* Hydrocarbons (HC): SI engines emit more HC than CI engines because the fuel is not completely burned during the combustion process. This is due to the lower compression ratio and the fact that the fuel is mixed with air before it is ignited.
* Carbon monoxide (CO): SI engines emit more CO than CI engines because the fuel is not completely burned. CO is a product of incomplete combustion.
* Nitrogen oxides (NOx): SI engines emit less NOx than CI engines because the combustion temperature is lower. NOx is formed when nitrogen and oxygen in the air react at high temperatures.
* Particulate matter (PM): SI engines emit less PM than CI engines because the fuel is burned more completely. PM is made up of tiny particles of soot and other pollutants.
Compression Ignition (CI) Engines
* HC: CI engines emit less HC than SI engines because the fuel is more completely burned during the combustion process. This is due to the higher compression ratio and the fact that the fuel is injected directly into the cylinder.
* CO: CI engines emit less CO than SI engines because the fuel is more completely burned.
* NOx: CI engines emit more NOx than SI engines because the combustion temperature is higher.
* PM: CI engines emit more PM than SI engines because the fuel is not burned as completely.
In general, CI engines are more efficient than SI engines, but they also emit more pollutants. This is why emissions regulations are becoming increasingly strict for CI engines.
