Experimental investigation of the combustion, performance and emission parameters of a compression ignition engine using blends of vegetable oil and diesel fuel

Abstract

Rapid depletion petroleum reserves, gradual rise in the oil prices and the wide-spread pollution caused by these fuels have led to a great concern worldwide to develop better and cleaner strategies. This global concern has promoted research to find substitutes to fossil fuels with considerable efficiency and lower emissions to cater with the stricter emission norms as set by various governments. Diesel engines are well established today, as the main power train solution for trucks and other relevant heavy duty vehicles. Thus, developing substitutes to diesel for efficient and clean application in these diesel engines is the need of the day.

Vegetable oils are very good alternative fuels and have great potential for use in internal combustion engines because of their abundant availability, renewable nature and lower emissions. Many vegetable oils have been used in compression ignition engines with fuel modification or engine modification. Since, the vegetable oils have higher viscosity which results in poor atomization and poor combustion, so they are blended with diesel to obtain a less viscous mixture. Polanga oil, non edible oil by nature is available in a few states of India like Orissa, Kerala, and Tamil Nadu etc. Polanga oil is characterised with a comparable Calorific Value to diesel, higher cetane number but a greater viscosity. An experimental investigation was made to evaluate the combustion, performance, and emission characteristics of a diesel engine using blends of Polanga oil and diesel. Polanga oil of 10%, 20%, 30%, 40%, 50% and 60% on a volume basis was blended with 90%, 80%, 70%, 60%, 50%, and 40% diesel fuel respectively and used as fuel in an air-cooled, direct injection, CI engine. The combustion, performance and emission parameters were thus studied and presented in the present work. The experimental results showed that PD30 was the optimum blend with marginal rise in the combustion and performance parameters than diesel fuel. But, the hydrocarbon and carbon monoxide emissions were found to be higher than diesel fuel, though the Nitric oxide emissions were lower than that for diesel fuel. This potentially could have resulted due to incomplete combustion of the Polanga –diesel blends in the engine resulting in higher HC and CO emissions but lower NO emissions due to lower cylinder temperatures.

To reduce the emissions of the optimum blend further, the fuel injection pressure was varied from 200 bar to 240 bar in steps of 10 bar to aid in better combustion of the fuel. The combustion, performance and emission characteristics of the single cylinder, air cooled, direct injection, diesel engine with optimum Polanga-diesel blend at varying injection pressures were studied and presented in the current work. It was observed that with increase in the injection pressure, combustion, performance and emission parameters showed better results till an optimum injection pressure and decreased thereafter. From the experiments, it was concluded that 220 bar injection pressure was the optimum value for PD30 blends since it showed better efficiency, lower ignition delay and lower HC and CO emissions as compared to diesel fuel operation. But, the Nitric oxide emissions were found to be higher than that of the standard diesel fuel operation values.

In an attempt to reduce the NO emissions, Exhaust gas was recirculated to the engine and mixed with fresh air-fuel mixture to decrease both the flame temperature and the oxygen concentration in the combustion chamber. In the present work, the EGR was applied to the diesel engine (as already used in previous investigations) with the optimum Polanga –diesel blend (PD30) at optimum injection pressure (220 bar). The exhaust gas recirculation was carried out with variable rates (10%, 20% and 30%) and the combustion, performance and emission parameters of the diesel engine were studied. It was observed that among various rates, 30% EGR resulted in a marginal rise in the performance and combustion of the engine and a simultaneous decrease in the NO and smoke formation.

In the present work, attempt has been made to identify a vegetable fuel as a better substitute to diesel fuel. In the process, Polanga oil was chosen for blending with diesel fuel owing to its comparable calorific value with diesel and greater cetane number. The combustion, performance and emission parameters of the single cylinder, direct injection, air-cooled diesel engine fuelled with various Polanga-diesel blends were studied and PD30 was identified as the optimum blend. Further, the effect of injection pressure on the performance of the diesel engine was studied and 220 bar was adjudged as the optimum injection pressure with better performance and combustion parameters but higher NO emission. To reduce the NO emissions, EGR at various rates (10%, 20% and 30%) was applied and EGR at 30% was concluded as the optimum rate of EGR.