"Combustion efficiency" refers to how effectively fuel is burned or converted into heat energy in a combustion system. The higher the combustion efficiency, the more efficient the process of burning fuel and producing usable energy. Full definition
This 12 Valve mode results in swirl of the intake charge which increases combustion efficiency, resulting in improved low end torque and better fuel economy. (en.m.wikipedia.org)
Four valves per cylinder and advanced combustion chamber shapes contribute to high combustion efficiency with low combustion noise, alongside very low mechanical noise levels. (sybarites.com)
With this knowledge, researchers can develop better climate models and improve fuel combustion efficiency. (scientificamerican.com)