Why is water cooled better for EPA emissions purposes? Is it because the higher temps produce more complete combustion? or what?

Higher engine temps produce oxides of Nitrogen during combustion, which is a greenhouse gas.

 

Thanks guys
I now have one heck of a headache

 

My understanding of epa regulations is they want to know that any given vehicle, will emit a given amount of measurable pollutants over the life of the vehicle. So by regulating the temp cars or bikes run at, they can predict how much. With a air cooled motor it doesn't run at a constant temperature like a vehicle with a thermostat. On a cool day it requires more fuel to run good, but when the temps go up the fuel required also changes.The amount of tailpipe emissions does not remain constant or predictable. It seems like Harley has been able to meet the specs for pollutants allowed by their use of fuel injection.Soon as the epa numbers change, they won't be able to meet them with fi itself and will have to go to water cooling to keep producing bikes. Kawasaki went to water cooling a few years back and is able to build a 2000cc motor that make 145 ft pound of torque and 125 hp. Power can be made with water cooling but it will be the end of an era.,,

 

You might want to read the original question. He asked why liquid cooling was a more efficient design, not whether a current HD motor would be better if it were liquid cooled.

 

Higher compression without pinging

 

Heat is energy and the more you can control the unused energy the more horsepower you can attain from the same build and it isn't just water. Using friction free ceramic bearings can reduce heat which transfer into a horsepower gain. Why does an all aluminum engine produce more horsepower than a cast iron motor that is built as identical as possible? Heat, which is far more controllable in the aluminum engine than it is the cast engine.

 

As mentioned earlier a water cooled engine runs at a more steady temp therefore a more uniform combustion which results in less emissions.

I believe the unburned gasses or oxide issue was addressed by engineers by adding a catalyst in the exhaust system on 07 or 08 and later models.

 

Many of the posters have answered the basic questions, but to fully discuss how a liquid cooled engine can generate more power than an air cooled engine would take several textbooks worth of writing. My field of expertise has been in designing rotating machinery such as turbines and compressors, but the physics are the same. First of all, using water or some other liquid coolant does not enable the engine to run faster or to have more power. What is does do it define the operating environment. What did he say?

I could build an air-cooled V-Twin motor that had the same power as any other bike engine out there (with many modifications of course) but the environment required to keep it cool through the use of air alone is not available and not consistent. The bike could only be ridden at specific outside temperatures, at qualified speeds, and with Venturi tubes directing huge amounts of air at specific points. The air-cooled engine is dependent on the surrounding environment, the speed you are traveling, the ambient temperature and wind, the oil viscosity, the bike's aerodynamic design, and on and on for its cooling. Everyone of these that is outside the bike fluctuates and so the design has to account for extremes on each end of the scale.

On a liquid cooled engine, the cooling process is controlled, consistent, and can be located at the critical points not just on the exterior of the motor. The engine designer knows the coolant material specifications, the inlet temperature of the coolant and the outlet temperature of the coolant and can therefore calculate the thermal expansion and operating temperature of every part in the engine within reasonable expectations. Remember, heat is not only generated through the combustion process in the cylinders, but also at every friction point as parts move. You may not realize the extreme pressure (heat generation) that exists in a simple bearing when you have a shaft rotating on a film of oil at several thousand rpms...it can be in the hundreds of thousands psi with several hundreds of degrees temperature rise. Knowing the various amounts of thermal expansion that will exist, the engineer can start reducing clearances (what most mean when they say tolerances) between the engine parts which in turn increases engine efficiency. Beyond the clearance reduction due to known thermal expansion, with a controlled thermal environment the engineer can now start using some of today's thermoplastics which perform much better and allow much closer clearances than their steel counterparts. As an example I worked with Amoco Oil in the development of a thermoplastic named Torlon which has the coefficient of friction less than that of oil but it can only be used at specific temperatures due to its very high rate of thermal expansion.

Once the cooling process is under control and the efficiency of the engine is raised to to a certain level, then and only then does it makes since to start redesigning other aspects of the engine to improve power output. It makes no sense to incorporate advanced cylinder head design and stratified charge systems to improve the combustion efficiency if all your gains will just blow by the rings. Only when the sealing effects of the rings have been improved, or the eventual elimination of the rings through the use of thermoplastics, can the benefits of increased combustion be fully realized.

Many other aspects that other members have mentioned such as air/fuel mixtures,timing, etc play into this whole process as well but it all starts with the ability to define the operating environment more closely in a liquid cooled system than in an air-cooled system.

 

Water cooling allows more heat to be removed from the cylinder and head.
A cooler head means less detonation (pinging) risk and thus more ignition advance and more efficient engine with higher specific power.
Less problems with termal expansion and so on.
Liquid cooling is simply better, more efficient and keeps a more stable engine temp.
Air cooling is way simpler, more reliabile and cheaper.
For example, WW II fighters operating in Europe, with ready, short supply lines and an abundance of ground where to land in case of a problem used water cooled engines.
American fighters in the Pacific theater, where one might have to fly for hours before coming back to his carrier or airfield used air cooled engines.
A water cooled engine aircraft could be shot down by a well placed rifle shot (as happened to some P-51 Mustang with their vulnerable ventral radiator) while an F6F or F4U could fly its pilot home with two blown cylinders without much effort.

 

I agree with most of your statement. Liquid cooling allows a more constant environment for motors to operate in, so their state of tune allows for more consistent power output. Water cooling in a plane is not practical. When you have unlimited cool air at your disposal. And planes don't have to deal with stop and go traffic for hours.You would hate it if your radiator sprung a leak over the Atlantic.lol. I think the big issue with Harley is that no one whats to see a big honkin radiator in front of their bike that was never there before. But if you can get more constant horse power out of it in all running conditions, without pinging and all other heat related issues, people will eventually warm up to the idea.The purists will hold onto the air cooled but alot will go for the new technology.Just about every motor builder there is uses water to cool the motors so there must be something to it.,,