Combustion
Fuel and air are mixed and burned within the combustion chamber to convert chemical energy of the fuel into thermal energy within the gas-stream prior to entry into the turbines.
The needs of the system depend greatly on the application ie. civil aerospace, military aerospace, marine or power generation. However there are many common themes of technology that span all sectors.
The key discriminating technology of combustion is the generation and control of pollutant emissions -in particular NOx, particulate matter, unburned hydrocarbons and carbon monoxide. For each product, these are closely regulated and monitored. Rolls-Royce has a clearly laid- out, long term strategy and commitment to control gaseous emissions.
Emissions & pollutant reduction
The requirements in the defence sector are complementary to other business sectors but also have unique elements of their own. The design of the main combustion system is driven far more by constraints of weight and excursions to extremely high fuel:air ratio, which can have implications for stealth. The reheat system or afterburner also requires distinctive technology, being the only application in the Rolls-Royce businesses where low pressure combustion is required in vitiated (oxygen reduced) air.
Combustion for defence engines
The temperatures within the combustion chamber are the hottest in the engine - fuel is burned in the combustion chamber at temperatures of over 2000°C yet they are still expected to last the many hours of operation between overhauls. This requires substantial technology in the form of wall materials (both metallic and ceramic), coatings and manufacturing technology.
High pressure/Hot end technologies
Rolls-Royce engines operate with a wide range of fuels in all sectors. This is most apparent in the energy business where a wide range of gaseous fuels may be employed, often with the need for a “fall back” liquid fuel if the main fuel supply is cut off.
There is increasing interest and activity in all sectors in the development of alternative fuels – either fossil fuel-based, or based on renewable sources and sustainable sources not conflicting with food and water. This requires additional combustion research to understand the impact on combustion performance and, in the extreme, a redesign of the combustion system.
