Final answer:
In turbine engines, approximately 20% to 25% of the incoming air is used for combustion, with an air to fuel ratio typically between 15:1 and 50:1. Efficiency of an engine is determined by the ratio of work output to heat input. For a 42.0% efficient engine, 58% of the heat is lost to the environment.
Step-by-step explanation:
In a turbine engine, such as those used in jet aircraft, a significant portion of the air passing through is not used for combustion. Roughly 75% to 80% of the air is bypassed around the core of the engine for cooling and to provide mass flow through the engine. This means that only about 20% to 25% of the air is involved in the combustion process where it is mixed with fuel to produce thrust.
The air to fuel ratio in modern jet engines typically ranges from about 15:1 to 50:1, depending on the type of engine and the operating conditions. For example, during takeoff, a lower air to fuel ratio is used for a higher thrust, whereas during cruise a higher air to fuel ratio is used for better efficiency. At optimal cruising, the ratio could be as high as 50 parts air to 1 part fuel.
When assessing the efficiency of an engine, one often looks at the thermodynamic efficiency, which is the ratio of work output to heat input. If an engine has an efficiency of 42.0%, the work done is 42.0% of the heat absorbed from the fuel's combustion. Consequently, the ratio of heat transfer to the environment to work output is 58.0%, as the remaining heat is not converted into work. Calculating efficiency and understanding waste heat are crucial in this context.