Suitability of Biofuels and Plastic Oil Blended With Diesel in CRDI Engine

Abstract

Nitrogen oxides and smoke are the substantial emissions for the diesel engines. Fuels comprising high-level oxygen content can have low smoke emission and higher efficiency due to better combustion. The objective of this research is to assess the potential to employ oxygenated fuels such as dimethyl ether, ethanol and butanol, and waste plastic oil in direct injection engine as alternative fuels for diesel. To reduce NOX, exhaust gas recirculation technology for various fuels is studied. Computational fluid dynamics (CFD) studies on combustion and emission characteristics of common rail direct injection (CRDI) engines using oxygenated fuel-diesel blends are less developed and still under intense study. In view of that detailed CFD simulation is carried out in present study and also validated with experimental results. Ethers are favourable alternative for diesel engine due to their chemical structure. Presence of more oxygen, absence of carbon-carbon (C-C) bond in chemical structure, and high cetane number of dimethyl ether (DME), cause less pollution in DME operated engine compared to diesel engine. Study emphasizes the effect of various EGR rates (0-20%) and DME-diesel blends (0-20%) on combustion characteristics and exhaust emissions of CRDI engine using CFD simulation. Results show that, due to better combustion characteristics of DME, indicated thermal efficiency (ITE) increases with the increase in DME- diesel blends. Ethanol is an attractive alternative fuel because it is oxygenated, renewable and bio-based resource; thereby it has potential to reduce smoke emissions in compression-ignition engines. CFD simulation is carried out to study the effect of EGR and injection timing on the performance, combustion and exhaust emission characteristics of CRDI engine fuelled with bioethanol-diesel blends. The results indicate that the mean CO formation and ignition delay increase whereas mean NOX formation and in-cylinder temperature decrease with increase in the EGR rate. Further, CFD simulation is carried out to find optimum injection timing for bioethanol-diesel blends (0-30% ethanol). Optimum injection timing is obtained for maximum ITE. Obtained CFD results are validated with experimental data available in literature and found good agreements.Several second generation biofuels (e.g., n-butanol) are also promising alternative to diesel fuel. The experimental and CFD simulation is carried out to estimate the performance, combustion and exhaust emission characteristics of n-butanol-diesel blends (0 to 30%) for various injection timings and various EGR rates using modern twin-cylinder, four-stroke, CRDI engine. Experimental results reveal the increase in brake thermal efficiency (BTE) for n-butanol-diesel blends. Attention is also focused to counter plastic waste disposal problem and to find alternate fuel to diesel by waste to energy retrieval. Present range of investigation evaluates the prospective use of waste plastic oil (WPO) as an alternative fuel for diesel engine. Experiments are conducted for various injection timings and for different EGR rates. Combustion, performance and tail pipe emissions of CRDI engine are studied. The NOx, CO and soot emissions for waste plastic oil-diesel blends are found more than neat diesel. To reduce NOx, EGR is employed which results in reduction of NOx considerably. Brake thermal efficiency (BTE) of blends is found to be higher compared to diesel. The higher NOx emitted by engine operated with WPO-Diesel blends are treated by multiple injection strategies. Experiments are carried out for various pilot injection timings and different main injection timings. The remarkable reduction in nitrogen oxide is observed by retarding main injection timing and injecting more fuel in pilot injection compared to single injection.