There are a number of different metrics that can be used to measure the performance of an engine. These include torque, brake horsepower (or Pferdestärke, also known as PS), and fuel consumption. However, one of the most important metrics is thermal efficiency, which is typically expressed as brake thermal efficiency (BTE). But what is it, and why does this efficiency measure matter? We explore some of these questions below.
Brake thermal efficiency or BTE, is used to describe the proportion of chemical energy released during engine fuel combustion that is converted into useful mechanical power at the engine’s output shaft, compared to the energy lost as heat or other non-productive outputs. Or in other words, brake thermal efficiency describes how much of a car's fuel is turned into energy that powers the vehicle and how much is lost as heat.
A high brake thermal efficiency means that a vehicle will be able to drive further or operate for longer on one single fuel tank.
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Brake thermal efficiency is important, as the value of this metric has major implications for cost, environmental impact, and engine capacity.
By having a high BTE, this means that a car is able to get more miles out of every liter of fuel in its tank. So, while an engine that has a low BTE might allow a vehicle to drive 400 miles on a full tank, a high brake thermal efficiency might get you to 600 or 700 miles with the same amount of fuel.
This also has price implications. With improved efficiency, car owners are able to get more value out of every tank of fuel. Rather than having to pay for a new tank of gas every 10 journeys, it might now be 15. This means the car owner pays less for the miles they drive.
The other key benefit is environmental. Burning fuel releases emissions. For every liter of fuel burnt, there is an equivalent release of CO2 and other emissions. However, as with price and range, with an improved brake thermal efficiency, an engine is able to power a vehicle and produce fewer emissions for the same amount of vehicle usage.
The implications of this are significant. In fact, when these efficiency savings are applied across the full global vehicle parc and the full operational life of a vehicle, this equates to a significant possible global emissions saving.
For hybrids in particular, thermal improvements make this technology a highly valuable and more economic option, making hybrids a relevant alternative to BEVs. You can learn more about hybrid technology and its use cases in our articles on HEVs, PHEVs, and REEVs.
Thermal efficiency can provide economic and environmental benefits for both consumers and companies
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Given the benefits of a high BTE, it is helpful to understand how this metric is quantified and what a ‘good’ rating looks like.
Assessing the thermal efficiency of an engine requires rigorous testing. This involves quantifying the brake power of the vehicle and measuring it against the rate of energy supplied by the fuel.
Historically, brake thermal efficiency levels have hovered somewhere between 35% and 38%. However, as improvements continue to be made, we could yet see engines that reach over 45% BTE. At Horse Powertrain, we have already made significant strides, with some of our latest engines reaching brake thermal efficiency levels of 44% and beyond.
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As the automotive industry adapts to new regulations and a changing market, where environmental and economic factors play an increasingly significant role, the importance of efficiency improvements, such as those measured by brake thermal efficiency, will only continue to grow.
At Horse Powertrain, we have made it our mission to develop the combustion and hybrid engines of the future, ensuring that the cars on the road 50 years from now are as clean and efficient as possible.
To find out more, view our selection of combustion and hybrid powertrain solutions here.