In North America, a common option for a dedicated or straight propane option on older cars was the Impco CA425 mixer. A mixer becomes a carburetor when it is fitted with throttle valves. For the larger American cars that could benefit from propane operation, Impco recommends this mixer for up to 450 CID engines. This mixer is rated for 460 CFM @1.5" Hg but this may in practice be restrictive for big block engines. It should be quite suitable for engines such as the Chevrolet 350 CID (5.7 liter) engine. The shape of the gas jet in Impco mixers controls the fuel mixture so that it becomes richer as air flow increases. A different gas jet is available for larger engines (over 370 CID), which is leaner at their higher air flows. Even though the fuel mixture may be leaner at higher flows, it really means that the fuel mixture is closer to the ideal fuel mixture required to achieve the best power and economy. Rich fuel mixtures in gaseous fuels, unlike with gasoline, result in detonation and burned valves.
From the information we have been able to find by searching the internet, propane-carbureted race cars are very uncommon. Richard is one racer we have been able to find. You may find more information on his web site: http://www.alternatefuelsracing.com/. As a racer, sponsorship is always welcome so don't be shy to put your name on his car.
However, one great way to take advantage of the potential of propane is through turbocharging. The turbocharger overcomes the loss in volumetric efficiency and the higher octane rating of 104 allows higher boost pressures. Ak Miller of California was the one most known in doing a lot of development of turbocharged propane engines in the sixties and seventies and Jay Storer features him prominently in the turbocharger chapter of his book.
Nowadays, with modern vehicles being equipped with digital fuel and ignition control and port fuel injection, sequential fuel injection of propane overcomes the volumetric efficiency disadvantages of the propane mixer. Digital fuel and ignition control is a feedback control system. The engine's computer has a preprogrammed plan for controlling the fuel mixture and spark advance as a function of various parameters measured by sensors in the engine. The O2 or Oxygen sensor in the exhaust, for example, tells the computer how much to correct the fuel mixture to the target mixture. A far better means than the best guess provided by the manufacturer in the design of the shape of the gas valve or the size of the metering jets in the carburetor. Impco and Dual Curve both offer feedback systems for controlling propane fumigation carburetors.
As there is no longer a carburetor on modern engines, propane fuel injection would be the logical option for conversions. There is a great deal of development work currently going on in the area of sequential propane injection. There are two means of injecting propane: gaseous and liquid. Each has its advantages but liquid injection has the potential for higher performance . The reason for this is that as a liquid, propane must absorb heat from the air to evaporate which causes the air to cool and become denser. The increased air density effectively increases the volumetric efficiency of the engine and increased volumetric efficiency is the goal of every engine performance modification.
There are several companies world-wide developing systems for gaseous propane injection and these systems are designed to seamlessly integrate with the engine's control system. Either the injectors replace the gasoline injectors for dedicated operation or the propane injectors supplement the gasoline injectors for dual fuel operation. These systems are the natural evolution of the fumigation system to allow the computer to precisely control the fuel mixture.
Gas Injection Technologies Pty Ltd of Australia had done a great deal of work with gaseous propane fuel injection. They were also one of the few companies that have already built propane-fuelled race cars. GIT has provided us with some additional information than what is available on their web site. Unfortunately, their system was not yet available in North America and seem to gone out of business.
In Canada, EDPRO and Technocarb are companies specializing in gaseous propane injection. While both are focused on fleet conversions, Technocarb has a much wider product range. The systems of each manufacturer uses the vehicle's on-board computer (PCM) to drive a second set of injectors but alterative fuel system's controller intercepts the signal and modifies the injector pulse width to suit the alternative fuel. In this manner they "mirror" the manufacturers fueling strategy so the check engine light does not come on when the computer performs a system check.
EDPRO is an alternate fuel designer, manufacturer, supplier and installer of both LPG (Propane) and CNG (Natural Gas). They are also starting to get involved in hydrogen. Their proprietary system is known as SEQUIN and the name SEQUIN is an acronym for SEQUential INjection. The SEQUIN system uses a heat exchanger to heat the fuel in the LPG tank, which allows their system to operate in extreme cold conditions. By withdrawing only vapour from the fuel tank, EDPRO also claims this system eliminates the potential for ‘heavy ends’ contamination of control components. However, the SEQUIN system is only available for Ford 4.6L and 5.4L vehicle platforms.
Technocarb has many conversion systems for North American domestic vehicles and a number of universal systems. The majority of their systems are for LPG but they have a few natural gas applications as well. To meet current EPA certification requirements, Technocarb has developed their own Sequential Vapour Injection (SVI) LPG injection system, which available for North American domestic applications as well as in universal kits for other fuel injected vehicles. Rather than circulating warmed LPG fuel through the fuel tank, Technocarb simply allows the engine to remain in gasoline operation mode if the tank pressure (due to low ambient temperature) is too low. Technocarb addresses the 'heavy ends' issue by providing an optional vapour temperature controller if warranted by poor fuel quality.
Car and Driver magazine ran an article about a propane injected police car in their July 2002 issue. This car used a liquid propane injection system, which made the transplanted V10 truck engine much quicker than the stock 4.6 litre gasoline engine.
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