LPG (Liquefied Petroleum Gas) and CNG (Compressed Natural Gas) are both alternative fuels used to power vehicles and for various industrial/commercial applications. While they share some similarities as cleaner-burning alternatives to petrol or diesel, they differ significantly in composition, properties, and uses. Here’s a detailed breakdown:
What is LPG?
LPG is a flammable hydrocarbon gas mixture derived from two primary sources:
Natural gas processing: Separated from raw natural gas during extraction.
Crude oil refining: Produced as a byproduct when crude oil is refined into petrol or diesel.
Composition
LPG is primarily composed of:
Propane (C₃H₈)
Butane (C₄H₁₀)
It may also contain small amounts of other hydrocarbons, but propane and butane are the main components. The ratio of propane to butane can vary by region and season (e.g., more propane in colder climates for better vaporization).
Key Properties
Liquefaction: LPG is stored and transported as a liquid by applying moderate pressure (typically 7–10 bar) at room temperature, which reduces its volume by ~270 times—making it highly portable.
Energy density: Higher than CNG but lower than petrol/diesel. It releases ~25–30% less energy per liter than petrol but is often cheaper per unit.
Combustion: Burns cleanly, emitting fewer pollutants (e.g., CO₂, nitrogen oxides, particulates) than petrol or diesel.
Common Uses
Vehicle fuel (dual-fuel systems allow switching between LPG and petrol/diesel).
Domestic heating, cooking, and hot water.
Industrial applications (e.g., forklifts, generators).
What is CNG?
CNG is methane-rich gas derived from natural gas reserves. It is primarily composed of methane (CH₄), with small amounts of ethane, propane, or nitrogen.
Composition
Methane (CH₄): 90–95% of the mixture.
Trace gases: Ethane (C₂H₆), propane (C₃H₈), and nitrogen (N₂).
Key Properties
Compression: CNG is stored as a gas under high pressure (200–250 bar) to reduce its volume (by ~200–250 times), allowing it to be stored in cylindrical tanks.
Energy density: Lower than LPG, petrol, and diesel. It provides fewer kilometers per unit volume, meaning larger storage tanks are needed for equivalent range.
Combustion: Extremely clean-burning, with the lowest CO₂ emissions among fossil fuels. It emits almost no particulates or sulfur oxides.
Common Uses
Vehicle fuel (especially in public transport, taxis, and commercial fleets).
Industrial and residential heating (less common than LPG in households).
Power generation (as a cleaner alternative to coal or oil).
