What is Combustion Efficiency?

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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 15 October 2019
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Combustion efficiency is a measure of how efficiently a device consumes fuel. Ideally, it would be measured at 100%, meaning that the fuel was completely consumed. In practice, this level of efficiency is impossible to achieve, but it's possible to come close. The lower the combustion efficiency, the less efficient the device is, making it expensive to run, wasteful of fuel, and harmful for the environment.

Several parameters are considered when measuring combustion efficiency. One is the composition of the fuel, for the purpose of determining how much potential energy is present. Another is the amount of oxygen entering the device, with higher oxygen levels tending to promote more complete combustion. The temperature and composition of the gases being vented from the device is also important; certain types of flue gases indicate that combustion is not complete, and high temperatures indicate that heat is being wasted by being vented off instead of utilized.

One of the classic examples of combustion inefficiency is a woodburning fireplace, which often has an efficiency rate of less than 10%. This means that the fireplace is not fully utilizing the energy in the wood, generating lots of byproducts of incomplete combustion like soot and harmful gases, and losing heat up the chimney rather than heating a room. Conversely, specialized types of gas heaters can have efficiency rates of over 90% when they are operating properly.


Combustion efficiency is an important concern for a number of reasons. For people paying to fuel devices which burn fuel for energy or heat, the more efficiently a device uses fuel, the less it costs to run, which is good. For people concerned about the environment, more efficient combustion is beneficial because it reduces pollution; this also reduces wear and tear on equipment caused by accumulation of particulates and harmful flue gases.

Ideally, combustion efficiency would reach a stoichiometric stage, a perfectly balanced reaction which consumes 100% of the fuel. This would require highly controlled conditions which are simply not available in the real world. However, it is possible to monitor a device to determine its efficiency during different operating periods, for the purpose of making adjustments which can increase efficiency. This monitoring can be critical on the industrial level, when fuel waste can become quite costly, but people can also benefit from monitoring combustion efficiency in their own homes, as they can save on fuel costs substantially just by making sure that devices are efficient.


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Post 3

@NathanG - There are some techniques that you can use to improve internal combustion engine efficiency. One of the easiest is to use the correct viscosity for your oil. Oil acts as a lubricant to enable your engine to move about freely as it does its work.

The correct viscosity will make your engine more efficient, improving your miles per gallon and generating less heat. I always pick the highest quality oil for my engine, even if I have to pay a little more, because it results in better performance and that puts money in my pocket in the long haul.

Post 2

@NathanG - Yes, diesel engines are more efficient than gas engines. However, they have a number of disadvantages working against them. They are heavier and more expensive than gas engines, and they can vibrate, make smoke and be a little more difficult to start in the winter time. There are other disadvantages that work against them and overall make them impractical for the mass consumer market.

My brother’s nephew works in the trucking industry, and of course most trucks use diesel engines, where the improved fuel efficiency is very important given the cargo demands, while the disadvantages are rather unimportant.

We’re all used to hearing rattling, noisy and sometimes fuming trucks on the road, and have learned to just stay out of the way.

Post 1

When gas prices go up people invariably want cars with improved engine efficiency. That’s why the first two cars that I owned were Hondas. I was easily getting 35 plus miles to gallon, although I realize now with some of these hybrid cars they can top that easily.

My Honda would just go and go before it came time to fill up. I think besides hybrids and smaller cars the only other vehicles with improved combustion engine efficiency would be those using diesel engines.

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