COMBUSTION ANALYSIS OF WASTE OIL BASED BIODIESEL FUELED DI DIESEL ENGINE

Abstract

Biodiesel is renewable and biodegradable fuel having the properties near to conventional diesel fuel. It is an eco-friendly fuel containing no sulphur, no aromatics and also having a higher content of oxygen. According to American Society for Testing and Materials (ASTM), Biodiesel is “Mono alkyl ester of long chain fatty acids produced from renewable lipid feedstocks, such as vegetable oils and animal fats, for the use in CI engines”. The biodiesel has the potential to replace the conventional diesel. The higher cost of biodiesel as compare to diesel fuel is the biggest hurdle. The higher cost is mainly includes high production cost due to limited availability and higher cost of feed stock. So, for biodiesel production the waste vegetable oils (waste cooking or fried oils) can also be used. In the present work the combustion, performance and emission characteristics of biodiesel and its blends were analysed and compared with diesel to optimize the engine operating and injection parameters. Biodiesel was produced by transesterification using mechanical stirring method. The composition i.e. 6:1 molar ratio of methanol to oil by volume was selected. Potassium hydroxide (KOH) 1 % by weight was taken as a catalyst and the reaction temperature was kept 60-70 °C for 2 hrs. After the reaction glycerol present in oil was allowed to settle down and was separated using separating funnel. The conversion efficiency was about 89%. Here the properties of biodiesel were measured as per the ASTM standard number D6751. In the first study the influence of injection pressure on combustion, performance and emission of a CI engine fueled with waste cooking oil methyl ester was analysed. Firstly the experiments were carried out on diesel fuel at the rated injection timing 13.5⁰ BTDC and 2000 rpm speed. Then the fuel supply was switched to biodiesel mode. The measurements with biodiesel were started after some time when the engine attains a steady state condition. The engine load was varied from 25% to 100% (full load). The rated nozzle opening pressure was 225 bar which was varied in steps to 235 and 245 bars. The biodiesel fuel needs to be injected at higher pressure to improve the atomization of biodiesel. The injection pressure was increased by varying the spring tension in injector by adding an extra washer. The nozzle opening pressure was increased by 10 bar by adding one washer. In the analysis of combustion maximum Peak cylinder pressure was lower for biodiesel B100 than diesel due to lower heating values. The rate of heat release was lower for biodiesel B100 than diesel fuel because of the lower heating value. In case of biodiesel the combustion starts earlier than diesel engine due to shorter ignition delay of biodiesel. The combustion duration was more for biodiesel than diesel iv fuel. The maximum rate of heat release increases as the injection pressure increases. At higher injection pressure higher heat release rate was observed but rate of heat release was maximum for diesel. It was investigated from the performance analysis that the brake specific fuel consumption reduces with increase in load. BSFC increases with increase in fuel injection pressure. The reason of this increase is that due to the higher density of biodiesel, more amount of biodiesel is injected in combustion chamber to generate the same power. The brake thermal efficiency increases as the load increases. Brake thermal efficiency is reduced in case of biodiesel B100. The Brake thermal efficiency decreases with increase in fuel injection pressure. In emission analysis, CO, HC and Smoke emissions can be reduced by increasing fuel injection pressure. At the higher injection pressure 245 bar, better combustion of biodiesel fuel was observed. The increase in NO emission was also observed for B100 because of lesser soot formation. There is slight reduction in NO emission for higher injection pressure at 245 bar at full load. The increase in fuel injection pressure can be an effective method to enhance the combustion performance end emission characteristics of an engine fueled with pure biodiesel (B100). In the second chapter, comparison of combustion, performance and emission characteristics of diesel engine fueled with diesel and waste oil based biodiesel at different injection timings is made. In this study firstly the experiments were carried out on diesel fuel at rated injection timing 13.5⁰ BTDC and at rated injection pressure of 225 bar at various loads from 20% to full load. It was found from the literature that when the diesel engine was fueled with biodiesel without any modifications in injection timing, shows poor combustion. The reason for this is variation in fuel properties of diesel and biodiesel such as kinematic viscosity and density etc. The higher viscosity and density of biodiesel causes slight advancement in start of injection and start of combustion in terms of crank position. Hence experiments for the biodiesel were performed at the different injection timings from 13.5⁰ to 17.5⁰ BTDC. Peak cylinder pressure was lower with waste oil based biodiesel than that for diesel mainly due to lower calorific value of wco biodiesel. The peak cylinder pressure reduced with advance injection timing. Cylinder pressure was maximum for diesel and minimum for 17.5⁰ btdc. The brake specific fuel consumption decreases with load. Brake specific fuel consumption was minimum when the engine was fueled with diesel fuel. Bsfc was maximum for diesel and maximum for wco biodiesel at 13.5⁰ which reduces the on advancing the injection timing. The brake thermal efficiency increases as the load increases. BTE for the wco biodiesel was lower v than that for the diesel fuel. As the injection timing advances, BTE increases for the advanced injection timing. In case of waste oil based biodiesel maximum efficiency was for 17.5⁰ BTDC but lower than the diesel. In case of wco biodiesel CO, HC and Smoke emissions can be reduced by advancing fuel injection timing. The increase in NO emission was also observed for wco biodiesel because of lesser soot formation. This was mainly due to the higher oxygen content in biodiesel B100. There is slight reduction in NO emission for advanced injection timings at all loads. In the last study, engine operating and injection parameters were optimized using multiobjective optimization method. The five fuel blend ratios were selected as B0 (pure diesel), B25, B50, B75, B100 (pure biodiesel). Load was varied from 0 to 100% of full load by taking the variation of 20% in each step. Variation of speed was taken from 1300 to 2100 rpm at the difference of 200 rpm. Injection timing levels were selected from 11.5° BTDC to 19.5° BTDC with the difference of 2°. Standard injection timing for the test engine was 13.5° BTDC. The deteriorating performance of the engine with biodiesel and its blends is the result of poor atomization and vaporization of fuel in combustion chamber. The main cause of the poor atomization is poor injection characteristics affected by fuel properties like viscosity and the density. The main injection characteristics affected by the fuel properties are spray penetration, spray cone angle and sprat tip speed. Spray characteristics such as spray penetration and speed of spray tip increased with higher percentage of biodiesel in its blends. However the spray cone angle was reduced, it happened mainly due to poor atomization of fuel caused by higher viscosity of biodiesel. The possible reasons for the reduction in spray cone angle and increase in spray penetration of tip speed could be as follow: The spray penetration was longer with increase in blend percentage of biodiesel. This was mainly due to higher viscosity of biodiesel. The higher viscosity prevented the breaking of spray jet. The higher viscosity also causes poor atomization and results in larger size of spray droplets, this also results in higher momentum of droplets and less resistance against the forward movement of droplets. The spray cone angle decreased with increase in blend percentage of biodiesel. The spray cone angles increased, then decreased, and then remained stable. The main reason for this was mainly because the higher injection pressure caused the spray to spread around, which increases the cone angle. As the spray continued, droplets around the border became smaller and diffused easily; this also results in the reduction of spray angle. However, the lower injection pressure reduced the spray angle. Finally, the volatilized and nonvolatilized fuel reached a dynamic balance, and the cone angle then stabilized. There was a vi variation in spray tip speed due to the fluctuation in injection pressure inside the high-pressure pipeline. The previous pulsive process of the spray droplets caused the pressure in this region to be lower than back pressure, and the subsequent spray droplets were then able to move forward at high speed and collide with the previous spray droplets which may also have contributed to spray tip speed fluctuations.