high power). The speciation of the engine exhaust was carried out by a Fourier Transform Infrared (FTIR) analyser. A dynamic electric mobility particle spectrometer (DMS500) was used to measure the particle size distribution of the exhaust from the engine. It was found that the diesohols increased the Brake Specific Fuel Consumption (BSFC) of the Gen-set, and contrary to what was reported in literature, the DE blends decreased the Brake Thermal Efficiency (BTE) of the engine compared to diesel baseline. The ethanol-blended fuels caused an increase in CO and THC emissions relative to baseline. The maximum reduction in NOx was 37% below the baseline for DE15 at 3 kWe. The investigated DE fuel blends reduced the engine-out particulate emissions compared to the baseline at the high power condition but led to a significant rise in the aldehydes emissions. Ethanol and benzene emissions also increased compared to the baseline, but the levels were only significant at idle. The use of 15% green ethanol (a zero-carbon fuel) in diesel will reduce CO2 emissions from transport in the UK by 9% (equivalent to 5.5 million tonnes reduction in transport CO2 emissions). The results of the current work will enhance the use of DE biofuel blends in sub-saharan African countries for emission reduction and sustainable power generation. Diesel Gen-sets (without emission after-treatment) are widely used in sub-saharan African countries, where there is a good supply of feedstock for the production of ethanol from Sweet sorghum.
Keywords: Diesohol, combustion, emissions, FTIR, speciation.
