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Old 08-03-2009, 10:46 PM
Location: Texas
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MADISON — Diesel and gasoline fuel sources both bring unique assets and liabilities to powering internal combustion engines. But what if an engine could be programmed to harvest the best properties of both fuel sources at once, on the fly, by blending the fuels within the combustion chamber?
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Old 08-03-2009, 10:48 PM
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Tell me more
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Old 08-04-2009, 10:22 AM
Location: Londonderry, NH
41,492 posts, read 51,367,509 times
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Using Diesel oil as an ignition system in a very high compression Natural Gas reciprocating engine has been done for years. A small amount of Diesel is injected at the proper time into a compressed mixture of Gas and air. The very high compression (around 15:1) heats the mixture enough to light off the oil and the resulting flame lights the gaseous mixture. It allows Nat Gas to be used as a fuel without the danger of a spark ignition in an environment where any leaking gas might be "sparked” into a major explosion. This was a problem with NG pipeline spark ignition engines because pipeline gas is essentially odorless and leaks were hard to detect.

The major difference between Diesel oil and gas (both natural and gasoline) is Diesel oil burns as a droplet from the outside in to nothing with a decreasing heat release during combustion while the gas mixtures burn along a flame front with peak heat release somewhere between ignition and burn out. As the molecular weight of the vaporized mixture increases the susceptibility to detonation is increased. Detonation happens when the gas mixture burns at sonic velocity and created an engine damaging (sometimes destroying) shock wave. Natural gas is a low molecular weight hydrocarbon with only one Carbon atom and is very resistant to detonation. This is why it can be used in Diesel compression ratios.

A reciprocating engine capable of high enough compression to operate on both Diesel Oil and vaporized gasoline in varying mixtures would be very useful where the supplies of either fuel were unreliable.
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Old 08-05-2009, 06:08 PM
Location: Texas
5,070 posts, read 8,983,457 times
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I was just re-reading the article I posted. Looks like the mixture is variable, depending on the load.
Under heavy-load operating conditions for a diesel truck, the fuel mix in Reitz' fueling strategy might be as high as 85 percent gasoline to 15 percent diesel; under lighter loads, the percentage of diesel would increase to a roughly 50-50 mix. Normally this type of blend wouldn't ignite in a diesel engine, because gasoline is less reactive than diesel and burns less easily. But in Reitz' strategy, just the right amount of diesel fuel injections provide the kick-start for ignition.
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