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Difference Between CNG and LPG

Difference Between LPG and CNG - Definitions, Advantages, Disadvantages, Practice Problems & FAQs

Since we were little children, we have heard from our parents that gas cylinders used in kitchens are filled with LPG. Compared to the previously utilised kerosene stove or coal-burning in "Chulha," both produce a lot of smoke. LPG is the cleanest and most efficient fuel we use for cooking purposes.

Most recently, we learnt that all gasoline and diesel-powered automobiles would be replaced with clean fuel vehicles.

CNG is the name for this "clean fuel gas." Low hydrocarbon emissions and ozone-producing-free vapours are produced by it. To combat the rising levels of air pollution CNG was the solution as this fuel produces gases which are not harmful to humans, animals and the environment. The most frequent queries are, "What are CNG and LPG," and "How are they different from one another?"

Table of Contents

  • CNG
  • LPG
  • Difference between LPG & CNG
  • Advantages of CNG & LPG
  • Disadvantages of CNG & LPG
  • Practice Problems
  • Frequently Asked Questions - FAQs


The term"CNG" refers to “compressed natural gas”, which is essentially pure methane gas (CH4) that is used to produce a clean fuel that is pollutant-free when burned. CNG is frequently referred to as "clean fuel”. Natural gas is primarily made up of methane (CH4), which is compressed to less than 1% of its volume at typical atmospheric pressure to create compressed natural gas or CNG. CNG gas is in rigid containers at a pressure of 20–25MPa. CNG is significantly less expensive than premium gasoline, which encourages car owners to switch from gasoline or diesel to this cleaner fuel.


The term"LPG" refers to “liquefied petroleum gas” which is a mixture of light gaseous hydrocarbons like propane, butane, and other light petroleum products that have been filled in the storage tanks under extremely high pressure and turned into a liquid. Pressurised cylinders are filled with LPG before being transported or stored. In order to identify any leakage from these pressured cylinders promptly, a little amount of the foul-smelling chemical ethyl mercaptan is added to these pressurised cylinders.

Difference between LPG & CNG

DIfferentiating Factor CNG LPG
Application CNG is used as a fuel in vehicles, for the generation of electricity and used for cooking as well. It can be used for many things, including cooking and heating the dwellings. LPG is also used in agriculture and various industry as well.
Component Methane serves as the main ingredient in CNG. Propane and butane make up the majority of LPG.
Environmental factor It generates comparatively fewer greenhouse gases (in comparison with LPG). It generates a substantial amount of greenhouse gas like carbon dioxide.
Safety measure Given how quickly it disperses into the air, it is generally safe.

Due to the fact that it has a low ignition temperature (The temperature at which a substance first ignites is known as the ignition temperature), it is very combustible.

Sources Oil wells, bed methane wells, coal wells, and even natural gas wells are the main sources of CNG. LPG is primarily produced during the extraction of natural gas and crude oil from the reservoirs.
Calorific value The calorific value of CNG is 35 to 40MJ/m3. Compared to CNG, LPG has a higher calorific value of 90 to 95MJ/m3. Therefore, compared to biogas, gasoline, diesel, kerosene, and CNG, LPG is a more effective fuel.
Cost CNG is cost-effective fuel if compared with LPG. LPG is not cost-effective fuel if compared with CNG.

Advantages of CNG & LPG

  • CNG-powered vehicles are safer and more effective than gasoline-powered ones. The least expensive, cleanest fuel with the lowest environmental impact is CNG. Since CNG is lighter than air, it disperses through the air more quickly and evenly.
  • Both CNG and LPG are clean-burning fuels with minimal residue. Therefore, as less residue is deposited on the equipment of the machines and vehicles, the cost of maintaining the machines and vehicles goes down. Hence, the lifespan of the machines and vehicles increases.
  • When burned, they produce a good amount of heat energy.

Disadvantages of CNG & LPG

  • Due to the presence of methane in CNG and propane+butane in LPG, which burns easily in the air and has a low ignition temperature, both CNG and LPG run the risk of catching fire when the cylinder's nozzle is left open or in the event of any form of leak.
  • In comparison to liquid fuels, the storage area needed for the cylinders containing CNG or LPG is greater. In comparison to liquid fuels like gasoline and diesel, both gases are consumed more. Moreover, additional vehicle modifications are needed in order to install CNG cylinders in the vehicles.
  • Prior to the introduction of CNG, LPG was considered the only clean fuel. Although CNG has gained acceptance as a clean fuel, its volatility has prevented it from being used as a cooking gas. Also, due to its high auto-ignition temperature (540 °C) and limited flammability range of 5 to 15%, CNG is not used in our households for cooking purposes.
  • LPG continues to be a distinctive commodity for cooking and household lighting. Nowadays, LPG pipelines are installed in the majority of homes since they make it easy and safe to carry liquid petroleum products. As a result, even though both CNG and LPG have a few inherent limitations, they are both very valuable fuels.

Practice Problems

Q.1 What is the calorific value of CNG?

  1. 35 to 40MJ/m3
  2. 350 to 400MJ/m3
  3. 60 to 80MJ/m3
  4. 65 to 70MJ/m3

Answer: (A)

Solution:The calorific value of CNG is 35 to 40MJ/m3. So, the correct answer is option (A).

Q.2 Pick the odd one out.

  1. LPG
  2. Petrol
  3. Diesel
  4. Kerosene

Answer: (A)

Solution:Liquid fuels include kerosene, diesel, and petrol. LPG is a fuel which is in gas form when used. Therefore, "LPG" is the right response. So, the correct answer is option (A).

Q3. Any substance that undergoes combustion is called:

  1. Fuel
  2. Combustible substance
  3. both a and b
  4. none of these

Answer: (C)

Solution:A substance is said to be combustible if it can burn in the presence of air. Fuel is a combustible substance which produces useful energy when undergoes combustion. There is a chemical change during combustion. Heat is produced when the substance reacts with oxygen. So, the correct answer is option (C).

Q.4 Which of the following is not true for LPG?

  1. LPG is not cost-effective fuel if compared to CNG.
  2. The calorific value of LPG is 35 to 40MJ/m3.
  3. Propane and butane are the constituent gases in LPG.
  4. LPG is primarily produced during the extraction of natural gas.

Answer: (B)

Solution:Compared to CNG, LPG has a higher calorific value of 90 to 95MJ/m3. 35 to 40MJ/m3 is the calorific value of CNG. Hence, option (B) is the correct choice.

Frequently Asked Questions - FAQs

Q1. Can LPG gas is a substitute for CNG in our vehicles?

Answer:Both CNG and LPG are in the gaseous state. But the gases are not the same. So both LPG and CNG have different physical and chemical properties and engines in the vehicles are modified according to the type of fuel (gas) to be used. Hence, LPG can’t be substituted for CNG or vice versa in our vehicles.

Q2. LPG or CNG, which is safer?

Answer:LPG is heavier than air, whereas CNG is lighter. Therefore, in the event of a leak, CNG spreads quickly through the air, whereas LPG remains in the lower part of the area of leakage. Because LPG does not diffuse in the atmosphere as CNG does, it poses a greater risk of spillage than CNG. Hence, CNG is a safer option than LPG.

Q3. Which is superior, CNG or gasoline?

Answer:CNG vehicles emit fewer greenhouse gases. Cars powered by gasoline emit toxic gases. CNG vehicles have less power than gasoline vehicles. CNG vehicles have less power than gasoline vehicles. Hence, CNG cars are more eco-friendly and gasoline cars provide better power to vehicles.

Q4. What does CNG's future hold?

Answer:There has been an increase in the use of CNG vehicles in India along with the rise in fuel prices. However, CNG vehicles are a good choice of fuel types when it comes to adhering to eco-friendly measures in addition to lowering prices.

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