CNG has been extensively used in Italy and New Zealand ( NZ had 130,000 dual-fuelled vehicles with 380 refuelling stations in 1987 ). The conversion costs are usually around US$1000, so the economics are very dependent on the natural gas price. The typical 15% power loss means that driveability of retrofitted CNG-fuelled vehicles is easily impaired, consequently it is not recommended for vehicles of less than 1.5l engine capacity, or retrofitted onto engine/vehicle combinations that have marginal driveability on gasoline. The low price of crude oil, along with installation and ongoing CNG tank-testing costs, have reduced the number of CNG vehicles in NZ. The US CNG fleet continues to increase in size ( 60,000 in 1994 ).
LPG ( Liquified Petroleum Gas ) is predominantly propane with iso-butane and n-butane. It has one major advantage over CNG, the tanks do not have to be high pressure, and the fuel is stored as a liquid. The fuel offers most of the environmental benefits of CNG, including high octane. Approximately 20-25% more fuel is required, unless the engine is optimised ( CR 12:1 ) for LPG, in which case there is no decrease in power or increase in fuel consumption [27,118]. There have been several studies that have compared the relative advantages of CNG and LPG, and often LPG has been found to be a more suitable transportation fuel [118,120].
methane propane iso-octane ======= ======= ========== RON 120 112 100 MON 120 97 100 Heat of Vaporisation (MJ/kg) 0.5094 0.4253 0.2712 Net Heating Value (MJ/kg) 50.0 46.2 44.2 Vapour Pressure @ 38C ( kPa ) - - 11.8 Flame Temperature ( C ) 1950 1925 1980 Stoich. Flame Speed. ( m/s ) 0.45 0.45 0.31 Minimum Ignition Energy ( mJ ) 0.30 0.26 - Lower Flammable Limit ( vol% ) 5.0 2.1 0.95<> Upper Flammable Limit ( vol% ) 15.0 9.5 6.0 Autoignition Temperature ( C ) 540 - 630 450 415 <>
The technology to operate IC engines on hydrogen has been investigated in depth since before the turn of the century. One attraction was to use the hydrogen in airships to fuel the engines instead of venting it. Hydrogen has a very high flame speed ( 3.24 - 4.40 m/s ), wide flammability limits ( 4.0 - 75 vol% ), low ignition energy ( 0.017 mJ ), high autoignition temperature ( 520C ), and flame temperature of 2050 C. Hydrogen has a very high specific energy ( 120.0 MJ/kg ), making it very desirable as a transportation fuel. The problem has been to develop a storage system that will pass all safety concerns, and yet still be light enough for automotive use. Although hydrogen can be mixed with oxygen and combusted more efficiently, most proposals use air [114,119,121-124].
Unfortunately the flame temperature is sufficiently high to dissociate atmospheric nitrogen and form undesirable NOx emissions. The high flame speeds mean that ignition timing is at TDC, except when running lean, when the ignition timing is advanced 10 degrees. The high flame speed, coupled with a very small quenching distance mean that the flame can sneak past inlet narrow inlet valve openings and cause backflash. This can be mitigated by the induction of fine mist of water, which also has the benefit of increasing thermal efficiency ( although the water lowers the combustion temperature, the phase change creases voluminous gases that increase pressure ) and reducing NOx . An alternative technique is to use direct cylinder induction, which injects hydrogen once the cylinder has filled with an air charge, and because the volume required is so large, modern engines have two inlet valves, one for hydrogen and one for air . The advantage of a wide range of mixture strengths and high thermal efficiencies are matched by the disadvantages of pre-ignition and knock unless weak mixtures, clean engines, and cool operation are used.
Interested readers are referred to the group sci.energy.hydrogen and the " Hydrogen Energy" monograph in the Kirk Othmer Encyclopedia of Chemical Technology , for recent information about this fuel.
As water-gasoline fuels have been extensively investigated [113,129], interested potential investors may wish to refer to those papers for some background. Mr. Gunnerman appears to have modified his claims a little with his new A55 fuel. A recent article claims a 29% increase in fuel economy for a test bus in Reno, but also claims that his fuel combusts so efficiently that it can pass an emissions test without requiring a catalytic converter . Caterpillar are working with Gunnerman to evaluate his claims and develop the product.
Relevant properties include : Avgas Propylene Oxide 100/130 115/145 Density (g/ml) 0.828 0.72 0.74 Boiling Point (C) 34 30-170 30-170 Stoichiometic Ratio (vol%) 4.97 2.4 2.2 Autoignition Temperature (C) 464 440 470 Lower Flammable Limit (vol%) 2.8 1.3 1.2 Upper Flammable Limit (vol%) 37 7.1 7.1 Minimum Ignition Energy (mJ) 0.14 0.2 0.2 Nett Heat of Combustion (MJ/kg) 31.2 43.5 44.0 Flame Temperature (C) 2087 2030 2030 Burning Velocity (m/s) 0.67 0.45 0.45
4CH3NO2 + 3O2 -> 4CO2 + 6H20 + 2N2
The nitromethane Specific Energy at stoichiometric ( heat of combustion divided by air-fuel ratio ) of 6.6, compared to 2.9 for iso-octane, indicates that the fuel energy delivered to the combustion chamber is 2.3 times that of iso-octane for the same mass of air. Coupled with the higher flame temperature ( 2400C ), and flame speed (0.5 m/s), it has been shown that a 50% blend in methanol will increase the power output by 45% over pure methanol, however knock also increased .
Temperature Flame Speed Fuel Oxidant ( C ) ( m/s ) Acetylene Air 2400 1.60 - 2.70 " Nitrous Oxide 2800 2.60 " Oxygen 3140 8.00 - 24.80 Hydrogen Air 2050 3.24 - 4.40 " Nitrous Oxide 2690 3.90 " Oxygen 2660 9.00 - 36.80 Propane Air 1925 0.45 Natural Gas Air 1950 0.39<>Nitrous oxide is not yet routinely used on standard vehicles, but the technology is well understood.
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 . 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 .
Triptane was first shown to have high octane in 1926 as part of the General Motors Research Laboratories investigations . 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 .
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 . 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 .
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 @ 10000Lets consider the transition from Standard to Formula 1, without considering materials etc.
Simple?, not with 102 RON fuel, the engine would detonate to pieces. so..
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 .
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 .