Anything else whatsoever... Keep it clean though.
#20536
Oldsmobile Designed a 12-1 compression engine before the last war, known as a Kettering engine. It would have been more powerful than current V8's which were typically 7 to1, in fact a V6 would have been more powerful and lasted longer than many V8's built at that time.
https://books.google.co.uk/books?id=YyQ ... e&q&f=true Now as the war happened so I can't say for definite whether it was stopped by the car builders, the oil industry or the war. At time just after the depression a car that did 25 more miles in city traffic out if the same tank of fuel would have been quite a selling point. For the gasoline to be that high octane it would have needed a lot more lead though.
Last edited by Yachtsman on Wed Aug 09, 2017 8:49 pm, edited 1 time in total.
#20549
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).

Image

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.

Image
#20552
Macs wrote: Wed Aug 09, 2017 4:00 pm Very interesting article. It looks like they're rediscovering some of the old lessons from the sixties.
Pretty much, only with the addition of modern CAD and computer controlled engines.

Mazda's goal was to have the cheapest engine possible that could still compete on the MPG and emission front. That meant no turbos or hybrids. So they had to throw every naturally aspirated trick of the book at it: high compression, long tube headers, slightly oversquare that is consistent over different displacements, and a clever ECU. Most other companies either went with the hybrid or turbo'd undersized engine route, which are other clever solutions with their own set of benefits and detriments.

But Yachtsman thinks that he is alone in thinking about high compression even though engineers far better than him have already done the work and have gone from CAD drawings to hundreds of thousands of engines a year production. I look forward to the next gen spark assisted HCCI engines Mazda is teasing us with. I'll probably be able to buy one off the showroom floor before Yachtsman gets his boat anchor of an engine running.
#20554
Many engines today run 12:1 on pump gas. My old tech X5 runs 10.5:1 on regular gas, not premium. And, as several others have pointed out (and even given you examples), lots of flex fuel vehicles run up to 16:1, and run on everything from regular gas to E85.

You simply chose to ignore that others have already done what you want to do and still haven't seen the 'small molecule-high compression' effect you postulate.
Last edited by apollard on Wed Aug 09, 2017 5:36 pm, edited 1 time in total.
#20555
We do use higher compression, as one of many efficiency improvements. To tag onto infinityedge's first post, the answers include standardization, and combustion control among others. Since WWII when all high-octane fuels were used for war and everything else had to run on "MoGas" of about 68 octane; standardized octane at fuel stations has gradually increased along with the technology to burn it efficiently. With governmental standardizations, your typical grades of gasoline/petrol were established, and that's what we're using. To get best fuel economy, may cars now require higher standardized octane (98 RON or 92 RON/MON). But to go much higher requires greater cost in creating that compression long-term, much as diesel engines are considerably more expensive to handle it.

The combustion control is a primary factor (no matter the fuel), as it is what allows or denies the use of a certain fuel, and efficiency gained under specific conditions. Technology has improved in combustion control to allow higher compression and greater energy conversion. It's how you control the burn that makes your final efficiency numbers. So, increasing from 10:1 to 15:1 gains (in that example) 9%, but other efficiency technologies can combine to increase it far more. Average auto engine efficiency has nearly doubled, with the same octane, over the last 25 years. That's a lot more than 9%. Unfortunately, both the mass of cars (bigger, impact safety, airbags, lane change sensors, cameras, AC, etc.) and other limitations like emissions requirements keep MPG gains limited. For example, the '08 Honda Civic goes no further on a gallon of gas than the '88 Cadillac DeVille :shock: 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.

Considering all the areas that efficiency can be improved; using compression falls from favor. Consider just the 'costs' in using it, such as the reduced lifespan — or costs to restore lifespan — from working the engine 29% harder with a 10 to 15:1 jump in squeezing that air tighter every time. More wear, increased structural rigidity, greater requirements for ring sealing, and other costs just to reach that 9% perfect scenario. Flex Fuel engines are approaching 20:1 in current designs adding yet more costs to enable that capability. Adding $1000 to the cost of a car's technology is the equivalent to a full year of average fuel cost. There is a balance that the market requires.

David
#20556
PSIG wrote: Wed Aug 09, 2017 5:32 pm Consider just the 'costs' in using it, such as the reduced lifespan — or costs to restore lifespan — from working the engine 29% harder with a 10 to 15:1 jump in squeezing that air tighter every time. More wear, increased structural rigidity, greater requirements for ring sealing, and other costs just to reach that 9% perfect scenario.
The really funny thing is he chose ford 200 L6 pistons or is build, they are not known for their toughness, and get replaced with custom forged parts in most performance 200 builds.
#20557
infinityedge wrote: Wed Aug 09, 2017 3:12 pm 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).

Image

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.

Image
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 run at 14 to 1 too. As no mention of Knocking is made in that report perhaps the Oldsmobile engineers cured it perhaps the cured of loss of torque too or is that a symptom of using gasoline at high compression. Does Methane, or Methanol, propane or butane have the same problem.
Last edited by Yachtsman on Wed Aug 09, 2017 8:00 pm, edited 1 time in total.

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