IGNITION
COMPRESSION
CARBURETION

If you dont understand these three terms and their relation to the internal combution engine, you have some homework to do!
These are the three systems of any engine.

In order to understand how these systems power an engine, you must understand the four Strokes that complete one revolution of the engine's crankshaft (you know the part that turns linear[back and forth] motion into radial motion[Turning]).
the four Strokes are :
IGNITION
COMPRESSION
POWER
EXHAUST

in a two stroke cycle engine (glow), power and exhaust take place almost simotaneously. Also, compression and ignition also happen in the same stroke. That is why we label a glow engine a 2C (two [Stroke]Cycle).

A gas or spark ignition engine takes 1 stroke to do each job! That is why they have less power per given displacement. The power stroke happens 1 stroke out of 4.

Hope this info may help. But please look up the 3 systems and 4 strokes. Im sure others have explained them better
hope this helps!
PAT