Thanks: 
Likes: 
Gasoline
With the unending interest in fuel on Hydroracer.net and Screamandfly.com, I think a technical thread about fuel would be interesting here as well.
In each boat racing category and governing body there seem to be different rules regarding gas. Gasoline will be a topic of discussion at this year's APBA Annual Meeting in Ft Lauderdale, FL..
A lot of racers are under the spell of the idea that there may be a magic formula or additive being used by the the guys that beat them.
Here is what I have learned over many years of research from countless sources:
Going back in history, before there really was commercial car gasoline ... the predicessor of what we now know as gasoline was basically used as cleaning solvent. Many early car makers recommended benzene as fuel and benzene was available a lot of places as car fuel. Benzene is pretty toxic and fell out of favor about 100 years ago in favor of less toxic gasoline. One of the problems with gasoline refined from petroleum is that the end result varies due to the source ... like water from a spring diluted with various minerals, gasoline refined from crude oil varies, too. Some spring water is tasty and in great demand, other springs are polluted with sulphur and no one would dare drink it ... even if they could get past the smell. Some crude oil stocks make pretty good gasoline, others make gasoline only suitable to use as cleaning solvent.
The nature of the combustion process:
During World War I there was a great leap forward in engine technology. Most of it based on the demand to produce very light and very powerful engines for airplanes. For some time the prevailing thought was that all fuels actually burned the same way .... that the only differences were in how they were physically delivered to the engine. They thought if you could properly deliver melted wax to an engine, it could be made to produce the same power as gasoline, kerosene or alcohol. Even though this is quite wrong the majority of researchers believed it. Thomas Midgely was one of these researchers. While working on what he thought was improved delivery of medium grade gasoline by doping it with dye, he stumbled upon proof that it was the exact ingredients of the fuel that made a difference in whether it could be used in a high output engine and that small quanitites of doping agents could make fuels behave differently. Charles Kettering of GM was also pivitol in this research field. Their research turned the combustion research world on its ear and eventually lead to leaded gasoline and the octane rating scale.
Research during WWII produced even more gains in combustion research, but more importantly refining process to make huge quanitities of high grade gasoline. Before WWII many cars had manual carb adjustments and separate manual spark advance controls where the driver could reach them on the dash. Motorcycles had them too. During WWII incredible amounts of very consistant gasoline were made for the daily bombing raids in Europe. Hundreds of planes flew daily, sometimes thousands and the engines were very thirsty. Motor sizes ran from 1,300 cubic inches to nearly 3,000 on planes that had 2 or 4 engines. After WWII there was a great reduction in demand for gasoline, but the refineries that made the high quality, super conisistant gas where still around. Rather than going back to the old processes the gas companies converted their wartime refineries to make commercial gasoline. Suddenly the gasoline market was full of superior quality gasoline. Little by little cars stopped having manual spark advance and fuel adjustments ... including having automatic chokes. Carl Kiekhaefer took advantage of the improved consistancy of gas and did away with high speed carb adjusters and manual spark advance controls. This was not possible with the erratic quality of gasoline available before WWII.
Let's jump back to the WWI era. Once they became certain it was something in the nature of each molecule that determined how well it performed under increasing pressure, they developed a standardized test and special test motor. The test scale compares the fuel in question to a 7 carbon straight chain connected (all 7 carbon atoms one after another) heptane ("normal" heptane or n-heptane) and a branched isomer of octane (iso-octane, more correctly described by the organic chemistry name 2,2,4-Trimethylpentane) with 8 carbon atoms arranged more like a snowflake than a chain. n-heptane was declared zero on the scale and iso-octane was declared 100. Performance between zero and 100 relates to performance equal to mixtures of n-heptane and iso-octane. Gasoline rate 50 on the octane scale performs like a 50/50 mixture of heptane and octane, 87 performs like 13% heptane and 87% octane, gas rated 95 performs like 5% heptane and 95% octane. Plotted out on a graph the mixtures make a nice curve ... if you extend the performance curve beyond the performance of 100% iso-octane you can accurately place numbers over 100. In actual testing, numbers over 100 are accurately placed by comparing against iso-octane with a certain amount of tetra-eythl lead for each run.
Tetra ethyl lead is a synthetic chemical made just for improving the performance of gasoline. Once Charles Kettering was certain lead was the best choice as an additive, he had GM join forces with Standard Oil of New Jersey in 1923 to form General Motors Chemical Corporation. A year later, the company became Ethyl Gasoline Corporation and finally, Ethyl Corporation in 1942 based in Richmond, VA. Tetra ethyl lead by itself eats away at exhaust valves and seats in 4 stroke motors. To counter this ethyl bromide is added along with tetra ethyl lead. There are chemicals that increase octane numbers of gasoline better than lead, but they are much more toxic than lead. There are some chemicals that are close but not quite as good as lead based additives, too (and they were popularly available in the 1980's and 1990's but not any more). Anniline oil was one of the better octane improving additives available 15 to 20 years ago, but it is generally not available these days as well due to concerns over its toxicity as well. The important thing to be aware of is that all of these chemicals are strong poisons and would have to be handled as such. A less poisonous octane improver is alcohol, but it is not nearly as strong at improving octane rating compared to lead, anniline or the other stronger chemicals. To get a true octane increase with alcohol you would have to add quarts or gallons to a tank of car gas.
Time to bring in another character to the story: Harry Ricardo. Ricardo believed in the current threory when it was considered quackery. When Kettering, Midgely and all proved otherwise - Ricardo was well ahead of most other researchers. In short order Ricardo developed a special test engine for evaluating the knock performance of fuels. This special engine can have its compression ratio changed while underway rather than using separate engines with different compression ratios or by stopping the engine and changing the cylinder head to change the compression ratio. Originally they just listened for audible knock sound. Little by little the testing became more precise with things like bouncing pins connected to wires to change the subjective "I can hear some knock" to a very precise "the meter says knock has begun" and changing "I think what we hear now is severe knock" to "the meter indicates the exact same severe knock we heard with the other fuel". Now that they had measurement of knock down to a science they wanted to learn exactly what they were hearing really was. Special engines with glass lenses were built and special high speed photography was developed. This research was one of the very first applications of high speed photography.
Once it was all captured on film and documented, even more facts became known. High speed imagery clearly showed that pressure related knock sound was not due to fuel igniting before the spark plug fired. Instead it was due to a second flame starting in the combustion chamber after the normal combustion started.
With preignition as a separate type of event, another special engine was set up to check various fuel's performance regarding preignition. This engine had a heater built into the head to simulate a hot spot in the combustion chamber. Many fuels that were rated high on the octane scale also resisted hot spot ignition ..... but not all of them. Some fuels that were only so so at resisting knock were almost impossible to ignite with the hot wire. It became obvious that preignition characteristics and knock characteristics were not directly related.
High speed photography also showed that knock resistance (high octane rating) was also not directly related to flame speed. Some high octane fuels burned faster than others, some burned slower and the same thing for less knock resistant fuels, some burn fast, some burn slower ... flame speed and knock resistance are separate qualities.
Reply With Quote
The ? Of Fuel - By John Copeland
Bookmarks