Combustion and performance evaluation of a diesel engine fueled with biodiesel produced from soybean crude oil

Abstract

In this study, the biodiesel produced from soybean crude oil was prepared by a method of alkaline-catalyzed transesterification. The important properties of biodiesel were compared with those of diesel. Diesel and biodiesel were used as fuels in the compression ignition engine, and its performance, emissions and combustion characteristics of the engine were analyzed. The results showed that biodiesel exhibited the similar combustion stages to that of diesel, however, biodiesel showed an earlier start of combustion. At lower engine loads, the peak cylinder pressure, the peak rate of pressure rise and the peak of heat release rate during premixed combustion phase were higher for biodiesel than for diesel. At higher engine loads, the peak cylinder pressure of biodiesel was almost similar to that of diesel, but the peak rate of pressure rise and the peak of heat release rate were lower for biodiesel. The power output of biodiesel was almost identical with that of diesel. The brake specific fuel consumption was higher for biodiesel due to its lower heating value. Biodiesel provided significant reduction in CO, HC, NO_x and smoke under speed characteristic at full engine load. Based on this study, biodiesel can be used as a substitute for diesel in diesel engine.

Introduction

The invention of internal combustion engine and subsequent developments in engine technology led to widespread exploitation of the petroleum reserves, which were being depleted at a rapid rate. Moreover, the combustion of these fuels has polluted environment. Many researchers have concluded that biodiesel holds promise as an alternative fuel for diesel engines. Biodiesel is oxygenated, biodegradable, non-toxic, and environmentally friendly. It consists of the alkyl monoesters of fatty acids from triacylglycerols, and can be produced from vegetable oils, animal fats, and waste restaurant grease [1], [2], [3], [4].

A lot of research work has been carried out to use biodiesel in compression ignition engine. Schumacher et al. [5] studied a model 6V92TA diesel engine fueled with blends of 10, 20, 30 and 40% soydiesel/diesel fuel. The engine was tested on the basis of the Environmental Protection Agency (EPA) heavy duty engine test cycle in an EPA certification test cell. The results indicated that engine fueled with soydiesel/diesel fuel blends reduced particulate matter (PM), total hydrocarbons(THC) and carbon monoxide (CO), while increased nitrogen oxides (NO_x). The optimum blend of biodiesel and diesel fuel was a 20/80 biodiesel/diesel fuel blend. Chang et al. [6] studied the effect of using blends of methyl and isopropyl esters of soybean oil with No.2 diesel fuel at several steady-state operating conditions in a four-cylinder turbocharged diesel engine. Fuel blends that contained 20, 50 and 70% methyl soyate and 20 and 50% isopropyl soyate were tested. Both methyl and isopropyl esters provided significant reductions in PM compared with No.2 diesel fuel. A blend of 50% methyl ester and 50% No.2 diesel provided a reduction of 37% in the carbon portion of the particulates and 25% in the total particulates. The 50% blend of isopropyl ester and 50% diesel No.2 diesel fuel gave a 55% reduction in carbon and a 28% reduction in total particulates. Emissions of CO and unburned HC were also reduced significantly. NO_x was increased by 12%. Mustafa et al. [7] used a John Deere 4045T four-stroke, four-cylinder, turbocharged direct-injection diesel engine to compare the exhaust emissions of the high-oleic soybean oil biodiesel with the standard conventional soybean oil biodiesel and diesel fuel. They noted a significant reduction in NO_x emissions for the high-oleic soybean biodiesel and no significant differences in unburned HC and smoke emissions. Mustafa et al. [8] compared the combustion characteristics and emissions of two different petroleum diesel fuels (No.1 and No.2) and biodiesel from soybean oil in a four-cylinder turbocharged DI diesel engine at full load at 1400 r/min engine speed. The result showed that biodiesel provided significant reductions in PM, CO and unburned HC, but NO_x increased by 11.2%. Biodiesel had a 13.8% increase in brake specific fuel consumption (BSFC) due to its lower heating value. However, No.1 diesel fuel gave better emission results. NO_x and BSFC reduced by 16.1% and 1.2% respectively. Senatore et al. [9] analyzed the combustion and emissions of a turbocharged DI diesel engine fueled with a mixture of rapeseed methyl ester and diesel fuel. Biodiesel produced significant reductions in the CO and smoke emissions and had higher NO_x emission. In case of using biodiesel, heat release always took place before top dead center (TDC) compared with diesel fuel. This led to a similar advance in the variation rate of the mean gas temperature in the cylinder which resulted in a different thermal history of the burnt gas. This behavior consistently determined higher peaks in the mean temperatures reached in the combustion chamber and the higher concentrations of NO_x. Chang et al. [10] investigated the atomization and combustion characteristics of biodiesel blended fuels in a common-rail diesel engine by using a spray visualization system and phase Doppler particle analyzer. They showed that the kinematic viscosity, surface tension, and cetane number of biodiesels such as unpolished rice oil and soybean oil became higher as the mixing ratio of the biodiesel increased. There was little difference in the spray tip penetrations according to the mixing ratio of the biodiesel. The ignition delay became shorter and the peak combustion pressure was higher with the increase of the mixing ratio. HC emissions can be reduced up to 55%by using biodiesel blended fuels, whereas NO_x emissions were increased. The oxygen in the biodiesel promoted the combustion process and increased the combustion temperature.

The fuel properties of biodiesel affect the engine performance and emissions, since it has different physical and chemical properties from diesel fuel. If this fuel is used in the diesel engines without any modification, more research is required about the properties of biodiesel and its effects on the combustion and the fuel system. In this study, the biodiesel from a soybean crude oil was produced by a method of alkaline-catalyzed transesterification. The properties, performance, emissions, combustion characteristics of a diesel engine were investigated by using biodiesel and diesel.