Hello dear,
If you encounter a phrase like 2.0 litres, this refers to the engines capacity. This is the combined capacity of all the engines cylinders. Typical modern engines have three, four, six or sometimes eight cylinders.

So a 2.0-litre four-cylinder engine will have a capacity of 500cc in each of its cylinders.

Each piston moves up and down inside its cylinder. The space it moves through is called the combustion chamber. This is where fuel is burnt by the engine to produce power  the explosive force caused by the fuel burning causes the pistons to move.

If a car is described as a 2.0-litre, this means the engines combustion chambers allow roughly 2,000cc (two litres) of fuel and air to be burnt.

If this engine is running at 3,000rpm, that means that every piston in the engine can burn 500cc of fuel and air 3,000 times a minute. The more air and fuel an engine can burn, the more power it usually produces.

As a result of advances in engine technology some of todays smaller engines are able to produce more power than certain bigger, more old-fashioned engines.