samim khan

 Profile Answers by samim khan 

• Jan 26th, 2010

 

The si or spark ignition engine uses petrol as a fuel and the ci or compression ignition engine uses diesel as a fuel. Both the fuels has different compression ratio.

In si engine the compression ratio is 8-12:1.
In ci engine the compression ratio is 16-22:1.

So incase of si engine, the compression ratio is not sufficient for fuel to burn so a spark plug is used, whereas in ci engine, the compression ratio is so high that due to its internal heat the fuel is combusted so there is no need for a spark plug.

so the technology used in si engine is different from ci engine.

Hope I have answered your question.

d_tyro_22

 Profile Answers by d_tyro_22 

• Jan 27th, 2010

 

By the virtue of ignition and chemical properties of the fuel used (diesel or petrol), same technology can't be used for both the engines.

Diesel has lower self-ignition temperature than petrol.  Therefore flame-formation for diesel (in ci engines) is achieved by a temperature rise by compression only, where as petrol (in si engines) with comparatively higher self-ign temp needs an external spark for the same.

If the same technology of ci engine is to be employed for petrol, larger temp rise and thus a larger compression is needed, which in turn increases the surface area of piston, thus enormously increasing the size of engine.

senumama

 Profile Answers by senumama 

• Jan 27th, 2010

 

In SI engine the compression ratio is less so fuel can not reach it's self ignition state, for that spark plug is used i SI engine. in CI engine compression ratio is high so temperature goes high and fuel go ignite.

rakesh_ms

 Profile Answers by rakesh_ms 

• Aug 20th, 2010

 

The properties of both these fuels i.e., gasoline and diesel are different, Gasoline is less flamable than diesel.

ansi9164

 Profile Answers by ansi9164 

• Aug 23rd, 2010

 

Self ignition temp of petrol in higher then diesel so it requires much pressure for self ignition as compared to diesel, due to this reason CI is not
favorable in case of petrol engine.