NITROMETHANE AS A PISTON ENGINE FUEL 540186

An investigation has been carried out under conditions comparable to normal engine operation to ascertain the effects of an additive such as nitromethane on the power output, fuel consumption, and efficiencies which result therefrom. It has been learned that nitromethane can increase power output by as much as 13 percent on an indicated or gross basis when added to methyl alcohol and by 7 percent when added to a benzene-isooctane mixture in concentrations of 20% by volume. By so doing, the indicated specific fuel consumption increases, but contrary to expectations, so does the indicated thermal efficiency. The results from the benzene-isooctane blend were comparable to those from the methanol in all respects except for the increase in power, which was not as great.

The amount of nitromethane which can be added to a given fuel is a function of its tendency to bring about preignition in the engine. In the case of the addition to the base fuels used, this limit turned out to be a maximum of 20% by volume.

The increase in power which resulted from the use of nitromethane can be traced directly to the amount of additional energy which the additive makes available to the fuel-air mixture. While the increase in specific fuel consumption results from the fact that nitromethane has a much lower heating value than any of the other components of the fuel used, the increased thermal efficiency is thought to be a result of the increased temperatures and perhaps greater rate of combustion attendant to the use of the additive. The greater increase of indicated power obtainable with the methanol-nitromethane blend (13%) compared to the benzene-isooctane blend (7%) is due to the fact that in the former case more nitromethane can be introduced into the engine per stroke or per cubic foot of mixture before preignition takes effect, even though the volume amounts in the fuels are comparable.