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Cars are converted to propane or Liquefied Petroleum Gas (LPG) generally because their operating costs are much lower than for gasoline. Nowadays, automobile conversions are much more popular in Europe than in North America. Conversions were quite popular in Canada in the 1980s because of government incentive programs. In North America, the best candidates are vehicles in fleets driven long distances because the lower operating cost makes a faster payback in recovering the capital cost of conversion. The main concern in this type of conversion is cost and performance is a minor issue. The commercial grade of propane for automotive use is known as HD5 in North America. Although propane has a higher energy content (J/kg or BTU/lb) than gasoline, it has a lower density (kg/litre or lb/gallon). Because of its lower density, a car running on propane will have a higher fuel consumption than one running on gasoline but its higher energy content will compensate somewhat for the higher fuel consumption. When the fuel price is factored into consumption, the driving cost ($/km or $/mile), propane is significantly cheaper to use. An additional benefit of propane is that, as a cleaner burning fuel, fleet vehicles last much longer between overhauls. Propane does not produce carbon deposits in the combustion chamber no matter how long it is used. Without the carbon deposits, engines do not require higher octane fuels to compensate for the gradually increasing compression ratio or the hot spots that cause preignition. There is no carbon to blow by the rings to contaminate the oil, which allows the oil to remain clean. Engine oil at 10,000 km will look as clean as newly changed oil. The main problem with the oil is that extended distances between oil changes cause the lighter parts of the oil to boil off and the oil gradually becomes more viscous. A good place to start research for a propane conversion is Jay Storer's book: Economy or Performance Propane Fuel Conversions for Automotive Engines. It is published by S-A Design (ISBN 0-931472-12-1) but it appears to be out print now. A few book sellers still seem have it stock however. Cars converted to propane generally suffered a performance loss in the bad old carbureted days. The problem was that propane was metered (or fumigated) into the engine in a gaseous form. The fuel gas displaced air that the engine was drawing which caused a slight loss in volumetric efficiency. Gasoline is metered into the engine as an atomized liquid. The density of a liquid is much greater that that of a gas and so the volumetric efficiency loss compared to pure air is negligible. The other contributor to lower volumetric efficiency is in the restrictive mixer. 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 but we feel that it is better suited for large six cylinder engines and small V8s. 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 may help larger engines but we have not found this information yet. From the information we have been able to find by searching the internet, carbureted race cars are very uncommon. There is one racer of note: Richard Rowe. You may find more information on his web site: http://www.alternatefuelsracing.com/. 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 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. 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 (http://www.gas-injection.com/) has done a great deal of work with gaseous propane fuel injection. They are also one of the few companies that have already built propane-fuelled race cars. Please check the side navigation bar under GIT for more information that they were able to provide me. In Canada, Yugo-Tech (http://www.yugo-tech.com/) is another company developing gaseous propane injection but they are more focussed on fleet conversions. Yugo-Tech 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. This system uses the manufacturers on board computer to drive a second set of injectors but they interface the signal and modify the injector pulse width to suit the alternate fuel. In this manner they "mirror" the manufacturers fueling strategy so the check engine light does not come on every time the computer performs a system check. 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. Please follow this link to read more: http://www.caranddriver.com/article.asp?section_id=26&article_id=2279&page_number=1. |
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