Powertrain Overview: Liquid Petroleum Gas (LPG)

Since the creation of the first modern automobile nearly a century and a half ago, there has been one dominant engine option on the market, the gasoline internal combustion engine. Now the gasoline internal combustion engine has some challengers trying to steal the crown. There have been many different types of engines in the past but many of them relied solely on fossil fuels to operate.

Recently though, because of increasing fuel economy standards and emission awareness, a new breed of engines is emerging, many relying on electricity to aid in powering the vehicle. With these new power plants comes a new set of rules and warnings on how to repair them. A lot of collision technicians have an idea about how some of the new powertrains work, but not a full understanding of what is going on under the hood. It is important to understand the inner workings of the engine in order to safely and properly diagnose and repair them after a collision. In this series, we’ll walk you through many of the current engine options and how they convert the fuel they’re consuming into usable power. Let’s explore the liquid petroleum gas, or LPG (also known as propane) internal combustion powertrain.

A LPG powertrain is nearly identical to a traditional gasoline or CNG internal combustion engine. There are a few differences though. The tanks that fuel is stored in is different, because the fuel is in a liquid state, it is stored at lower pressures than CNG but higher pressure than gasoline. Although LPG is in liquid form, it will instantly turn into a gas if it is allowed to expand. Also, when the gas vaporizes it has a cooling effect. This can be beneficial to cause the same cooling affect as a turbo or supercharged powertrain. The gas is under higher pressure when it leaves the tank so it must pass through a pressure regulator to lower the pressure before it can be burned.

LPG engines have a significant amount of sensitive electrical components on them. These powertrains use a 12-volt battery system to start the vehicle and power the accessories. The battery is charged by an alternator powered by the engine. Because of this, it is crucial to disconnect and isolate the battery and electrical system when making repairs and welding on the vehicle. The added electrical current from welding can damage important electrical components for the engine. The high-pressure gas tanks and lines will require special care when servicing. There will normally be pressure releases built into tanks that may need inspection after collisions. Also note, LPG is very sensitive to temperature change. For this reason, storage tanks should only be painted a light or reflective color. Dark colors absorb heat and can cause the relief valve to open and vent the gas.

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