Compression-ignition engines generally operate with lower air-to-fuel ratios and higher combustion temperatures than gas turbines. The aim is to maximise efficiency but the result in environmental terms is to give relatively high NOX emissions levels per unit of power generated. Actual NOX emissions vary widely between different engine designs: in some cases, it is possible to reduce NOX emissions by operating at a lower engine efficiency, albeit with a small increase in CO2 emissions.
Compression-ignition engines can operate on gas fuels if a small quantity of ‘pilot oil’ is injected to ignite the gas. This fuel option gives lower NOX emissions than fuel oil but usually reduces the power output of the engine.
|Emissions from compression-ignition engines|
Firing on natural gas (with pilot oil)
Firing on heavy fuel oil
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