03-03-2011, 12:58 PM
presented by:
SATYENDRA VERMA
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FUEL INJECTION PROCESS
Introduction
The internal combustion engine is an engine in which the combustion of a fuel (normally a fossil fuel) occurs with an oxidizer (usually air) in a combustion chamber. In an internal combustion engine the expansion of the high-temperature and -pressure gases produced by combustion applies direct force to some component of the engine, such as pistons, turbine blades, or a nozzle. This force moves the component over a distance, generating useful mechanical energy.
The term internal combustion engine usually refers to an engine in which combustion is intermittent, such as the more familiar four-stroke and two-stroke piston engines, along with variants, such as the Wankel rotary engine. A second class of internal combustion engines use continuous combustion: gas turbines, jet engines and most rocket engines, each of which are internal combustion engines on the same principle as previously described.
The internal combustion engine (or ICE) is quite different from external combustion engines, such as steam or Stirling engines, in which the energy is delivered to a working fluid not consisting of, mixed with, or contaminated by combustion products. Working fluids can be air, hot water, pressurized water or even liquid sodium, heated in some kind of boiler.
A large number of different designs for ICEs have been developed and built, with a variety of different strengths and weaknesses. Powered by an energy-dense fuel (which is very frequently petrol, a liquid derived from fossil fuels), the ICE delivers an excellent power-to-weight ratio with few disadvantages
Four-stroke cycle (or Otto cycle)
1. Intake
2. Compression
3. Power
4. Exhaust
As their name implies, operation of four stroke internal combustion engines have four basic steps that repeat with every two revolutions of the engine:
1. Intake
o Combustible mixtures are emplaced in the combustion chamber
2. Compression
o The mixtures are placed under pressure
3. Combustion (Power)
o The mixture is burnt, almost invariably a deflagration, although a few systems involve detonation. The hot mixture is expanded, pressing on and moving parts of the engine and performing useful work.
Exhaust
o The cooled combustion products are exhausted into the atmosphere
Many engines overlap these steps in time; jet engines do all steps simultaneously at different parts of the engines.
Combustion
All internal combustion engines depend on the exothermic chemical process of combustion: the reaction of a fuel, typically with oxygen from the air
Functional requirement of an injection system
For a proper running and good performance from the engine, the following requirement must be met the injection system
1. Timing the injection of the fuel correctly in the cycle so that maximum power is obtain ensuring fuel economy and clean burning.
2. Proper control of fuel injection so that the proper heat release pattern is achieved during combustion.
3. Proper atomization of the fuel is obtained.
4. Proper spray pattern to ensure rapid mixing of fuel and air.
5. Uniform distribution of the fuel droplet throughout the combustion chamber.
6. To supply equal quantities of the metered fuel to the entire cylinder in case of multi cylinder engine.
7. No tag during beginning and end of injection.
8. Accurate metering of the fuel injection per cycle. This is very critical due to the fact that very small quantity of fuel being handled.
9. Metering errors may cause drastic variation from the desired output. The quantity of the fuel metered should vary to meet changing speed and load requirements of the engine.
10. The rate of injection should be such that it the desired heat release patterns.
Types of injection system
Diesel injection system can be divided into two basic types.
1. air injection
2. solid injection
Air injection
The fuel is metered and pumped to the fuel valve by a camshaft driven fuel pump. The fuel valve is opened by means of a mechanicals linkage operated by the camshaft which controls the time of injection. the fuel valve is also connected to a high pressure air line fed by a multi-stage compressor which supplies air at a pressure of about 60 to 70bar.
When the fuel valve is opened the blast air sweeps the fuel along with it and a well atomized fuel spray is sent to the combustion chamber.
