04-26-2015, 10:48 PM
I respectfully disagree about emissions being the primary factor in discontinuing air-cooled engines. A factor - yes, but the real big push for water cooling is because of the desire for more horsepower and larger displacement motors. Gasoline engines are roughly 30% efficient - that means 70% of the energy ends up in heat that has to be transferred away.
Catalytic converters have made it easier to meet emissions standards, but they do reduce power output, which the manufacturers have addressed by increasing displacements and generating more heat energy to radiate away.
As engines make more power, more heat is generated and water cooling is used because the radiators have much larger cooling areas than engine fins. Note that water-cooled engines are also air-cooled. The water simply conducts the heat out to the radiator were it is cooled by air-flow. The coolant does not actually cool anything - it simply conducts the heat away from the engine. In some ways, it works similarly to a home air conditioner that conducts the heat to the outside of the house.
Engines have grown much larger over the last 40 years. A 650 used to be a big bike. Now, even so-called adventure bikes are 1200cc or bigger. More displacement equals more heat to radiate to the air.
Water cooling has a second advantage in that the coolant reduces noise radiated by the engine. Fins tend to radiate noise and motorcycle must meet noise standards.
There are more efficient methods of moving heat to radiators than water but they are expensive and somewhat caustic. Communications satellites use heat-pipes, which use chemicals like ammonia to move heat from electronics to radiators. The ammonia is liquid when cold and vapor when hot and is much more efficient than water or anti-freeze.
I still think air-cooled engines have a future, especially in smaller engines.
Catalytic converters have made it easier to meet emissions standards, but they do reduce power output, which the manufacturers have addressed by increasing displacements and generating more heat energy to radiate away.
As engines make more power, more heat is generated and water cooling is used because the radiators have much larger cooling areas than engine fins. Note that water-cooled engines are also air-cooled. The water simply conducts the heat out to the radiator were it is cooled by air-flow. The coolant does not actually cool anything - it simply conducts the heat away from the engine. In some ways, it works similarly to a home air conditioner that conducts the heat to the outside of the house.
Engines have grown much larger over the last 40 years. A 650 used to be a big bike. Now, even so-called adventure bikes are 1200cc or bigger. More displacement equals more heat to radiate to the air.
Water cooling has a second advantage in that the coolant reduces noise radiated by the engine. Fins tend to radiate noise and motorcycle must meet noise standards.
There are more efficient methods of moving heat to radiators than water but they are expensive and somewhat caustic. Communications satellites use heat-pipes, which use chemicals like ammonia to move heat from electronics to radiators. The ammonia is liquid when cold and vapor when hot and is much more efficient than water or anti-freeze.
I still think air-cooled engines have a future, especially in smaller engines.