NASCAR Goes From Leaded 112 to Unleaded 98
|Q&A with Mark McArdle on Unleaded Fuel|
|What impact does the unleaded fuel have on the performance, horsepower and durability of the engine?
The performance of the engine is affected in only one significant way. The loss of tetraethyl lead dictates that unleaded fuel must use alternate chemical compounds to raise the octane rating of the fuel to an acceptable level. The new unleaded fuel has an octane rating of 98, whereas the older leaded fuel has a 112 rating. The octane number is a measure of a fuel's resistance to the phenomenon of detonation. Detonation is the premature ignition of the fuel air mixture in the engine's combustion chambers and it is an extremely destructive force. As a result the engine must be tuned for absolutely precise air-fuel ratio and spark timing.
The horsepower production is unaltered by the fuel change. This is due to the energy content of the fuel being unchanged. Hydrocarbon fuels measure energy content in BTU/lb.(British Thermal Units per pound of fuel) The value for both fuels is approximately 18,000 BTU/lb. Because each fuel contains the same amount of chemical energy, each is capable of the same power production.
The greatest concern we have with the fuel change is the durability consideration. Tetraethyl lead, while environmentally unsafe, has the desirable property of self lubrication. Our greatest concern is with valve guide and valve seat wear. So far, neither has been a concern. The other potential area of problems is material compatibility. Fuel lines, fuel cell bladders, fuel pump diaphragms and carburetor parts all must be validated for the new fuel. While the energy content of the fuel is constant, the constituent chemical elements of the fuel are not. Some of the new blend chemicals have shown themselves to be highly corrosive and act as destructive agents when exposed to certain materials.
What design changes did you have to make to accommodate this switch?
The only design changes we have made to date are specific component design changes. In most cases this is due to the material to fuel compatibility issue mentioned above.
Did you see any dramatic impact on the engines once you analyzed them after the St. Louis race?
Dramatic would not be the description, but we have seen differences. Most of the evidence witness of combustion byproducts we are not used to seeing. This is due to the altered chemical reaction of the fuel blend. We were very conservative in tuning the engines at St. Louis and so the resultant byproducts deposited were greater in volume than we were used to seeing. We have subsequently become more and more aggressive in tuning and this problem is slowly disappearing.
How much of an environmental impact does this change have?
A tremendous amount. Tetraethyl lead is highly toxic and can lead to a lot of health issues. It is also responsible for the high level of oxides of nitrogen we used to have in the atmosphere as a result of its widespread use prior to the ban on unleaded gasoline for street use. Vapor emissions are also reduced with unleaded fuel.
How long have you been working to prepare for this change?
We have been working on the issue for 11 months.
Did you have to scrap existing engines or just modify them?
We only had to do slight modification to the core engine package. The components we scrapped were those unsuited to the new fuel by material properties.
What was the average cost per engine?
Did you do a lot of modeling to determining what would happen before you actually ran the engines with unleaded fuel?
No. Simulation in the combustion chamber level is very complex and requires coupled simulation. We have our UK arm, Advanced Engine Technology, working on that problem. Dr. Bryan Fleck of our AET staff is a specialist in this area and this type of modeling is his current research focus.
What kind of on-track testing did you do?
Actually, none. We did all of our testing in the test cell environment. We were able to simulate at track conditions with some precision and then we ran the race simulation in the controlled environment of our endurance test cell.
Have you explored any other fuels such as biodiesel or ethanol?
No we have not. While such research is interesting and environmentally beneficial, we lack the resources to dedicate to it unless NASCAR mandates it as a rule change.
What would be the challenges in running on those fuels?
The challenges in dealing with alternate hydrocarbon fuels are going to be similar. Pure ethanol, for example, has vastly different energy content than gasoline. As a result, significant changes need to be made to achieve best power-air fuel ratio settings. The specific gravity or mass per liter or gallon of each fuel is different and this can lead to some problems as well.
What do you see as the biggest impact for the teams and the sport? Cost-savings? Environmental benefits? Safety?
The answer is all of the above. I don't know if it will be possible to make a value judgment about that question for a while. Experience will tell us what the true impact has been, but maybe the most important impact for NASCAR as an industry in the sports entertainment marketplace will be viability of our series in overseas markets where unleaded fuel use is governmentally mandated for motor sport.
Are there any other changes in technology you would like to see NASCAR make in regards to the engine program?
I think the legalization of engine management systems would be great. While the use of electronics opens us up to the specter of cheating in a new area, if policed and controlled, I feel that we could see a benefit all out of proportion to the cost and difficulty of enforcement. A 'Green' NASCAR might bring in a whole new group of fans and sponsors.
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