Speed JUnkyz
January 19th, 2010, 08:43 AM
About different automotive fuels...
Diesel, has a slightly higher calorific value (about 16,000 Calories per LB of fuel) than Petrol does. But it has a very low Octane rating, meaning it "self ignites" due to heat or rather it has a low Self Ignition Temperature (SIT). This low octane makes it useless in a petrol engine! It would pre ignite, detonate uncontrollably, and because it has a higher evaporation temperature may not fire easily with a spark plug!
Even a small amount added to a petrol engine causes it to "knock, ping, pink, or whatever! Diesel (and kerosene, paraffin) is good in a diesel engine precisely BECAUSE it ignites spontaneously when its hot! The heat of compression alone ignites the fuel as it is fired into the cylinder. Petrol is designed NOT to ignite until it sees a source of ignition, the spark.
http://www.tuning.wanadoo.co.uk/images/fuels.1.jpgPump Petrol has a slightly lower calorific value (14,700 15,400 calories per LB of fuel) but it has a much higher anti auto ignition temperature & knock, or detonation temperature. In other words a diesel engine would not fire! It NEEDS a spark for ignition. That is until you increase the temperature or boost level, in the cylinder!!! And then we get detonation problems. Detonation is when the fuel spontaneously explodes rather than smoothly burning. It destroys engines very fast! So we need higher Octane fuels for really high compression use, or high boost levels with a turbo etc.
Race fuel, C14, C16 etc These are the same as pump fuel but much higher Octane. Used in a car that does not need this extra octane it is simply a waste of money. To see more power you need to take advantage of the new higher detonation limit! By increasing boost, or by increasing compression ratio.
Methanol is a "cold" or "cooling" fuel, that is basically alcohol. It is VERY high octane so really high compression ration can be used. Because it has only 7,000 approx calories per LB 2.2 to 2.4 times as much is needed at any one time! This means HUGE fuel jets are needed, and a corrosion proof fuel system, You cannot just run your engine on it! If used in a similar motor to a petrol one no extra power will be available. But it again allows higher compression ratios, or more boost! So in this case more power can be realised.
Nitromethane is not really a fuel, on its own but almost is! It is however an oxygen producer! As we already know, oxygen allows fuel to be burned! This stuff is a way of getting more oxygen into your engine! But its £50 per gallon price, and the fact that it makes all kinds of nasty acids that turn your oil to milky water in ten mins flat mean race use only! It is used mixed with methanol normally as its fuel. Although its almost a monopropellant, engines breath air, so "some" fuel has to be added. It is added to methanol base fuel, and can be used in 5 percent up to high 90's percentages! Obviously the more Nitromethane that is added to the fuel the more oxygen you have added. So you then need more fuel! So you go in ever decreasing circles as the percentage rises until you simply cannot feed it enough fuel! Strange stuff. Works though. Top Fuel dragsters make 5,000 bhp! Go from 0 to 300 mph in 4 seconds. From low tech pushrod V8 engines... A similar effect could be had by adding oxygen via a Nitrous Oxide Injection System.
Diesel, has a slightly higher calorific value (about 16,000 Calories per LB of fuel) than Petrol does. But it has a very low Octane rating, meaning it "self ignites" due to heat or rather it has a low Self Ignition Temperature (SIT). This low octane makes it useless in a petrol engine! It would pre ignite, detonate uncontrollably, and because it has a higher evaporation temperature may not fire easily with a spark plug!
Even a small amount added to a petrol engine causes it to "knock, ping, pink, or whatever! Diesel (and kerosene, paraffin) is good in a diesel engine precisely BECAUSE it ignites spontaneously when its hot! The heat of compression alone ignites the fuel as it is fired into the cylinder. Petrol is designed NOT to ignite until it sees a source of ignition, the spark.
http://www.tuning.wanadoo.co.uk/images/fuels.1.jpgPump Petrol has a slightly lower calorific value (14,700 15,400 calories per LB of fuel) but it has a much higher anti auto ignition temperature & knock, or detonation temperature. In other words a diesel engine would not fire! It NEEDS a spark for ignition. That is until you increase the temperature or boost level, in the cylinder!!! And then we get detonation problems. Detonation is when the fuel spontaneously explodes rather than smoothly burning. It destroys engines very fast! So we need higher Octane fuels for really high compression use, or high boost levels with a turbo etc.
Race fuel, C14, C16 etc These are the same as pump fuel but much higher Octane. Used in a car that does not need this extra octane it is simply a waste of money. To see more power you need to take advantage of the new higher detonation limit! By increasing boost, or by increasing compression ratio.
Methanol is a "cold" or "cooling" fuel, that is basically alcohol. It is VERY high octane so really high compression ration can be used. Because it has only 7,000 approx calories per LB 2.2 to 2.4 times as much is needed at any one time! This means HUGE fuel jets are needed, and a corrosion proof fuel system, You cannot just run your engine on it! If used in a similar motor to a petrol one no extra power will be available. But it again allows higher compression ratios, or more boost! So in this case more power can be realised.
Nitromethane is not really a fuel, on its own but almost is! It is however an oxygen producer! As we already know, oxygen allows fuel to be burned! This stuff is a way of getting more oxygen into your engine! But its £50 per gallon price, and the fact that it makes all kinds of nasty acids that turn your oil to milky water in ten mins flat mean race use only! It is used mixed with methanol normally as its fuel. Although its almost a monopropellant, engines breath air, so "some" fuel has to be added. It is added to methanol base fuel, and can be used in 5 percent up to high 90's percentages! Obviously the more Nitromethane that is added to the fuel the more oxygen you have added. So you then need more fuel! So you go in ever decreasing circles as the percentage rises until you simply cannot feed it enough fuel! Strange stuff. Works though. Top Fuel dragsters make 5,000 bhp! Go from 0 to 300 mph in 4 seconds. From low tech pushrod V8 engines... A similar effect could be had by adding oxygen via a Nitrous Oxide Injection System.