differences between SI engines and CI engines?

Answer 1

In a CI (Compression Ignition) Engine, air is first injected and heated by compressing it in a cylinder, whereupon diesel fuel is then injected into the hot compressed air and the combustion in the cylinder is spontaneous.

In an SI (Spark Ignition) Engine, an air-gasoline mixture is injected into a cylinder where it is compressed and then ignited by an electrical spark .

Answer 2

The diesel engine is a type of internal combustion engine. It is a compression ignition engine, in which the fuel ignites as it is injected into the engine. By contrast, in the gasoline engine the fuel is mixed first and then ignited by a spark plug. Also, diesels generally have high compression ratios, to enable compression ignition, whereas in gasoline-burning engines, compression ignition is undesirable.

The engine operates using the diesel cycle.

The term spark-ignition is normally used to refer to internal combustion engines where the fuel-air mixture is ignited with a spark. The term contrasts with compression-ignition engines, where the heat from compression alone ignites the mixture. Spark-ignition engines can be either two-stroke or four-stroke, and are commonly referred to as "gasoline engines" in US English and "petrol engines" in British English. However, these terms are not preferred, since spark-ignition engines can (and increasingly are) run on fuels other than gasoline, such as autogas (LPG), methanol, ethanol, compressed natural gas (CNG), hydrogen, and (in drag racing) nitromethane. A four-stroke spark-ignition engine is an Otto cycle engine.