Spark Ignition vs Compression Ignition | Compression Ignition Engines (CI engines) vs Spark Ignition Engines (SI engines)
Spark and compression ignitions are totally different mechanical technologies that are used in engines. Engines that use spark ignition technology are called as spark ignition engines (SI engines), and the others are known as compression ignition engines (CI engines). These two methods of ignition are used in engines in their combustion stroke. In order to ignite the fuel and get the thermal energy, the ignition should take place. In SI technology, electric spark is used to provide the ignition to a properly mixed air-fuel mixture, but in CI technology, the air is compressed to a higher temperature and that high temperature cause to an ignition.
Spark Ignition
Mainly spark ignition is used in the engines that work on otto cycles. The fuel used in a SI engine is Petrol. Because petrol is highly volatile, it is easily burned by a little spark. That is; more volatility means lower ignition temperature. So that for Spark Ignition technology aromatics are mostly preferred as the fuel, since they are more volatile than the alkanes and can burn at lower temperatures. In addition, when you use SI technology for an engine, the compression ratio required will be less (approximately 9:1), because of the high volatility of the fuel they use. At the same time, SI technology produces comparatively less smoke after the ignition. SI engines are smaller in size, as it does not want a larger combustion chamber. However, SI technology is comparatively dangerous since the air-fuel mixture is sent to the combustion chamber by compressing. In that case, if the temperature reaches the flash point (Ignition temperature) before the spark ignition, it can result in a detonation. Because, after the spark the temperature will increase further.
Compression Ignition
Unlike in SI technology, in compression ignition, it does not use a spark plug. The high temperature caused by compressing the air is sufficient for the ignition. CI engines work on diesel cycles. The fuel they use is diesel. Diesel has less self-ignition tendency, since it is less volatile. So that in CI technology, comparatively larger compression ratio will be obtained by the engine (approximately 20:1), and apparently, CI engines have more efficiency. What happens in CI is that the fuel is injected under pressure into the cylinder after the air is already compressed. Then the ignition will take place because of the temperature increase caused by the compression. However, the bad thing in CI technology is that the fuel is not fully burnt. So that, the exhaust gas will contain some unburned hydrocarbons. At the same time, in CI operation, comparatively more noise will be produce due to the compression process.
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What is the difference between Spark Ignition and Compression Ignition? • • Spark ignition uses petrol as the fuel, but Compression ignition uses diesel. • SI works on otto cycle while CI works on diesel cycle. • SI is used in petrol engines while CI is used in diesel engines. • CI has more efficient than SI. • CI produces more noise than SI when it works. • CI produces more hydrocarbons at the exhaust stroke of the engine than SI engines. • SI engine has a spark plug, but CI does not have one. • SI air-fuel mixture enters into the combustion chamber, but in CI, air and fuel enter separately in to the combustion chamber. • CI has higher compression ratio than SI. • SI is more harmful due to the pre-detonation things than CI.
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