PERFORMANCE AND COMBUSTION CHARACTERISTICS OF DIESEL ENGINE: INTRODUCTION

INTRODUCTION

The rapid depletion of petroleum fuels and their ever increasing costs have lead to an intensive search for alternate fuels. The most promising substitutes for petroleum fuels are alcohols. So, it is high time that scientists developed an alternate and renewable fuel that would run on the existing engines without many modifications and also one that would cater to the ever increasing power needs of the countries and domestic market. It is well known fact that small amount of energy is left for useful purpose in engine remaining energy is wasted through friction, heat loss through coolant and heat loss through exhaust gas. Hence the concept of the LHR engine is to minimize the heat loss to the coolant, by providing resistance in the path of heat flow to the coolant thereby gains the heat energy. Several methods adopted for achieving LHR to the coolant are i) using ceramic coatings on piston, liner and cylinder head ii) creating air gap in the piston and other components with low-thermal conductivity materials like superni, cast iron and mild steel etc.

Investigations were carried out on bio-diesel by many researchers by coating with low thermal conductivity materials like ceramics on engine components like cylinder head, cylinder liner, valves and piston crown, and it was reported that ceramic coated engines improved specific fuel consumption (SFC) and decreased pollution levels. However, low degree of insulation provided by these researchers was not able to burn effectively high viscous crude vegetable oils. Creating an air gap in the piston involved the complications of joining two different metals. Air gap was created [6] in the piston by screwing the crown made of low thermal conductivity material, nimonic (an alloy of nickel) to the body of the piston, by keeping a gasket, made of nimonic, in between these two parts. But investigations are restricted to pure diesel operation. It was reported from these investigations that SFC was improved and pollution levels of smoke decreased at advanced injection timing. Experiments were also conducted on conventional engine (CE) with either with blends of vegetable oil and diesel or with blends of bio-diesel and diesel and it was reported that these blends improved the efficiency of the engine and decreased the pollution levels. Experiments were also conducted [11] on waste fried vegetale oil collected from restaruents and reported CO and smoke emissions were reduced using preheated waste frying oil at 135°C. Investigaons were conducted with vegetabl oils and reported that all emissions parameters were within maximum limits and concluded safer use as an alternate fuel.on vegetable oils. Compression ratio was also increased with CE with vegetable oil based bio-diesel and it was reported that poor performance was obtained at lower compression ratio and performance of the engine was improved at compression ratio of 18:1. Experiments were conducted on vegetable oil based bio-diesel on CE and reported improvement in BTE, exhaust emissions but increased NOx emissions and slight increased brake specific fuel consumption (BSFC). There are many techniques available to induct ethanol into the engine, out of which carburetion technique is simple. Carbureted ethanol was used in CE and in LHR engine with air gap in the insulated piston and insulated liner and vegetable oil was injected in conventional manner and reported that exhaust gas emissions decreased with LHR engine, when compared with pure diesel operation on CE as high heat generated in the combustion space due to adiabatic conditions improved alcohol combustion. However, in their investigations, combustion characteristics and performance parameters were not reported. Vegetable oils have cetane number comparable with diesel fuel, but they have high viscosity and low volatility. Alcohols have low cetane fuels, though they have got high volatility. In order to take advantage from high cetane number and high volatility, both vegetable oils and alcohols have to be used in LHR engine.

The present paper attempts to evaluate the performance of LHR engine, which contains air gap piston and air gap liner with crude jatropha oil with carbureted ethanol with varying engine parameters of change of injection pressure and injection timing and compared with pure diesel operation on CE at recommended injection timing and injection pressure.