Combined Heat and Power Focus

DECC's Free resource supporting the development of CHP

CHP Helpline 0845 365 5153 or 01235 753033

Compression-ignition Engines

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


 NOx (g/kWh)

CO2 (g/kWh)

SO2 (g/kWh) 

 Firing on natural gas (with pilot oil)




 Firing on heavy fuel oil





Other topics


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What's New

UK CHP Development Map

UK CHP Development Map

UK CHP Development Map

UK CHP Development Map Screenshot

The UK CHP Development Tool is the latest version of the map, originally developed as a tool aimed at assisting power station developers consider the opportunities for supplying heat and development of combined heat and power (CHP) as required under planning policy. However, it can also be used by both small and large organisations to help identify the locations where the supply of CHP heat would have the greatest potential, and therefore the largest positive environmental impact.

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