[infinityedge]

The skyacti-g is indeed 14 to 1, but is made of aluminium I'm sure if the Kettering had able to be made of aluminium it would have been able to runat 14 to 1 too

They never got a production engine higher than 10.75:1.

That aside, how the hell would aluminium construction had any influence on compression ratio?

Do you ever think through your comments before posting them or is this just a stream of consciousness exercise?

[RichCreations]

The skyacti-g is indeed 14 to 1, but is made of aluminium I'm sure if the Kettering had able to be made of aluminium it would have been able to runat 14 to 1 too

They never got a production engine higher than 10.75:1.

That aside, how the hell would aluminium construction had any influence on compression ratio?

Do you ever think through your comments before posting them or is this just a stream of consciousness exercise?

I hate to in anyway hint he is partially right (he is not) but in general aluminum heads allow for a a slightly higher compression ratio then cast iron, due to better thermal conductivity (less hot spots) all other things being equal...

[infinityedge]

Perhaps, but when Olds switched to an all aluminum design, they decreased compression.

[Yachtsman]

As has been pointed out to you many times before:

http://www.mazda.com/en/innovation/tech ... kyactiv-g/

Increasing the compression ratio considerably improves thermal efficiency. The compression ratio of recent gas engines is generally around 10:1 to 12:1.

Theoretically, if the compression ratio is raised from 10:1 to 15:1, the thermal efficiency will improve by roughly 9%. However, one of the reasons preventing the spread of high compression ratio gas engines is the large torque drop due to knocking (Fig.1).



Knocking is abnormal combustion in which the air-fuel mixture ignites prematurely due to exposure to high temperature and pressure, creating an unwanted high-frequency noise. When the compression ratio is increased, the temperature at compression top dead center (TDC) also rises, increasing the probability of knocking.

In order to lower the temperature at compression TDC, reducing the amount of hot exhaust gas remaining inside the combustion chamber is effective. For example, with a compression ratio of 10:1, a residual gas temperature of 750 deg. C, and an intake air temperature of 25 deg. C, if 10% of the exhaust gas remains, the temperature inside the cylinder before compression increases by roughly 70 deg. C, and the temperature at compression TDC is calculated to increase by roughly 160 deg. C. Therefore, it can be easily inferred that the amount of residual gas has an major impact on knocking.

These calculations are summarized in Fig.2, and as indicated, if the amount of residual gas is halved from 8% to 4%, the temperature at compression TDC is calculated to remain the same even when the compression ratio is increased from 11:1 to 14:1.

This reduction of residual gas was focused on for SKYACTIV-G, enabling the realization of a high compression ratio gasoline engine.

You're forgetting the fuel isn't Gasoline it's Ethanol or Methane or Methanol it's some other fuel so none of those graphs apply

[Yachtsman]

As has been pointed out to you many times before:

http://www.mazda.com/en/innovation/tech ... kyactiv-g/

Increasing the compression ratio considerably improves thermal efficiency. The compression ratio of recent gas engines is generally around 10:1 to 12:1.

Theoretically, if the compression ratio is raised from 10:1 to 15:1, the thermal efficiency will improve by roughly 9%. However, one of the reasons preventing the spread of high compression ratio gas engines is the large torque drop due to knocking (Fig.1).



Knocking is abnormal combustion in which the air-fuel mixture ignites prematurely due to exposure to high temperature and pressure, creating an unwanted high-frequency noise. When the compression ratio is increased, the temperature at compression top dead center (TDC) also rises, increasing the probability of knocking.

In order to lower the temperature at compression TDC, reducing the amount of hot exhaust gas remaining inside the combustion chamber is effective. For example, with a compression ratio of 10:1, a residual gas temperature of 750 deg. C, and an intake air temperature of 25 deg. C, if 10% of the exhaust gas remains, the temperature inside the cylinder before compression increases by roughly 70 deg. C, and the temperature at compression TDC is calculated to increase by roughly 160 deg. C. Therefore, it can be easily inferred that the amount of residual gas has an major impact on knocking.

These calculations are summarized in Fig.2, and as indicated, if the amount of residual gas is halved from 8% to 4%, the temperature at compression TDC is calculated to remain the same even when the compression ratio is increased from 11:1 to 14:1.

This reduction of residual gas was focused on for SKYACTIV-G, enabling the realization of a high compression ratio gasoline engine.

The compression of recent petrol/Gasoline engines has been as high as 12 to1, but that's only because they're made of aluminium.

[infinityedge]

If aluminum is so important, why did you use an iron block with iron heads?

[Yachtsman]

If aluminum is so important, why did you use an iron block with iron heads?

I used what Ford (UK) Built, I deemed a block strengthened to use diesel was more important and increasing the compression was what this build is all about.

[infinityedge]

If increasing compression was what this build is all about and aluminum allows you a greater increase compression, why didn't you use an engine that was aluminum, or at least one with an aluminum head?

[PSIG]

Here we go off the tracks again. Aluminum is relatively irrelevant, and in the real world allows perhaps 0.5:1 additional compression, but at the same time by absorbing the heat more readily it reduces the engine output slightly. It's a draw and does not have bearing to what you're seeking. Again, engines (iron or Al) have been produced for public use, with standardized "pump gas" at compressions higher than 12:1 for over 50 years.

This sends us back to the different "compressions" and how they are used. A 7:1 and a 12:1 engine can both be manipulated to run the same fuel without detonation, as the effective compression (not just static or dynamic) can be altered. This is one of the factors that allow the 18:1 Flex engines to run 87 octane gasoline without detonation, and how the "HiPo" engines of the muscle cars could run factory 11:1+ on pump gas. Yachtsman, all the talk of static compression ratios is not of much value until you read and understand some of how it actually applies.

David

[sinfab]

For example, the '08 Honda Civic goes no further on a gallon of gas than the '88 Cadillac DeVille and needs 'Premium' octane fuel to do it. It actually costs more to drive that Civic than an older V8 Cadillac from A to B.

Just curious what this is based on? A quick google has the Caddy at 15 city/22 highway, and even the "high performance" Civic Si from 2008 is 21 city/29 hwy. The base '08 civic gets 26 city/34 highway. The Si needs premium, while the base uses regular.
The base civic has a 140hp, 1.8L inline 4. The DeVille has a 155hp 4.5L V8. The Si has a 197hp 2.0L inline 4.