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Toyota: targeted cooling of upper cylinder liner effective way to improve anti-knock quality and thermal efficiency

Engineers at Toyota Motor Corporation in Japan have determined that cooling the upper part of the cylinder liner on the exhaust side is an effective way to improve anti-knock quality—opening the way to improved engine thermal efficiency. The team presented a paper on their investigation at the recent SAE 2012 World Congress.

In theory, a higher compression ratio and leaner combustion are effective ways to increase the thermal efficiency of an engine; however, higher compression ratios also lead to a higher knock tendency. Thus, the team of Daishi Takahashi, Koichi Nakata and Yasushi Yoshihara noted, it is important to improve an engine’s anti-knock quality. Typical technology approaches for this are reducing the combustion period by utilizing squish, direct fuel injection, and improving engine cooling to lower the temperature of the air-fuel mixture.

Enhancing the engine cooling is very effective for improving knocking. Consequently, engine cooling technologies have been enhanced to improve anti-knock quality over many years. However, excessive improvement of engine cooling means an unnecessary increase in cooling heat loss. To find a good balance between anti-knock improvement and cooling heat loss reduction, this study investigates the effect of temperature of cylinder-head, cylinder-liner, and piston on both knocking and cooling heat loss.

—Takahashi et al.

For the study, the team used computer-aided engineering (CAE) to predict the effects of each part of the engine on engine knocking and cooling heat loss, first calculating the amount of heat energy that the air-fuel mixture receives from the engine cylinder head, liner and piston during the intake stroke. The results showed that the cylinder liner contributes the largest amount of heat energy to the air-fuel mixture, especially on the exhaust side.

They then calculated the amount of heat energy discharged from the combustion gas during the expansion stroke to the head, liner and piston. These results showed that the cylinder liner receives the least amount of energy from the combustion gas.

Overall, the CAE results suggested that cooling the upper part of the cylinder liner on the exhaust side would be an effective way to improve antiknock quality.

The team then used a singe-cylinder engine equipped with a total of 14 independent cooling water paths and about 150 thermocouples to validate the CAE results. Eight of the cooling paths were placed in the cylinder head side, and six cooling paths were placed in the side part of the cylinder liner, on both intake and exhaust sides. Intake and exhaust sides were divided into an upper, middle and lower part. They also switched the material for the cylinder liner from cast iron to aluminum.

Test results showed an agreement with the CAE results, indicating the effectiveness of the targeted cooling of the liner on anti-knock quality.

The current study did not take engine friction into consideration; that effect will be considered in a future study, as well as the application to inline engines.


  • Daishi Takahashi, Koichi Nakata and Yasushi Yoshihara (2012) Engine Thermal Control for Improving the Engine Thermal Efficiency and Anti-Knocking Quality. (SAE 2012-01-0377) doi: 10.4271/2012-01-0377



Interesting and amazing that it was not tried and done many years ago.
Redesigning/increasing the upper cylinder water cooling should not be a huge challenge.


Don't take this report seriously, it is just simple babylike theory scattered by paid employees that had to make a report, probably once a year, to please their boss that himself will forget about it tommorrow. Nobody will change anything except the marketing department that invented recently fad like ecoboost, skyactiv, twin swirl combustion chambers. I worked myself on engine rebuilding and modifications and the exhaust side of the cylinder head on cars and motorcycles is always cooled first then the liquid or air flow reach the intake side after for an even cooling both side, so they rebasched this old theory just because they had to make a report and they didn't know what to talk about so they got old forgotten theory and put it as new.


AD, you are wrong and likely know nothing about real engine research. Toyota R and D produces some of the best and most well respected research in the industry.

Dave R

Makes sense. The upper cylinder liner around the exhaust port is probably the hottest area that unburned air/fuel mixture encounters.

Directing additional cooling there results in lower peak combustion chamber temperatures and thus less risk of engine knock.


This is NOT a new idea.
It is basic, as even they admit; “Enhancing the engine cooling is very effective for improving knocking. Consequently, engine cooling technologies have been enhanced to improve anti-knock quality over many years.”

Next they will “discover” that keeping the exhaust valve cooler is an effective way to improve anti-knock quality and thermal efficiency.

If they have a new method of economically doing any of this (and Toyota probably does), then let’s hear about it.


@ RFH . I know something about real engine research. It work like this, they need to refine the same old engine over and over for publicity and marketing reasons so they got a bunch of paid engineers that will automatically change something for very small increment because they cannot change the fuel that is powering it so the small theoritical increment hover around 0% improvement if we approximate the percentage to the nearest round percentage number. Toyota invested billion in formula one in a period of more then 10 years and they didn't got any victory been beaten by small specialized team and finnally they got out of formula one and now market small conventionnal low output low cost engines for the family and the scrap yard ten year after.


Knock ceases to be an issue with compression-ignition engines.  Combined with supercritical fuel injection, keeping heat in the combustion chamber is an advantage.


A good point EP; just as with Low Temperature Combustion, for some aspects, it's the "wrong way to go".

They have to be sure they get 2 steps forward for one back, not the other way around.


Smokey Yunick understood the cooling/detonation/efficiency/power relationship very well. I knew him, as I lived within a mile of his shop, and I was impressed with his engine knowledge. In fact, his reverse flow cooling system was credited with allowing significantly higher compression on pump gas. This is nothing new.

Spencer Hagenhoff

I believe a Chevy LT1 used this concept(i think they used some sort of steam vents) along with Smokey

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