Internal Combustion Engine(ICE); Department of Mechanical and Industrial

Internal Combustion Engine (ICE)

              In general ICE is a heat engine and this can be defined as: “ A heat engine is a device which converts the chemical energy of a fuel into thermal energy” Such thermal energy is used to produce mechanical energy at the output shaft.

1. Comparison of ICE & External combustion engine ECE

            ICE                                                                                   

1. High max efficiency 2. Low first cost 3. Absence of large heat exchangers 4. Efficient cooling sys. 5. Effective cycle temperature control 6. Practical in mobile application 7. Exhaust heat energy utilization.

            EEC

1. Wide variety of fuel used
2. High staring torque
3. Almost free vibration engine.
4. Practical in a very large power unit
5. Practical in stationary application

        The conversion process of the chemical energy in a fuel into mechanical energy at the output shaft can be explained as follows: 1. Chemical energy of fuel is converted to thermal energy by oxidation with air (O2) in the combustion chamber. 2. Thermal energy raises the temperature and pressure of the gases within the engine cylinder. 3. High pressure gases expands against the resistance of engine mechanism and linkage. 4. The expansion process (power) forces the engine mechanism to reciprocate (piston) and rotate (crank). 5. Piston reciprocating ups and downs causes the crankshaft to rotate giving the output shaft a rotational torque.       Engines can be classified in many different ways, as they have many attributes, whereby making them capable of meeting a variety of needs and requirements. 

      The followings are the most used methods of engine classification: 

1. cylinder numbers & arrangement 2. engine cycles 3. type of ignition 4. valve position & location 5. cam shaft properties 6. engine speed 7. method of air & fuel supply 8. fuel used 9. cooling system 10.application 

      There are so many parts that constitute an internal combustion engine, which makes it a very complex system. Whereby, each part must act in a perfect synchronization with the others to make up: 

-a well defined machine -a well balanced operation -a well established timing            Most IC engines , both SI & CI, operates on either four or two stroke cycle, where: **stroke–is piston travel between the two dead centers **cycle–is a process to be completed once and continue to repeat itself in a constant duration. Therefore 4-stroke cycle requires pistons travel 4 times between top & bottom dead centers ,while the 2-stroke cycle requires pistons travel 2 timesThe main types of cycles to be considered are as follows : • 4-stroke SI engine cycle • 4-stroke CI engine cycle • 2-stroke SI engine cycle • 2-stroke CI engine cycle       4-stroke SI engine cycle Comprises of four piston stroke to complete one operational cycle through two revolutions of the crankshaft: 1. Induction stroke 2. Compression stroke 3. Power stroke 4. Exhaust stroke4-stroke CI engine cycleThese are similar to 4-stroke SI engine cycle with the following exceptions : 1. Induction -similar to SI except that only air is admitted without fuel. 2. Compression –similar to SI except that only air is compressed, and fuel will be added near the end of this stroke. 3. Power –after combustion, power stroke is similar to SI 4. Exhaust –similar to SIEmissions Four major emissions produced by IC engines : ** unburnthydrocarbon (HC) due to rich mixture of air/fuel **carbon monoxides (CO) not enough O2 to form CO2 ** nitrogen oxides (NOx) excess O2 and high combustion temperature ** solid particulates carbon particles as black smoke or soot  Methods to reduce engine emissions Two methods are generally used to reduce engine emissions and pollution rate : 1. Improve engine and fuel technology to obtain better combustion process. 2. Exhaust after treatment system Using thermal and catalytic converters that promote chemical reaction in the exhaust to convert harmful emission to acceptable forms such as (CO2, H2O ,N2)Discussion1.  ICE is a heat engine that covert chemical energy in fuel into mechanical work at the output shaft. 2. Most ICE are reciprocating type, whereby pistons reciprocate back and forth inside the cylinder. 3. Important technological inventions that influence the development of ICE are: **discovery of crud oil resulted in the development of reliable fuel appropriate for ICE use. 4. Two methods for engine emissions reduction: -Engine and fuel modification -Exhaust after treatment system

ICE

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