Effect of oxygenated biofuels on dual fuel rcci combustion in an automotive diesel engine

Abstract

The advanced combustion concept developed by Engine Research Centre of University of Wisconsin referred as Reactivity Controlled Compression Ignition (RCCI) mode exhibited better combustion control and lower cyclic variability compared to other advanced combustion modes. The challenges underlying in RCCI mode are load extension, unburnt emissions at lower loads and lower combustion efficiency. Increasing fuel efficiency to cut down carbon dioxide (CO2) and minimising the fossil fuel use are other challenges exists in front. Most of the RCCI studies reported with gasoline/diesel and some research reported with alternate fuels. Since RCCI is a dual fuel combustion concept selection of fuel combinations is especially important to achieve the optimised reactivity gradient and reactivity stratification. Hence, in the present work, an attempt was made to address these challenges with the help of oxygenated renewable alternative fuels (like methanol, biodiesel, dimethyl ether and polyoxymethylene dimethyl ether) by implementing effective injection, fuel reformulation to improve the reactivity of high-Octane fuel and aftertreatment strategies. The selection of these fuels helped in improving global reactivity of the charge inside the cylinder because of the higher cetane number of biodiesels, dimethyl ether and polyoxymethylene dimethyl ether compared to diesel. Methanol has got higher Octane number than gasoline which resists the auto-ignition and thereby helps in increasing the ignition delay. Increased ignition delay assists in creating well premixed air-fuel mixture to cut down the oxides of nitrogen. In addition to this, oxygen content in these fuels, absence of carbon-to-carbon bonds helps in eliminating the soot emissions further in the advanced combustion mode. In the present work, a commercial, automotive light-duty diesel engine was considered for the research work. To perform dual fuel RCCIcombustion, the test engine was modified for admitting two fuels by integrating a multi-point fuel injection system