# Heat of Combustion Calculator

Created by Rahul Dhari
Reviewed by Steven Wooding
Last updated: Dec 01, 2021

This heat of combustion calculator will tell you the heat released during the combustion process. When fuel burns or undergoes the combustion process, it combines with oxygen in the air and forms carbon dioxide and water vapor along with some heat. The heat of combustion, also known as the higher heating value, is a function of the number of moles of water vapor formed and considering the heat of vaporization.

The heat of combustion is a crucial parameter in the area of energy and heat used to drive machines like internal combustion engines, fuel cells, waste heat recovery to reuse it. It is also used to estimate the quality of fuels like natural gas or coal. Read on to understand if you are wondering what higher heating value is or how to calculate the heat of combustion?

## What is heat of combustion?

Definition of the heat of combustion is the amount of energy released when a particular fuel undergoes combustion. The heat of combustion goes by several names like higher heating value, higher calorific value, and upper heating value. When fuel is combusted, one of the byproducts is water vapor that is formed due to heat of vaporization and is often wasted when allowed to escape. However, in the formula for the heat of combustion, the energy to form water vapor is considered. The heat of combustion having a symbol, $H_c$ is given by the equation:

$\quad H_c = LHV + H_v \ \frac{n_{H_2O}}{n_{fuel}}$

where:

• $LHV$Lower heating value;
• $H_v$Heat of vaporization;
• $n_{H_2O}$Number of moles of water $(\text{H}_2\text{O})$ released; and
• $n_{fuel}$Number of moles of fuel combusted.

Heat of vaporization definition: the amount of energy required to transform the liquid into gas form.

The lower heating value is the energy produced from the combustion of fuel, considering water vapor loss. In other words, lower heating value is the difference between higher heating value and heat of vaporization of water vapor. The heat of combustion, lower heating value, and heat of vaporization are measured in the units of energy per mass, i.e., kJ/kg or BTU/lb.

## How to calculate heat of combustion?

Now let's have a look at the steps for calculating the higher heating value:

1. Enter the lower heating value of the fuel.
2. Insert the heat of vaporization of water of the fuel.
3. Fill in the number of moles of water vaporized.
4. Enter the number of moles of fuel combusted.
5. The calculator uses the heat of the combustion equation to return its value.

💡 If the lower heating value is unknown, you can select the fuel from the list to use directly. The list contains the lower heating value of natural gas and other common fuels.

## Example: Using the heat of combustion calculator

Determine the heat of combustion of methane given its lower heating value is 50 MJ/kg and it releases 5 moles of water vapor when 2 moles of fuel is combusted.

1. Select Methane from the list of fuels.
2. The heat of vaporization for water as 2.257 MJ/kg.
3. Fill in the number of moles of water vaporized as 5.
4. Enter the number of moles of fuel combusted as 2.
5. Using the heat of combustion formula:
$\qquad \scriptsize {H_c} = 50 + 2.257 \frac{5}{2} = 55.64 \text{ MJ/kg}$

💡 You can repeat the same process to calculate the heat of combustion for ethanol.

## FAQ

### What is the heat of vaporization?

The heat required to add to a liquid for converting it to a gaseous form is the heat of vaporization. It is measured in the units as J/mol or kJ/kg and BTU/lb.

### What is the heat of vaporization of water?

The heat of vaporization of water is 2.257 MJ/kg or 44.02 kJ/mol.

### How do you find the heat of combustion?

For the calculation of heat of combustion:

1. Divide the number of moles of water vaporized by number of moles of fuel combusted.
2. Find the product of heat of vaporization of water and the ratio of moles.
3. Add the resultant to lower heating value of the fuel to obtain heat of combustion.

### What is lower heating value?

The lower heating value is defined as the energy produced combusting a fuel, considering the loss of water vapor. It is measured in the units of energy per mass or kJ/kg.

Rahul Dhari
Select a fuel to see its lower heating value to begin.
Fuel
Select...
Lower heating value
BTU/lb
Heat of vaporization of water
BTU/lb
Number of moles
Number of moles of water vaporized
mol
Number of moles of fuel combusted
mol
Combustion
Heat of combustion
BTU/lb
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