With petrol prices increasing ever so often, it makes sense to convert your petrol car to a bi-fuel one that runs on either petrol or LPG. This CarToq guide to LPG kits for cars will help you choose the best kind of LPG kit for your car and understand how the system works.
LPG kits can cost from about Rs. 25,000 for a basic kit up to Rs. 45,000 for a high-quality kit that is suitable for most modern cars. Some of the big brands of LPG kits that are available in India include Lovato Autogas, BRC, StarGas, Tartirini, OMVL and Zavoli. LandiRenzo, the company that owns Lovato and BRC brands, has set up shop in India recently and will supply aftermarket kits and components for almost all Indian car brands.
There are two kinds of kits available. One is the simple venturi mixer kit that was used with earlier carbureted cars and the second is the sequential kit that is used for modern multi-point fuel injected cars. This guide is for the latter as it is more suited to modern cars.
So what comprises an LPG Kit for your car?
The most critical aspect of an LPG conversion is choosing the size of tank that will fit in your boot. Remember LPG is a heavy gas, and in case of leakage it will settle around the vehicle increasing risk of a fire, and hence it is important to get a proper branded tank that’s securely installed. There are two kinds of tanks available – the cylindrical tank and the toroidal tank. The latter fits in the spare wheel well of the boot of the car, but does not have much capacity. The cylindrical tanks come in 35-litre, 45-litre and 60-litre capacity. The choice of tank will depend on how much space you have in your boot.
At best of times these tanks won’t be able to hold the full amount of LPG (which is a liquid when stored). It can hold only about 85% of the capacity at best, depending on the pressure it is filled at and to maintain a safety margin for expansion.
Most LPG systems usually have the refilling point located close to the storage cylinder, unlike CNG systems that have it in the engine bay mostly. This is a pin type pressure valve that can take an LPG nozzle (similar to what you see on your domestic LPG cylinders, but smaller).
Good LPG kits also come with a pressure gauge that is fitted on the tank, which will tell you the amount of LPG that has been filled in it. Don’t overfill the tank.
The gas pipe is an important component of the kit. It is usually a strong copper tube that transfers gas (in liquid form) from the LPG reservoir to the engine bay. This pipe needs to be strong to prevent leakage, and the installer must take care not to route this pipe close to the exhaust system or around any electrical components that can cause a fire.
The solenoid valve is the next component in the system. This is basically a “tap” that switches on or off the flow of gas from the storage cylinder to the engine. It takes its commands from the changeover switch.
The changeover switch is located in the cabin for the driver to operate. It switches between petrol and gas. When the car is operating on gas alone, this changeover switch will deactivate the petrol fuel pump, shutting off petrol supply to the engine, allowing only gas and vice versa. Changeover switches also act as a gas-fuel gauge by indicating the level of gas in the tank.
Electronic Control Unit (ECU)
The ECU is the brain of the gas-injection system. It piggy-backs with the regular petrol ECU of your car and emulates the signals coming from the petrol ECU to control the gas injectors. It also constantly monitors signals from three sensors to ensure the best operating conditions are maintained. It automatically deactivates the petrol injectors and switches on the gas injectors and vice versa depending on the gas pressure levels.
There are three sensors that come with the kit that tell the ECU what to do with the gas flow. One is the MAP or manifold absolute pressure sensor. It measures the gas pressure in the intake manifold (which supplies the air-fuel mix to the engine). The second sensor senses the gas pressure in the gas injector rail and tells the ECU to regulate gas injection times. The third is the gas-temperature sensor that checks the temperature of the gas, used by the ECU to control gas volume.
Some kits have a fourth sensor which piggybacks on the lambda sensor/oxygen sensor of the vehicle exhaust. It is used to control emissions for the vehicle, but sometimes this can lead to a drop in performance of the vehicle as well (and some installers skip this bit).
Vehicles that don’t use this are often termed as running an “open-loop” system, where there’s no feedback from the exhaust emissions. But if these sensors are connected, it becomes a “closed-loop” system.
Some cars also have an advanced timing sensor fitted to them that alters the ignition timing to run on gas. This gets rid of the power-drop often associated with engines running on LPG, although there’s still some power loss.
Regulator or Vaporizer
If the ECU is the brain of the system, the vaporizer is the heart of the system. It is responsible for converting liquid LPG into gas. It uses heat generated from the engine coolant for this. The regulator is a bulky unit that sends gas to the injectors.
As the name suggests, the gas filter is just a device to filter the gas going to the engine. Sometimes this is replaced by a second safety solenoid to cut off gas flow to the engine in an emergency.
Sequential injector kits come with an injector rail that carries the LPG gas supplied to individual injectors. This is similar to a “common-rail” used in a diesel car.
The gas injectors are connected directly to the engine, near the intake valves. The gas injectors and the petrol fuel injectors are normally located side by side. Some earlier systems don’t have separate gas injectors but directly use the petrol injectors to inject gas as well, by supplying gas directly to the manifold. These systems need more maintenance as petrol injectors tend to get sticky if used only on gas for a long time. It’s recommended to run the car on petrol from time to time.
Always make it a point to get the installation of an LPG kit done by a professional. After the installation is done, get the kit endorsed in the RC book of the car, which will certify it as a dual-fuel car. Most kits these days come with a 1 year warranty on the parts and a number of free services. Check with your installer about this.
Share any experiences of LPG conversions on your cars with the community.