Why do we need to compress air before combustion? Will it work without compression?
For petrol (gasoline) the liquid is above its flashpoint at all normal temperatures. This means that it gives off a vapor which makes an explosive mixture with air. So if you have a cylinder containing air and inject some of the liquid you can get an explosion when a spark is made. The injector or carburetor puts the liquid into contact with the air to get close to equilibrium quickly. All we need to do is therefore arrange enough pressure or suction to get the air into the combustion space.This also means that the liquid is a considerable fire hazard.By contrast, diesel fuel has a flash point well above ambient, so does not give an explosive mixture with air, and would not ignite in the spark engine. The ingenious thing about the diesel engine is that by compressing the mixture it heats up and in addition the concentration of oxygen increases, so that more power is possible. It heats it up to the point where it self-ignites without a spark.For petrol (gasoline) engines it is also possible to increase the power by putting in more fuel and also more air by compressing it. This is what is done with a turbo-charger.
Can a compressed air burn if ignited with electric spark?
What do you exactly mean by the process... If you mean the gas is compressed(liquified) and a arc is generated at this time, the inflammable gas will burn[Depending on circumstances] If you mean the gas is decompressed from its liquified form, it will ignite for sure. Or if you mean the gas is air, then if its compressed or in any state, it won't ignite at all...