|MadSci Network: Engineering|
This a a difficult question to answer in detail. There are a number of alternate fuels to gasolene. Each of them have advantages and disadvantages from an energy content, handling, storage, and environmental effects. I've listed a number of web sites below that go into some of this in detail. The first one lists the energy content of each and a comparison to gasolene. This would answer your last question, assuming equal efficiency of your engine when run on each type of fuel. The true way to measure the power of the engine is to run it on a dynamometer, which measures the power output of the engine at any moment. It is actually a huge brake which measures the instantaneous torque of the engine. A car alternator could perhaps be used as a dynamometer if you could add an electrical load to its terminals. Keep in mind, whatever you use, all of the energy absorbed by the dynamometer will end up as heat, and there will be a lot generated in only a few seconds. I tired to build one when I was about your age, and failed miserably. Exactly how to modify the engine seems more difficult to obtain. There are manufacturers who sell cars which run on dual fuels like gasolene and methanol or liquified natural gas. I know that the German army used methenol type fuel during WWII because of their gasolene shortage. I believe that any alcohol can have a bad effect on hoses, etc if the materials are not designed for it. Since Indy cars have been using it, it can be done, but may be more expensive than it is worth. There is also the flammibility and other safety related issues that make converting an engine by yourself something not advisable for the amatuer. I would recommend you look up Mother Earth News magazine back issues and see if anyone has tried doing it themselves. I could not find a web site devoted to the magazine or anyone who had done what you're asking, but I didn't look through all of the umpteen thousand web pages identified by the search engines either. If you can determine what fuel interests you (from a cost or availability viewpoint), you might contact companies or universities that are working on it and see if they can help you. Whatever you do, make sure an adult checks out what you want to try before trying it, as these fuels can be dangerous if you are not aware of the hazards. REFERENCES http://www.energy.ca.gov/afvs/vehicles.html#500 Table of alternate energy content and comparison to gasolene http://www.aiche.org/docs/government/altfuelAppend.htm http://www.concawe.be/HTML/VOLUME5/Alternat.htm Describes advantages and disadvantages of alt fuels http://www.energy.ca.gov/afvs/m85/methanolhistory.html Good description of use of methanol in cars http://www.as.wm.edu/Faculty/Klavetter/jcrenn/biosource.htm Discussion of biosource fuels http://www.mustangworks.com/articles/faqs-n-tech/gasfaq.shtml "What are the differences between an NGV and a regular gasoline-powered model? Are different parts used? The primary difference is in the fuel storage and intake system. Natural gas vehicles hold the gas in high pressure cylinders. From here, the gas travels along a high pressure fuel line leading to the engine compartment. With bi-fuel vehicles, the CNG tanks and lines are in addition to the conventional gasoline components." 9.3 What are the advantages of alcohols and ethers? This section discusses only the use of high ( >80% ) alcohol or ether fuels. Alcohol fuels can be made from sources other than imported crude oil, and the nations that have researched/used alcohol fuels have mainly based their choice on import substitution. Alcohol fuels can burn more efficiently, and can reduce photochemically-active emissions. Most vehicle manufacturers favoured the use of liquid fuels over compressed or liquified gases. The alcohol fuels have high research octane ratings, but also high sensitivity and high latent heats [6,17,51,74]. Methanol Ethanol Unleaded Gasoline RON 106 107 92 - 98 MON 92 89 80 - 90 Heat of Vaporisation (MJ/kg) 1.154 0.913 0.3044 Nett Heating Value (MJ/kg) 19.95 26.68 42 - 44 Vapour Pressure @ 38C (kPa) 31.9 16.0 48 - 108 Flame Temperature ( C ) 1870 1920 2030 Stoich. Flame Speed. ( m/s ) 0.43 - 0.34 Minimum Ignition Energy ( mJ ) 0.14 - 0.29 Lower Flammable Limit ( vol% ) 6.7 3.3 1.3 Upper Flammable Limit ( vol% ) 36.0 19.0 7.1 Autoignition Temperature ( C ) 460 360 260 - 460 Flash Point ( C ) 11 13 -43 - -39 The major advantages are gained when pure fuels ( M100, and E100 ) are used, as the addition of hydrocarbons to overcome the cold start problems also significantly reduces, if not totally eliminates, any emission benefits. Methanol will produce significant amounts of formaldehyde, a suspected human carcinogen, until the exhaust catalyst reaches operating temperature. Ethanol produces acetaldehyde. The cold-start problems have been addressed, and alcohol fuels are technically viable, however with crude oil at <$30/bbl they are not economically viable, especially as the demand for then as precursors for gasoline oxygenates has elevated the world prices. Methanol almost doubled in price during 1994. There have also been trials of pure MTBE as a fuel, however there are no unique or significant advantages that would outweigh the poor economic viability . 9.4 Why are CNG and LPG considered "cleaner" fuels. CNG ( Compressed Natural Gas ) is usually around 70-90% methane with 10-20% ethane, 2-8% propanes, and decreasing quantities of the higher HCs up to butane. The fuel has a high octane and usually only trace quantities of unsaturates. The emissions from CNG have lower concentrations of the hydrocarbons responsible for photochemical smog, reduced CO, SOx, and NOx, and the lean misfire limit is extended . There are no technical disadvantages, providing the installation is performed correctly. The major disadvantage of compressed gas is the reduced range. Vehicles may have between one to three cylinders ( 25 MPa, 90-120 litre capacity), and they usually represent about 50% of the gasoline range. As natural gas pipelines do not go everywhere, most conversions are dual-fuel with gasoline. The ignition timing and stoichiometry are significantly different, but good conversions will provide about 85% of the gasoline power over the full operating range, with easy switching between the two fuels . 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 [17,76]. 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 9.5 Why are hydrogen-powered cars not available? The Hindenburg. 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 [73,77]. 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 backfiring. 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 for details about this fuel.
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