LPG Car & LPG Gas Auto Conversion – How an LPG Gas Car Works
LPG gas auto conversion to an LPG car is when a second fuel system is added to a vehicle to use LP gas for cars in an internal combustion engine. The LPG car user can then choose between using either fuel. LPG gas for cars is added to save money on fuel costs. Gas for cars can be propane, butane or a mixture of the gases.
When LPG – liquefied petroleum gas – is used in LP gas cars with internal combustion engines or for stationary engines, like generators, it is called Autogas (LPG gas for cars).
LP gas for cars is a varying mixture of propane and butane.
How gas for cars works in an engine is fundamentally the same as a gasoline (petrol) powered internal combustion engine.
The engine block, pistons, spark plugs, ignition system, lubrication system and electricals all work the same on LPG fuel, consisting of propane, butane or a blend of the two and are also referred to as natural gas liquids – NGL.
The two main differences in how LP gas for cars works in an LPG gas auto are the fuel itself and the fuel storage and intake systems.
With an octane rating of over 100, LPG works with virtually any petrol engine.
There are 25 million LP gas cars & LPG vehicles worldwide.
An LPG car can be OEM single fuel models or dual fuel LPG vehicle conversions that run on either LPG – also known as Autogas – or petrol.
LPG Fuel – What is Autogas (LPG Gas for Cars)
LPG is a fuel gas. LPG – Liquefied Petroleum Gas – is commonly called Autogas (LP gas for cars) when used as fuel for an LPG automobile with internal combustion engines. LPG gas for cars is either propane or a propane and butane mix.
It can also be used for fixed ICE installations, like generators.
Liquefied petroleum gas or liquid petroleum gas – LPG – also identified as propane or butane, are flammable hydrocarbon gas mixtures used as fuel in vehicles, as Autogas, as well as for home heating and cooking fuel.
LPG Conversion for an LPG Gas Car
There are four main types of LPG conversion systems for an LPG gas car including LPG Liquid Phase Direct Injection (LPDI), Liquid Phase Injection (LPI), Vapour Phase Injection (VPI), and Converter-and-Mixer Systems.
The newest LPG conversion system for an LPG gas auto – LPDI – is also the most advanced whilst the oldest converter-mixer LPG gas systems are, by far, the least sophisticated LPG conversions.
LPG Car Conversion Systems in Summary
Here are the four LPG car conversion systems for an LPG gas auto from newest to oldest…
- LPG Liquid Phase Direct Injection (LPDI) has liquid LPG injected directly into the combustion chamber. LPDI is the most advanced LPG gas car system.
- LPG Liquid Phase Injection (LPI) systems inject liquid directly into the intake manifold.
- LPG Vapour Phase Injection (VPI) the gas exits the converter under pressure and is injected into the intake manifold.
- LPG Converter-and-Mixer Systems is the oldest style LPG system. Liquid fuel converts into vapour and is then mixed with air before going into the intake manifold.
LP Gas Car – How an LPG Gas Auto Works
Autogas is another name for LPG gas for cars when used as fuel in internal combustion engines.
It is typically a mixture of propane and/or butane, which can also be sued for fixed applications, like generators.
An LPG car uses LPG instead of petrol (gasoline) or diesel. An LPG gas auto can be an LPG automobile straight from the factory, or they can be LPG car conversions.
LPG can fuel various LPG vehicles, including light commercial LPG vehicles, as well as LPG cars.
In different countries, the LPG supplied can be propane, butane or propane-butane blends.
What Does LPG Conversion Do to an Engine
Regarding LPG conversion and LPG vs petrol engine life, is LPG good for an LPG automobile and does LPG damage engines:
- LPG gas for cars prevents pre-ignition (knocking) in an engine, as it is over 100 octane
- Manufacturers offer dual-fuel models with the same warranties
- An LPG automobile changes the fuel storage and intake systems of the engine. These are the only major differences
- LPG gas car conversions, to engines, do not affect factory warranties
- LPG doesn’t damage engine parts
- LPG vs petrol is cleaner burning than petrol or diesel in an engine
- LPG may actually prolong engine life
What is an LPG Conversion?
An LPG conversion is taking a normal petrol powered vehicle and adding a secondary LPG automobile fuel system.
Almost all vehicles fueled by petrol are convertible to LPG vehicle operation at a reasonable cost.
These dual-fuel LPG car systems allow an LPG gas car to operate on either LPG or petrol.
The petrol tank still remains in the LPG gas auto.
The driver can switch from gas to petrol or vice-versa.
The driver is typically provided with a switch and can select which fuel they choose to use.
Having two fuel tanks can double an LPG vehicle’s range.
With both the petrol and LPG tanks filled, a dual fuel LPG gas auto cruising ranges of 1000km or more are not unusual.
Advantages of LPG – What Does LPG Do to an Engine – How Does LPG Work
What LPG does to an engine is beneficial and how does an LPG gas car work.
Autogas (gas for cars) engines have lower running costs.
LPG is typically less expensive than petrol or diesel.
Engine oil and spark plugs need changing less often with an LPG gas auto, for reduced service costs.
Environmental benefits of LPG vehicles include reduced particulate, CO2 and NOx emissions.
Octane ratings over 100 allows for higher compression ratios, which can increase power output.
Different Autogas Fuel Tanks
Did you know that many new petrol cars come with plastic or composite fuel tanks?
Autogas tanks for LPG cars are typically made from welded heavy gauge steel.
The image shown is a toroidal LPG fuel tank in the spare tyre well.
The steel is generally 3mm to 6mm thick, depending on the tank design.
An LPG gas auto tank design withstands many times its maximum operating pressure.
They are much more puncture resistant and will survive much greater impacts than a typical petrol or diesel tank.
The tank mounting systems are also designed to ensure that the tank will not become dislodged, even in a 20 G impact.
Modern LPG gas car tanks are compact space saving designs.
The new toroidal LPG tanks are donut shaped and fitted within the spare wheel well.
The spare is replaced by a small emergency inflation kit.
Four Types of Autogas Conversion Systems Explained
There are four types of Autogas (gas for cars) fuel intake systems.
Let’s have a look at them from oldest to newest technology:
1. LPG Converter-and-Mixer Systems
Converter-and-mixer systems are the oldest style, dating back decades and still widely used.
The liquid fuel converts into vapour and is then mixed with air before going into the intake manifold.
2. LPG Vapour Phase Injection (VPI)
Vapour phase injection (VPI) systems use a converter-and-mixer system.
The gas exits the converter under pressure and is injected into the intake manifold.
Electrically controlled injectors improve the metering of fuel to the engine, fuel economy and power, and reduce emissions.
This has been the most popular type of LPG vehicle system in recent years.
3. LPG Liquid Phase Injection (LPI)
Liquid phase injection (LPI) systems inject liquid directly into the intake manifold.
That is where it vaporises, not using a converter.
The system works by pumping LPG at high pressure from the LPG gas auto tank to the engine inlet manifold via a set of liquid LPG injectors.
The injectors spray the liquid LPG into the intake manifold.
The fuel vaporising in the intake manifold cools and increases the density of the intake air.
This substantially increases power output, improves fuel economy and has lower emission, when compared to VPI systems.
4. LPG Liquid Phase Direct Injection (LPDI)
Liquid phase direct injection (LPDI) are the most advanced systems.
Liquid LPG is injected directly into the combustion chamber.
The LPG instantly vaporises, cooling the combustion chamber fuel-air mixture during the compression stroke.
This provides further performance and emission improvements.
This cooling effect increases the density of the air-fuel mixture.
So, power and torque are maintained with fewer CO2 emissions.
The effect is like intercooling on turbocharged cars.
An Electronic Control Unit (ECU) controls the various components of the liquid injection system, including the injectors.
LPG injection signal optimises the flow and LPG injection timing.
The ECU is calibrated to the specific vehicle and engine.
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Eric Hahn has over a decade of experience in the LPG industry and has become a key figure in shaping how LPG is marketed and communicated. As the creator of one of the world’s first LPG blogs, Eric has authored over 200 technical posts, helping educate and inform the industry and consumers.
Eric has served on multiple committees for Gas Energy Australia and the World LPG Association (WLPGA), contributing to important discussions and advancements within the global LPG sector. He has presented at WLPGA Annual Conferences, sharing his expertise as a speaker, panellist, and panel chair.
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Steve Reynolds
Technical Consultant
Steve Reynolds is a leading expert in the LPG industry with over 22 years of experience. As part of the national management team at ELGAS, Steve ensures the safe and efficient storage, handling, and transportation of LPG. He serves as the lead investigator for incidents and collaborates with authorities on industry developments.
Steve is a technical advisor to Standards Australia and Gas Energy Australia (GEA), and an active member of the World LPG Association (WLPGA), contributing to global standards and technical reviews. He holds a BSc. (Hons) in Industrial Chemistry from UNSW and has held senior safety and technical roles at ELGAS, making him a trusted authority in LPG safety and standards.