Thursday, February 14, 2008

The Truth About Vapor Fuel

Like many others, we have heard stories of vapor systems that achieved incredible mileage. We have spent the last seven years, and a great deal of our client’s money, to determine what actual benefit, if any, there is to fuel vapor technology.

We found that fully vaporizing fuel prior to entering the combustion chamber is beneficial in several ways including a more homogenous fuel-air mix and a faster flame speed. Both of those proved to be very important when we were in a lean-burn condition. We were able to safely run a standard V-8 engine on fuel vapor at air to fuel ratios up to 28-1 rather than the standard 14.7-1.

The impact of lean-burn combustion on fuel economy is well documented. Several of the major automakers experimented with lean-burn during the nineties and into this century. There are credible reports of as much as a 50% increase in fuel economy. We were also able to demonstrate the same benefit using a vapor fuel system in a lean-burn mode.

So what happened to that technology? The inability of current catalytic converters (CATS) to remove Oxides of Nitrogen (NOx) from the exhaust has prevented its use. It seems the CATS work fine at the normal air to fuel ratio but cannot remove NOx in a lean condition. A great deal of time and money has been spent in the last decade, on a variety of theories, attempting to solve the NOx issue.

Although we, and much of the automotive world, found the best fuel economy is achieved at an air to fuel ratio of about 20-1 the NOx levels decreased to acceptable levels at about 28-1. The fuel vapor system allowed us to run that lean without requiring the complicated and expensive engine modifications of the direct injection systems. The problem everyone seems to have experienced was a significant loss of power during that extreme lean condition. A more efficient combustion was needed if any of the benefit of lean-burn was to be realized.

Homogeneous Charge Compression Ignition (HCCI) and Autoignition are two of the most touted current technologies that may fit the bill. General Motors and Ford have both announced plans to produce vehicles that will utilize HCCI technology. We agree but this is where we have taken a different approach. It appears the rest of the auto industry has approached HCCI and Autoignition as extensions of the lean-burn effort, but we have not.

The HCCI efforts of others appear to still be based on diluting the amount of fuel used by supplying more air to the charge resulting in a lean fuel to air condition. The greatly improved efficiency of the HCCI combustion allows their technology to work at higher air to fuel ratios where NOx is not as much an issue but not without sacrificing power. Automakers are reporting their HCCI operation will be used at light loads and lower speeds. They are further predicting an improvement in fuel economy of between 15 and 30%.

Vapor Fuel Technologies, LLC (VFT) has a system that utilizes the benefit of HCCI type combustion without creating the NOx problem. Vaporizing the fuel and mixing with heated air prior to entering the combustion chamber accomplish the dilution of the fuel air charge. This process accomplishes the dilution by thermal expansion rather than adding air. The heated air and vaporized fuel simply occupy more space, per pound, within the combustion chamber.

Dilution by thermal expansion allows the VFT System to operate at the standard, 14.7-1, air to fuel ratio allowing the catalytic converter to work correctly. The heating process also creates the conditions for a spark initiated autoignition combustion. As the fuel air charge is compressed it approaches the point of autoignition. When the spark plug ignites, the in-cylinder pressure and temperature rapidly increases. The homogeneous vapor mixture rapidly combusts in a series of autoignition events.

The result of the technology is an independently verified increase of over 30% in fuel economy. An EPA recognized and California Air Resources Board (CARB) certified laboratory ran a series of tests and has verified the fuel economy improvement.

As for the original question about any real improvement due to vaporizing fuel, we have not discovered any 200mpg carburetors but there are proven benefits.

You can find out more about the company that developed this technology for Vapor Fuel Technologies at our website Bushnell Engineering or the system itself at Vapor Fuel Technologies