PERFORMANCE, EMISSION AND COMBUSTION STUDIES OF A MODIFIED VEGETABLE OIL IN A COMPRESSION IGNITION ENGINE

Abstract

The Indian transportation sector relies heavily on the diesel operated compression ignition engines. However, the combustion of diesel produces greenhouses gases which are a major threat to the environment as well as the humans. Alternatives to diesel are gaining importance for operating the engine as they can curb the greenhouse gases and are a key for addressing the energy security. One such alternative is used cooking oil, which the world, India in particular is generating in large quantities. The government of India is now emphasizing on the conversion of the used cooking oil into biodiesel. However, many studies show that the biodiesel cannot completely replace diesel due to its inherent issues. The biodiesel is produced from the used cooking oil by the transesterification method. Another method, namely hydroprocessing can also convert the used cooking oil into a fuel with properties closer to diesel. In the present research, the used cooking oil was converted to diesel like fuel by using the hydrotreating method and experiments were carried out on an engine to study the effect of the fuel on its performance and emission. The research was carried out in four phases. In the first phase, the hydrotreated oil was produced from the used cooking oil in the presence of a ruthenium based catalyst in a batch reactor. The reaction parameters namely reaction temperature, hydrogen pressure and reaction time were varied. Design of experiments were used for optimizing the process parameters. The Taguchi method was selected as it reduces the number of experiments which saves time and money. The aim was to increase the conversion percentage and diesel like fuel selectivity and reduce the naphtha selectivity. Since multi-objective optimization was required, Fuzzy logic was incorporated. The optimized parameters were 360°C reaction temperature, 40bar initial reaction pressure and 200min reaction time. Confirmation experiment was Performance, Emission and Combustion Studies of a Modified Vegetable Oil in a Compression Ignition Engine vii carried out using these parameters and the conversion efficiency and diesel like fuel selectivity was 89.7% and 88.2%, respectively. The physico-chemical properties, evaporation temperature, ignition probability and Sauter mean diameter of the blends of the hydrotreated oil and diesel were studied in the second phase. The GC-MS profile of the pure hydrotreated oil shows that the fuel has straight carbon atoms in the range of C11 to C20 and heptadecane is the predominant hydrocarbon. Properties like viscosity, density, calorific value, flash point, etc. were measured and found to be within the limits of ASTM standards. The fuels were also stored for a period of one year to study their stability in terms of density, viscosity and calorific value. The properties of the stored fuel changed slightly with time and their rate of change was also low. The hydrotreated fuel was mixed with diesel in various proportions and engine tests were carried out in the third phase. The results show that the brake thermal efficiency decreases with increase in the hydrotreated fuel share in the blend. The heat release for the blends starts earlier than diesel due to higher cetane number and the peak heat release is also lower than diesel. The HC, CO and smoke emissions for the test blends decreases up to 30% blend, further increase in the blending of hydrotreated oil resulted in increase in the emissions. The NO emissions were lower than diesel for all the test samples. The maximum reduction in NO (neat), HC (30% blend), CO (30% blend) and smoke emissions (30% blend) is 23.2%, 14.4%, 13.83%, and 13.3%, respectively. It the third phase of testing, it was observed that 30% blend of hydrotreated oil resulted in lowest emissions but the thermal efficiency was low. The thermal efficiency with 20% blend of hydrotreated oil was higher than 30% blend but the emissions with 20% blend were higher. To improve the shortcomings of the two samples addition of Performance, Emission and Combustion Studies of a Modified Vegetable Oil in a Compression Ignition Engine viii waste cooking oil biodiesel to the two samples was explored. Therefore, in the last phase, experiments were carried out by blending waste cooking oil biodiesel (5%, 10% and 15% on volume basis) in 20% and 30% blend of the hydrotreated oil. The results show that the heat released increases with the biodiesel addition on account of higher ignition delay but its starts earlier than diesel and its maximum value is still lower than diesel. The brake thermal efficiency of the biodiesel blended fuels increases and as the percentage of biodiesel increases the thermal efficiency increases. Among the blended fuels, the maximum thermal efficiency was observed to be 30.96% with 15% biodiesel mixed in 20% hydrotreated oil and 65% diesel. The lowest HC, CO and smoke emissions at full load were observed to be 1.73g/kWh, 24.02g/kWh and 49.2% respectively with 15% of biodiesel mixed in 30% hydrotreated oil. Among the biodiesel blends, the lowest NO emission is observed to be 3.61g/kWh with 5% of biodiesel mixed in 30% hydrotreated oil, whereas highest NO emission (3.98g/kWh) is observed with 15% of biodiesel mixed in 20% hydrotreated oil.