swan

'ello all,

Interesting reading at http://wrxhackers.com/alchystuff/

Alcohol is a safe additive to use. Since the 1960s, all cars have been manufactured with alcohol resistant hoses, connections, O-rings, seals, and plastics. This was necessary because of the popular use of alcohol base gas line antifreeze additives, and the use of ethanol mixes in automotive fuel. But, the biggest advantage of alcohol injection is that it is an "on demand" system for both the street, or strip. Especially for street applications, the realities are that, for most drivers, less than 2 percent of the time high turbo boost is actually used. So, the argument becomes: Why have the fuel tank filled with high price race gas, or add a couple of gallons of toluene with every tank, when the higher knock threshold protection is only needed for those relatively brief events closer to WOT? Tuning with alcohol injection only for those boost levels when it's really needed to raise the knock threshold (higher octane equivalent) also accounts for the small quantities of alcohol consumed.

Tuning to the edge of the envelope quickly bumps into the knock limits of the fuel being used. Alcohol injection can increase the knock threshold of 91-93 octane pump gas to the equivalent of the range of 104-108 octane. The relatively small amounts of alcohol injected doesn't increase the total fuel energy much, and only adds small amounts of additional oxygen. While methanol alcohol has an equivalent octane rating of 108, the main effect is the result of large, rapid evaporatative cooling of the intake air. Also, small amounts of water added help control the flame front in the cylinder for smooth, controlled cylinder pressure rises at ignition (the opposite of knock). This effect also shows up as a very significant reduction of 60 to 100 degees (F) of the EGT at WOT. The cooling effect of alcohol is also used on supercharged (up to 8 pounds boost) engines with no IC. The effect is like adding an intercooler. Alcohol injection is a very mature technology that has been in widespread use, especially since WWII, with lots of experience, and data availble. There is no need to re-invent the wheel, or plow any new ground. It is a reliable, cost effective way, to raise the knock threshold of the fuel being used. So, the answer to the question: "Why alcohol injection?" is simply "Why not?"

Andy.F

I used a home made version not unlike this for drag racing. It was also ideal for chilling the intake manifold down whilst sitting in the staging lanes