Ethanol-laced fuel bad for RX-8?
09-10-2003, 07:10 AM
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Ethanol-laced fuel bad for RX-8?
The federal government has a secret report detailing manufacturer's recommendations on which cars shouldn't use ethanol-laced fuel. The government won't release the report yet. Has Mazda OK'd the RX-8 for ethanol contaminated petrol?
Ethanol is a lousy additive. With basic physical chemistry, you can calculate that the heat of combustion is 33% lower than iso-octane (33kJ/g compared with 44kJ/g). This relates directly to the energy you get from the fuel. This also explains why petrol companies argue that 10% ethanol addition reduces the effective power of the fuel by 3%. By direct proportion, 20% ethanol means a 6% power reduction. Incomplete combustion of ethanol (say on start up) results in acetic acid, which could slowly corrode your motor and exhaust system.
Ethanol is a lousy additive. With basic physical chemistry, you can calculate that the heat of combustion is 33% lower than iso-octane (33kJ/g compared with 44kJ/g). This relates directly to the energy you get from the fuel. This also explains why petrol companies argue that 10% ethanol addition reduces the effective power of the fuel by 3%. By direct proportion, 20% ethanol means a 6% power reduction. Incomplete combustion of ethanol (say on start up) results in acetic acid, which could slowly corrode your motor and exhaust system.
09-10-2003, 12:34 PM
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According to this article in today's "Mercury News", Mazda claims that the RX-8 can run safely on fuel containing up to 10% ethanol. I'd want to hear this from Mazda themselves though.
09-10-2003, 08:07 PM
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Ethanol is a lousy additive. With basic physical chemistry, you can calculate that the heat of combustion is 33% lower than iso-octane (33kJ/g compared with 44kJ/g). This relates directly to the energy you get from the fuel. This also explains why petrol companies argue that 10% ethanol addition reduces the effective power of the fuel by 3%. By direct proportion, 20% ethanol means a 6% power reduction. Incomplete combustion of ethanol (say on start up) results in acetic acid, which could slowly corrode your motor and exhaust system.
I think you answered your own question very accurately.
I would only use fuel containing ethanol, and as little as possible as a percentage, in an emergency situation.
Timbo
09-11-2003, 08:40 AM
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I have read about this issue from the 1960's.
Curtis Wright bought a license for the rotary engine back in 1958 & started there own program.
One of the documented tests they did was octane testing Vs power.
I recall that testing was done from 100 Octane down to 87 Octane with less than a 3% difference in power. No ping or anything like that noted.
Not sure with the compression ratio as I'm struggling to recall what I just wrote. Plus being the 60's, it certainly wasn't turbocharged
Try doing that with a piston engine & watch it go pop!!!!!
So, whilst I will run Optimax in my twin-turbo 20B powered JC Cosmo, I'll use normal unleaded in all my "atmo" rotary vehicles as the only difference will be in the hip pocket.
Curtis Wright bought a license for the rotary engine back in 1958 & started there own program.
One of the documented tests they did was octane testing Vs power.
I recall that testing was done from 100 Octane down to 87 Octane with less than a 3% difference in power. No ping or anything like that noted.
Not sure with the compression ratio as I'm struggling to recall what I just wrote. Plus being the 60's, it certainly wasn't turbocharged
Try doing that with a piston engine & watch it go pop!!!!!
So, whilst I will run Optimax in my twin-turbo 20B powered JC Cosmo, I'll use normal unleaded in all my "atmo" rotary vehicles as the only difference will be in the hip pocket.
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