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Bi-fuel vehicle

Vehicle capable of running on two fuels

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  • 5 chapters

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The most common technology and alternate fuel available in the market for bi-fuel gasoline cars is autogas (LPG), followed by natural gas (CNG), and it is used mainly in Europe. Poland, the Netherlands, and the Baltic states have many cars running with LPG. Italy currently has the largest number of CNG vehicles, followed by Sweden. They are also used in South America, where these vehicles are mainly used as taxicabs in main cities of Brazil and Argentina. Normally, standard gasoline vehicles are retrofitted in specialized shops, which install the gas cylinder in the trunk and the LPG or CNG injection system and electronics. The conversion is possible because the gases can use the spark ignition of a gasoline engine.

Diesel conversions

A Diesel engine is a compression-ignition engine and does not have a spark plug. To operate a diesel engine with an alternate combustible fuel source such as natural gas, a dual-fuel system is used with natural gas as the main fuel while diesel fuel is used for the ignition of the gas/air mixture inside the cylinder. In other words, a portion of diesel is injected at the end of the compression stroke, thereby maintaining the original diesel operation principle. (Running gas-only is possible but requires more extensive modification.)

Dual-fuel operation in this case means the engine uses two fuels (gas and diesel) at the same time, as opposed to bi-fuel, which would mean the engine could have the option of using either fuel separately.

There usually two type of conversions – low-speed (below 1000 RPM) and high-speed (between 1200 and 1800 RPM).

Low- and middle-speed conversion

Gas is injected into the cylinder inlet manifold by individual gas electromagnetic valves installed as close to the intake valves as feasible. The valves are separately timed and controlled by the injection control unit. This system interrupts the gas supply to the cylinder during the long overlap period of the intake and exhaust valves both being open (typical for slow-speed and medium-speed engines – within the valve overlap, cylinder scavenging is performed). This avoids substantial gas losses and prevents dangerous gas flow to the exhaust manifold.

  • This conversion is for low-speed engines up to 1000 RPM.
  • The system converts industrial diesel engine to bi-fuel operation by substitution of 70–90% natural gas for diesel or HFO.
  • Gas is injected directly before intake valve by high-speed electromagnetic injector, one or two injectors per cylinder.

High-speed conversion

Gas is mixed with air by a common mixer installed before any turbocharger(s). Gas flow is controlled by a throttle valve, which is electronically operated by the special control system according to the required engine output and speed. In order to avoid knocking of the engine, a knocking detector/controller is installed, thus enabling engine operation at the most efficient gas/diesel ratio.

  • Suitable for all high-speed engines, 1200–1800 RPM
  • The system converts industrial diesel engine to bi-fuel operation by substitution of 50–80% natural gas for diesel.
  • Gas and air are blended after the air filter and before the turbocharger by a central mixer.

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