PERFORMANCE, EMISSION AND COMBUSTION CHARACTERISTICS OF A BIODIESEL FUELLED DIESEL ENGINE

Abstract

India’s economy is essentially diesel driven, and diesel consumption is almost four to five times higher than that of gasoline. So, biodiesel has proved its utility as a promising renewable and sustainable alternative to the petroleum diesel in the last two decades. One of the main barriers for commercialization of biodiesel is the cost of biodiesel as it is commonly derived from vegetable oils. Hence, the use of low-cost oils as biodiesel feedstocks is very much essential. In this context, Government of India approved the National Policy on Biofuels in December 2009 to substitute 20% of mineral diesel consumption by biodiesel from non-edible oils. However, the ambitious plan of producing sufficient biodiesel to meet the mandate of 20 percent diesel substitution by the year 2017 has not been realized. Excessive reliance on Jatropha curcas as the only feedstock and the inability to produce sufficient quantity has been one of the major reasons for not attaining the mandate. In the light of the above, the present research deals with the comprehensive study of other potential alternative tree borne oil seeds; Sal (Shorea robusta) and Kusum (Schleichera oleosa) for biodiesel production. In India, both feedstocks are potentially available and grossly unexplored for biodiesel production. The main objective of this research work is to produce Sal methyl ester (SME) and Kusum methyl ester (KME) and carry out combustion, performance and emission studies in a small capacity diesel engine with these biodiesel. The research work has been divided into four major sections. In the first part, production of biodiesel (fatty acid methyl ester) from Sal oil and Kusum oil using either single-stage or two-stage transesterification was carried. A four factor central composite design (CCD) based on response surface methodology was employed for both single stage (esterification) and second stage(transesterification) processes to produce biodiesel from the high free fatty acid (FFA) vegetable oil. The process parameters like catalyst concentration, Performance, Emission and Combustion Characteristics of a Biodiesel Fuelled Diesel Engine Page vii reaction time, reaction temperature and methanol to oil molar ratio were taken as factors in the design. Based on the CCD designed test matrix, the experiments were carried out and the results were analysed. Kusum oil has high FFA content (approx 8%) therefore two stage transesterification was used whereas Sal oil has less than 2 % FFA, so single stage transesterification was employed. The optimum conditions for the acid catalysed esterification of Kusum biodiesel were 0.927 % catalyst concentration, 62.11°C reaction temperature, 67.82 minutes reaction time and 6.4 molar ratio. For the alkaline stage, 1.13 % catalyst, 63.18°C temperature, 79.2 minutes reaction time and 8.16 methanol/oil molar ratio; resulted in an optimal yield of 97.41% biodiesel. Based upon the optimum conditions, the confirmation tests were conducted and biodiesel yield achieved was 96.92% for Sal biodiesel and 96.5% Kusum biodiesel. In the second stage of the research work, fatty acid profile and various physicochemical properties of SME and KME were experimentally evaluated. The results of the Gas chromatography–mass spectrometry (GC-MS) study indicated that SME composition laid down between C-16 to C-20, where 61% saturated and 39% unsaturated of the total mixture whereas KME composed of C-16 to C-22 and it has 31% saturated and 69% unsaturated fatty acids. Properties like viscosity, density, calorific value, flash point, etc. were measured and found to be within the limits of ASTM standards. Presence of 61% saturated compounds of SME makes it highly susceptible to poor cold flow properties. On the other hand, KME has significant portion of unsaturated acids like oleic acid (C18:1) and eicosenoic acid (20:1). So Kusum biodiesel has poor oxidation stability. The third stage of the study is related to the evaluation of cold flow properties and oxidation stability of both biodiesel using additives. The chemical additives for the improvement in cold flow properties are synonymously referred to as pour point depressants Performance, Emission and Combustion Characteristics of a Biodiesel Fuelled Diesel Engine Page viii (PDD). Application of the PPDs showed improved cold filter plugging point (CFPP) for all the test fuels. Among all additives, CRISTOL showed best results for both biodiesels. Storage stability for one year has suggested that some of the physico-chemical properties of both the biodiesel (SME and KME) changed slightly with time. The rate of change of different physico-chemical properties was found to be lower for both the biodiesel with an additive. The fourth stage of the study comprised of fuel blend preparation, test rig development and study of the engine performance, exhaust emissions and combustion characteristics with biodiesel-diesel blends up to 40% and comparison of results with baseline diesel (D100). Various test fuels for the engine trials were Sal biodiesel (SME10, SME20, SME30 and SME40) and Kusum biodiesel (KME10, KME20, KME30 and KME40) with 10%, 20%, 30% and 40% volume wise substitution of D100 with biodiesel. The results indicated higher engine performance up to 20% blending of biodiesel in diesel as compared to baseline diesel. Other higher blends showed a marginal reduction in engine performance. Both biodiesel blends exhibited lower emissions of carbon monoxide (up to 63.77%), total hydrocarbon (up to 33.39%) and smoke opacity (up to 48%). However, emissions of oxides of nitrogen were increased with increase in biodiesel volume fraction in the test fuel. A notable observations of both the biodiesel were noticed in the combustion study that the trend of in-cylinder gas pressure and heat release rate (70.71 J/̊CA for KME 20)increases with increase in biodiesel volume fraction up to 20% volume of biodiesel. Further increase in volume fraction of biodiesel showed diminishing trends for both SME and KME biodiesel. At the same time decrease in pressure rise rate (13.5%) and ignition delay period was observed (25%)with increasing biodiesel content up 40 % in biodiesel-diesel blends as compared to the baseline results. With increase in volume fraction of SME and KME in the blend, ignition delay was reduced from 11°CA for D100 to 8.2°CA for SME40 and 8.3°CA for KME40. Another Performance, Emission and Combustion Characteristics of a Biodiesel Fuelled Diesel Engine Page ix notable observation was that cumulative heat release of SME10 and KME 10 were higher than other test fuels. As an outcome of an exhaustive engine trial and the subsequent analyses, it may be stated that Sal methyl ester and Kusum methyl ester are an excellent diesel engine fuel. Up to 20% blend of SME and KME with diesel may be used in any unmodified diesel engine with improved performance, emission (except NOx) and combustion characteristics.