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Discussion Starter #1
Hi Guys and Girls,

As a new Mazda 6 owner (tomorrow) I thought I would do a little research into the premium and hi-octane premium fuel topic.

Being a Qantas pilot and technically minded, I have been studying numerous university and industrial studies in order to determine the right fuel for the EMS (engine management system).

Two interesting points were found (and I stand corrected if you are better informed)

1. The 2.3 litre engine only has one "knock" (cylinder 2) sensor rather than individual sensors for each cyclinder. This leaves the other cylinders unprotected should conditions prevail that bring the onset of detonation.

Having a compression ratio of 10:6.1 and trying to run normal unleaded, regardless of the "knock sensor" is just tempting fate.

The engine ignition module appears to have a maximum predetermined ignition advance curve. Using 98 octane fuel, will not provide additional power over 95-96 octane fuel. But they do have additional detergents and additives which will keep your fuel system clean and operating at the top of its design perimeter.

12/05/03: This has now been confirmed by Mazda Japan.

The discussion about 98 octane fuel being more dense is correct. But one factor is missing in this discussion - density also is related to temperature and air density must also be considered. The higher the temperature the less the air density. Just food for thought ....

2. Why is Shell Optimax banned for sale in Western Australia and South Australia ?
Because it doesn't meet the state government quality standards. The Benzene content is too high .... try doing a little research into the corrosive properties of this additive.

I'm going to use BP products and will probably elect to use BP Ultimate just to keep the fuel system at its optimum. I have a contact at BP Australia - Mathew Hamilton if you have any questions [email protected]

Please let me know what stories you have heard relating to these topics.

Warren
 

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Reading Topic: Caution: Shell Optimax

Thanks for the information WRW!

however, i would like to clarify one thing u said in your discussion. You said "The higher the temperature the less the density"...as a physics student, that sounds incorrect. Isnt temperature and density directly related, as density is also related to pressure, therefore, higher pressure leads to a higher temperature? As temperature is a measure of the average kinetic energy of the particles, then wouldn't 'compressing', making denser, the fuel increase its temperature?
 

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Replying to Topic 'Caution: Shell Optimax'

Hi Alexchu and other guys and girls,

Alex, I hope you received my message and it explains my views in a more technically explained way, that most people wouldn't understand. I look forward to further discussing this with you and listening to your views.
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For everybody else, it is my understanding, that an electronically controlled, fuel injected, fixed compression ratio, normally aspirated internal combustion engine operates as following at sea level at a fixed temperature for both air and fuel.

The correct fuel/air ratio for best power is in the vicinity of 15:1 (15 parts air for 1 part fuel). This is achieved by computations in the Engine Management System.

The engine controls the amount of fuel injected, by keeping the injection fuel rail at a constant pressure and the amount injected is controlled by the time the injection nozzle is open and closed. There is no measurement of fuel density (the EMS doesn't know if your using normal unleaded, premium or high octane fuel) . Or is fuel temperature monitored by the EMS.

The amount of air entering the engine is controlled by the throttle body that measures air density by comparing air pressure and air temperature.

There is not direct measurement of combustion temperature though there is an EGT (exhaust gas temperature sensor) which provides information to the EMS more for emission standards than that of performance. But logic must conclude that the EGT figures must be used by the EMS to calculate the fuel/air ratio.

I can't clearly understand how the fuel density plays a role in this instance.

The only possibility I can see, but don't fully understand, is that the fixed fuel pressure on the fuel injection rail, can be maintained with less fuel only if high density fuel is used.

What is everybody else's view on this ?

Warren
 
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