AN EXPERIMENTAL INVESTIGATION ON THE PERFORMANCE, COMBUSTION AND EMISSION CHARACTERISTICS OF CI DIESEL ENGINE AT VARIOUS COMPRESSION RATIO WITH DIFFERENT ETHANOL-BIODIESEL BLENDS

In the present scenario of increased industrialization and transportation in the world leads to increased consumption of fossil fuels which in turns leads to depletion of fossil fuels at a faster rate. Fossil fuels combustion is the dominant source for greenhouse gases and global warming. In view of energy crisis raised in 1970’s and environmental concern, many researches are directed towards search of alternative fuels which can replace use of fossil fuels there by reducing pollution. In developing countries like India which is agriculture land the promising bio-fuels are biodiesel and ethanol which are produced from various renewable feedstock like sugarcane, corn etc. and they are also less hazardous to environment because of lower emission property. Ethanol blends results in decreased emissions of hydrocarbon (HC), carbon monoxide (CO) and particulates matter but increase in nitrogen oxides (NOx). Addition of ethanol leads to reduction of biodiesel viscosity. This paper represents variations in the engine parameters like performance, combustion and emission of single cylinder four stroke CI diesel engine by using various compression ratios such as 17.5:1, 18.5:1 and 19.5:1. Experimental research has been conducted with four proportions ethanol, namely E10, E20, E30 and E40. Ethanol-biodiesel mixture mixed with 2% emulsifier 1% diethyl carbonate and 1% ethyl acetate to maintain similarity and to avoid phase separation. Ethanol subjected to high compression ratio has been used to increase brake thermal efficiency (BTE). Increased compression ratio also improves the combustion and performance of the diesel engine.


INTRODUCTION
Indian oil imports account for nearly 130 billion $ every year which accounts for nearly 73% of the overall usage. This largely import dependent product critically effects our growing economy since its price fluctuates due to several factors such as political and social scenarios in the exporting countries. Emerging third world countries such as China and developed countries such as the United States and most of the western European countries survive on the same sources.
While this skewed global supply-demand economics is creating a continuous increase in the oil prices, the rural Indian setting which is developing at a slower rate than most of the metropolitan areas is being worst hit due to the increased prices. Several schemes have been initiated by the Indian government to use renewable fuels obtained from biological wastes to minimize the dependency of foreign oil. Nearly all the production crops in India have a crop to residue ratio of around 35%, implying that nearly 65% of the crops are available for renewable energy production. Substantial researches are conducted on the usage of biodiesel in the engines, but only 20% blends (B20) are currently suitable with the current diesel engine designs due to efficiency, durability and emissions issues.
Finding an alternative fuel like methanol, butanol and ethanol is directly benefit for industries, automobiles, farmers and it helps to prevent the issues like greenhouse gas effects. Indeveloping countries like India bio-fuels are economically less expensive than other fossil fuels. Therefore, it provides a scope for research work. There are two types of ethanol used in automotive application, one is anhydrous ethanol and the other is hydrous ethanol of which anhydrous ethanol contains a maximum of 0.7% water on weight basis and hydrous ethanol contains up to 7.4% of water on weight basis when measured at 20 0 C. Hydrous ethanol emits less CO2 compared to biodiesel mass anhydrous [1].
The purpose of this paper is an attempt made to review the previous studies to look into future Adding solvents like 2% emulsifier agent prevents the separation and ensure the similarity. The increased compression ratio has a similar effect as raising the inlet air temperature which results in gradual increase in the intake pressure. The compression ratio modifications effects ignition timing, final temperature and pressure at the end of the compression process [2]. Compression ratio is raised up to 19.5:1 with the help of higher latent heat of vaporization, higher auto ignition temperature which improves of the efficiency of the engine [3]. The mean BTE of engine is increased more than 33%, when the compression ratio is raised gradually from 18 to 20. By increasing the CR up to the maximum value which results in improvement of the effective pressure by using hydrous ethanol, while reduction of Mean Effective Pressure (MEP) and Break Thermal Efficiency (BTE) occurs by increasing compression ratio [4]. Increased CR leads to high cylinder temperature which causes faster evaporation of ethanol blends resulting in improvement of the combustion [5].
Based on previous researches and on reviews, the alternative energy fuels were found to be natural gas, alcohol, dimethyl ether and biodiesel. In developing countries like India which is agriculture land, ethanol and biodiesel are the promising alternative fuels which are produced from agriculture feedstock with low cost. It is a highly oxygenated fuel extracted from vegetable edible oils like sunflower, soya bean, palm, rapeseed, peanut etc. produced by process of transesterification. The high cetane number of biodiesel than diesel improves it combustion performance. The other additive advantages of biodiesel are low emission levels, increased lubricity, better combustion efficiency, easy biodegradability and low toxicity level. Vegetable oils are highly viscous and low heating value so it cannot be used directly and also increases carbon deposits [6]. To decrease emission rate and viscosity additives are used [7]. It is stated that nonlinear decrease in viscosity occurs by increasing alcohol contents. Addition of ethanol to biodiesel results in various changes in physical and chemical properties of biodiesel fuel [8]. The properties of various fuels are shown in Table.1

Fig.2. Photograph of Experimental Setup of Test Engine
The initial arrangements of the system are properly checked and test fuel is filled in the fuel tank. The Technical Specifications of the Test Engine are represented in Table .2

Impact on Brake Thermal Efficiency (BTE)
The effect of Ethanol and Biodiesel blends on Break Thermal Efficiency with Break Power at various compression ratios are represented in the Fig.3. Brake thermal efficiency is heat engine brake power, which helps in evaluating how engine converts fuel heat energy into mechanical energy. Incomplete combustion occurs with higher ethanol proportion at low compression ratio, due to longer ignition delay. Applying increased load for same proportion of ethanol results in increased BTE. But increased ethanol proportion leads to decreased BTE because ethanol is having low calorific value, so to generate same power additional fuel is required. By increasing CR and engine load results in decreased ignition delay and combustion period of ethanol. Rich mixture at high compression ratio of 19.5 and high engine load subjected to high combustion temperature increases oxygen kinetics in ethanol leading to increased break thermal efficiency (BTE). Increasing compression ratio improves power generation.  Increased ethanol proportion increases H/C ratio resulting in increased NOx emissions.
Increasing the compression ratio and at high load reduce NOx for 10% ethanol and neat biodiesel due to the primary combustion resisting of the engine knock. At higher CR, NOx emissions increase by 10%, 12% and 40% for E20, E30 and E40 respectively.