10.1  The myth of Triptane

[ This post is an edited version of several posts I made after JdA posted 
  some claims from a hot-rod enthusiast reporting that triptane + 4cc TEL 
  had a rich power octane rating of 270. This was followed by another 
  post that claimed the unleaded octane was 150.]

In WWII there was a major effort to increase the power of the aviation 
engines continuously, rather than just for short periods using boost fluids.
Increasing the octane of the fuel had dramatic effects on engines that could 
be adjusted to utilise the fuel ( by changing boost pressure ). There was a 
12% increase in cruising speed, 40% increase in rate of climb, 20% increase 
in ceiling, and 40% increase in payload for a DC-3, if the fuel went from 87 
to 100 Octane, and further increases if the engine could handle 100+ PN fuel
[134]. A 12 cylinder Allison aircraft engine was operated on a 60% blend of
triptane ( 2,2,3-trimethylbutane ) in 100 octane leaded gasoline to produce 
2500hp when the rated take-off horsepower with 100 octane leaded was 1500hp
[14].

Triptane was first shown to have high octane in 1926 as part of the General 
Motors Research Laboratories investigations [135]. As further interest 
developed, gallon quantities were made in 1938, and a full size production 
plant was completed in late 1943. The fuel was tested, and the high lead 
sensitivity resulted in power outputs up to 4 times that of iso-octane, and 
as much as 25% improvement in fuel economy over iso-octane [14]. 

All of this sounds incredibly good, but then, as now, the cost of octane 
enhancement has to be considered, and the plant producing triptane was not 
really viable. The fuel was fully evaluated in the aviation test engines, 
and it was under the aviation test conditions - where mixture strength is 
varied, that the high power levels were observed over a narrow range of 
engine adjustment. If turbine engines had not appeared, then maybe triptane 
would have been used as an octane agent in leaded aviation gasolines. 
Significant design changes would have been required for engines to utilise 
the high antiknock rating. 

As an unleaded additive, it was not that much different to other isoalkanes, 
consequently the modern manufacturing processes for aviation gasolines are 
alkylation of unsaturated C4 HCs with isobutane, to produce a highly 
iso-paraffinic product, and/or aromatization of naphthenic fractions to 
produce aromatic hydrocarbons possessing excellent rich-mixture antiknock 
properties.

So, the myth that triptane was the wonder antiknock agent that would provide
heaps of power arose. In reality, it was one of the best of the iso-alkanes 
( remember we are comparing it to iso-octane which just happened to be worse 
than most other iso-alkanes), but it was not _that_ different from other 
members. It was targeted, and produced, for supercharged aviation engines
that could adjust their mixture strength, used highly leaded fuel, and wanted
short period of high power for takeoff, regardless of economy. 

The blending octane number, which is what we are discussing, of triptane
is designated by the American Petroleum Institute Research Project 45 survey
as 112 Motor and 112 Research [52]. Triptane does not have a significantly 
different blending number for MON or RON, when compared to iso-octane. 
When TEL is added, the lead response of a large number of paraffins is well 
above that of iso-octane ( about +45 for 3ml TEL/US Gal ), and this can lead 
to Performance Numbers that can not be used in conventional automotive 
engines [14].
    
10.2  From Honda Civic to Formula 1 winner.                    

[ The following is edited from a post in a debate over the advantages of
water injection. I tried to demonstrate what modifications would be required 
to convert my own 1500cc Honda Civic into something worthwhile :-).]

There are many variables that will determine the power output of an engine. 
High on the list will be the ability of the fuel to burn evenly without 
knock. No matter how clever the engine, the engine power output limit is 
determined by the fuel it is designed to use, not the amount of oxygen 
stuffed into the cylinder and compressed. Modern engines designs and 
gasolines are intended to reduce the emission of undesirable exhaust 
pollutants, consequently engine performance is mainly constrained by the 
fuel available.

My Honda Civic uses 91 RON fuel, but the Honda Formula 1 turbocharged 1.5 
litre engine was only permitted to operate on 102 Research Octane fuel, and
had limits placed on the amount of fuel it could use during a race, the
maximum boost of the turbochargers was specified, as was an additional 
40kg penalty weight. Standard 102 RON gasoline would be about 96 (R+M)/2 if 
sold as a pump gasoline. The normally-aspirated 3.0 litre engines could use 
unlimited amounts of 102RON fuel. The F1 race duration is 305 km or 2 hours,
and it's perhaps worth remembering that Indy cars then ran at 7.3 psi boost.

Engine                 Standard         Formula One     Formula One 
Year                     1986              1987            1989
Size                   1.5 litre         1.5 litre       1.5 litre
Cylinders                 4                 6               6 
Aspiration              normal            turbo           turbo
Maximum Boost             -               58 psi          36.3 psi           
Maximum Fuel              -              200 litres      150 litres  
Fuel                    91 RON           102 RON         102 RON
Horsepower @ rpm      92 @ 6000         994 @ 12000     610 @ 12500
Torque (lb-ft @ rpm)  89 @ 4500         490 @  9750     280 @ 10000
   

The details of the transition from Standard to Formula 1, without 
considering engine materials, are:- 

1. Replace the exhaust system. HP and torque both climb to 100.
2. Double the rpm while improving breathing, you now have 200hp
   but still only about 100lb-ft of torque. 
3. Boost it to 58psi - which equals four such engines, so you have 
   1000hp and 500lb-ft of torque.

Simple?, not with 102 RON fuel, the engine/fuel combination would knock  
the engine into pieces, so....

4. Lower the compression ratio to 7.4:1, and the higher rpm is a
   big advantage - there is much less time for the end gases to
   ignite and cause detonation.
5. Optimise engine design. 80 degree bank angles V for aerodynamic 
   reasons, and go to six cylinders = V-6
6. Cool the air. The compression of 70F air at 14.7psi to 72.7psi
   raises its temperature to 377F. The turbos churn the air, and
   although they are about 75% efficient, the air is now at 479F.
   The huge intercoolers could reduce the air to 97F, but that 
   was too low to properly vaporise the fuel.
7. Bypass the intercoolers to maintain 104F.
8. Change the air-fuel ratio to 23% richer than stoichiometric
   to reduce combustion temperature.
9. Change to 84:16 toluene/heptane fuel - which complies with the 
   102 RON requirement, but is harder to vaporise. 
10.Add sophisticated electronic timing and engine management controls
   to ensure reliable combustion with no detonation.

You now have a six-cylinder, 1.5 litre, 1000hp Honda Civic.

For subsequent years the restrictions were even more severe, 150 litres
and 36.3 maximum boost, in a still vain attempt to give the 3 litre,
normally-aspirated engines a chance. Obviously Honda took advantage
of the reduced boost by increasing CR to 9.4:1, and only going to 15%
rich air-fuel ratio. They then developed an economy mode that involved
heating the liquid fuel to 180F to improve vaporisation, and increased
the air temp to 158F, and leaned out the air-fuel ratio to just 2% rich.
The engine output dropped to 610hp @ 12,500 ( from  685hp @ 12,500 and
about 312 lbs-ft of torque @ 10,000 rpm ), but 32% of the energy in
the fuel was converted to mechanical work. The engine still had crisp
throttle response, and still beat the normally aspirated engines that
did not have the fuel limitation. So turbos were banned. No other
F1 racing engine has ever come close to converting 32% of the fuel
energy into work [136].

In 1995 the FIA listed a detailed series of acceptable ranges for
typical components in racing fuels for events such as F1 races, along 
with the introduction of detailed chromatographic "fingerprinting" of 
the hydrocarbon profile of the fuel [137]. This was necessary to prevent
novel formulations of fuels, such as produced by Honda for their turbos.