wvarn1957
Posts: 245
Joined: 7/7/2002
From: Houston,
TX, USA
Status: offline
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The platinum on the glow plug element is a catalyst which initiates the oxidation(combustion) of the fuel. Platinum is a very common component of catalysts used in the petrochemical and refining industries. It will initiate the oxidation of most any organic in the vapor phase. The rate of combustion is dependent on the specific compound, pressure and temperature. Consequently, gasoline can be used, but consistent performance could be problematic.
Because glow fuel is essentially a single component fuel, it works well in IC engines using catalytic combustion initiation. As a result ignition timing will be consistent. Gasoline, on the other hand, is a multi-component fuel and because of EPA's Air Quality regulations is blended for specific areas and for specific seasonal considerations. Consequently the component mix is constantantly changing. In an IC engine which uses spark initiated ignition, this is not a factor in ignition timing. However in an IC engine dependent upon catalytic initiation, the ignition timing is affected by the varation in composition.
There are several ways to minimize this variation in gasoline blends and get somewhat more consistent timing. Using 100 octane low lead Aviation gasoline would be much more consistent than automotive gasoline, since Avgas blends are very consistent from area to area and season to season to season. In additon, using 15% to 20% methanol or ethanol would improve the timing consistency. Other things such as acetone, MEKP, butane or ether would help, but that is getting pretty exotic in mixing techniques and increases the hazard potential of handeling the mixes.
Increasing or decreasing the compression will also affect the ignition timing. Generally lowering the compressing would have the effect of retarding the timing,while increasing the compression would have the effect of advancing the timing.
In addition the idea of varying the tempature of the glow element by varing the amperage will have some effect on the timing, but I wouldn't hazard a guess as to whether or not this would mitigate the impact of the composition variation of gasoline.
I would like to correct a statement that was made in a previous post on the comparison of methanol and gasoline. Methanol, depending on its purity, has a heat content of 8,000 - 9,000 BTU/lb. Ethanol has 11.000-12,000 and typical gasoline blends have 18,000-20-000 BTU/lb. Air to fuel ratios for methanol, ethanol and gasoline are (approximate) 6.5/1, 9/1 and 14.5/1 respectively. An IC engine burning gasoline will run quite a bit hotter than an IC engine burning methanol because of the difference in the latent heats of vaporization.
< Message edited by wvarn1957-RCU -- 11/12/2003 4:05:59 PM >
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