| Author | Message | ||
     Swordsman |
FIRST, let me say that I have no opinion one way or the other on whether or not Buell should develop a water cooled engine. ALSO, I'm not asking for opinions on why you feel Buell should or should not develop this controversial chunk of machinery. My question is: what is the attraction of a water-cooled engine? Does it somehow allow more horsepower? Better torque? No more noisy fan? Seems like it's need has been debated a countless number of times, yet I've never heard exactly why some people want it... only that it's THE magic bullet that will make Buell more competitive with other bikes.  Seriously though, what is it about water-cooled? Can anyone explain the technical reasons? I tried looking this up in the Search, but it could take a month to sort through all the debates!  Thanks, ~SM | ||
| Gentleman_jon |
Simply put, as specific output per cubic inch of displacement rises, the engine generates more and more heat. At a certain point, air cooling can no longer cool the motor adequately, and the engine overheats. Overheating causes the engine to fail, often by seizing. Water cooling provides a way to remove more heat from the engine by using a radiator to exchange heat with the atmosphere more effectively than can be done by the engine fins alone. Other benefits of water cooling are reduced mechanical noise, and more controlled thermal expansion of the engine and related parts. Got it?  | ||
| Ducxl |
+1 The gent just answered it very accurately.Let's please not start debating/arguing this yet again...Stop it here. | ||
| Brineusaf |
The long version Advantages and disadvantages Cooling, however, is also limited by energy (heat) density. A small, very hot component is difficult to air cool because air has low heat density. If the air speed is low, then there is only a small mass of air to carry away heat. Since there is little mass, the air which is cooling the part gets nearly as hot as the part, and then the temperature difference is small so cooling is poor. Blowing more air over the part improves cooling, but blowing air fast creates noise and uses power. (Doubling the air speed may take eight times the power). In contrast, liquids have much higher heat density and so a comparative trickle of liquid can keep the part cool. A major reason that heat density is important is that the most significant cause of engine failure in modern engines is hot spots. The engine as a whole may be cool enough, but if one part of the engine overheats, the engine eats itself. Slight overheating makes the engine wear out faster and gross overheating causes the engine parts to fail quickly. Common hot spots include parts of the cylinder head, exhaust valves, pistons, and cylinders. Unfortunately, many hot spots are small and located where it is difficult to blow sufficient air over them. Furthermore, engine materials are not perfectly conductive, so it is often not possible to "cool at a distance" by building a metal bridge to a place where it is easy to blow a lot of air. Liquid-cooling is thus a good solution to a difficult problem, but sometimes it is even difficult to move enough liquid coolant to keep a part cool. When liquid coolant gets to an engine hot spot, it may boil, expand to a gas, and momentarily stop the flow of coolant over the hot spot -- which then becomes even hotter. When more coolant reaches the hot spot, it simply boils. The gas bubbles may disappear again as they mix with newly circulated coolant, and the hot spots may be damaged by localized boiling even though the radiator contents are not unusually hot. Indeed, the engine temperature sensor may indicate the engine is running cool overall, even though one part is dangerously overheated. Waterless coolants, PG or PG/EG, are good at avoiding hot spots because of their very high boiling point of 370F and that they don't expand as much as water when vaporized. Water vapor takes up 60 times more space than waterless coolant vapor. In an air-cooled engine, the coolant is already a gas and thus cannot boil. Thus, while air-cooling makes it harder to avoid hot spots, air-cooling also tends to limit sudden hot spot problems caused by boiling coolant. Using air-cooling eliminates an entire engine subsystem and at the same time eliminates problems with coolant freezing. It simplifies engine design and can lead to markedly better engine reliability, though the benefits of reduced complexity must be traded against reliability problems caused by worse thermal control. Using air-cooling also eliminates the coolant radiator and the weight of multi-wall engine parts needed to capture the coolant without leaks. Air-cooled engines are thus often lighter per unit power than liquid-cooled engines. However, cooling fins on an air-cooled engine can be expensive to make compared to liquid-cooled engines, even though liquid-cooled engines require tricky hollow construction. The liquid in a liquid-cooled engine also serves as sound insulation. An air-cooled engine must ensure good passage of air over the engine and thus it is difficult to substitute some other kind of sound deadening. In addition, using air to cool small hot parts means air must flow faster than for the radiator of a liquid-cooled engine, even though the air-cooled engine has much greater temperature differences to aid cooling. For both of these reasons, liquid-cooled engines are typically quieter for a given power output. Liquid-cooling makes it easier to maintain each part of the engine at a given temperature in normal operation. Air-cooled engines can have the hot-spot problems described above, and getting enough air to the hot spots may cause other parts of the engine to run too cold. Liquids have less temperature rise as they absorb waste heat. Thus, the coolant temperature varies less with engine load. In turn, more even temperature of liquid-cooling means better component tolerances can be maintained, which can improve both durability and emissions. It may be possible to achieve good temperature control with an air-cooled engine, but at the expense of more complicated thermal management and increased weight. Similarly, peak power from a given displacement of air-cooled engine is typically limited compared to water-cooled counterparts, so liquid-cooled engines may be heavier but also fit in a smaller space. | ||
| Brineusaf |
Also... Difficult to generalise For all these reasons, it is difficult to make generalisations about air-cooled or liquid-cooled engines. Air-cooled Volkswagen kombis are known for sometimes "eating engines", with both rapid wear in normal use and sometimes sudden failure when driven in hot weather. On the other hand, air-cooled Deutz diesel engines are known for reliability even in extreme heat, and are often used in situations where the engine runs unattended for months at a time. It is usually more difficult to get either low emissions or low noise from an air-cooled engine, two reasons why most road vehicles use liquid-cooled engines. It is also often difficult to build large air-cooled engines, so nearly all air-cooled engines are under 500 kW, whereas large liquid-cooled engines exceed 80 MW (Wärtsilä-Sulzer RTA96-C 14-cylinder diesel). A reliable generalisation is that for a given power level it is more difficult to build a light liquid-cooled engine. Weight is one reason air-cooling is common in aircraft engines, though reliability through simplicity and ready access to cool air are two other reasons. | ||
| Swordsman |
WOW Brine, I think you covered it. That certainly answers my question, and also explains why there has been no definitive answer to the ongoing "should they build it" debate. Thanks a bunch! Now, QUICK, someone lock this thread before there's an argument!  ~SM (Message edited by Swordsman on January 29, 2007) | ||
| Brineusaf |
Indeed, have a nice day! | ||
| Nutsnbolt |
No kidding. I can just feel Rocket getting ready to flame somebody up. | ||
| Ft_bstrd |
You are sucking my will to live! | ||
| Spatten1 |
Great write up Brine. I'd also consider that with liquid cooling an engine stays in a relatively narrow operating temperature range. This means less expansion/contraction at widely varying running conditions. The result is tighter tolerances during operation over a range of conditions. | ||
| Svmotoman |
Is there any exotic cooling techniques that an innovator like Erik Buell should/could be considering? We have a lot of engineers on this board, lets hear from them.... be creative. | ||
| Ducxl |
Excellent job there Brine,very accurate.I was just pointing out where we've debated/argued this to death.There're "proponents" and "opponents" in a dichotomous battle. I'm ALL for water,but everyone knows that.. | ||
| Jlnance |
Seriously though, what is it about water-cooled? Can anyone explain the technical reasons? You've got some great answers, but I'd like to add something. Water cooling has allowed more powerful engines to be built. I've asked the question before, "what if someone managed to build a sufficiently powerful air cooled engine. Would that make you happy?" From what I can gather, the answer is no. There are people who want a water cooled engine just because. | ||
| Skully |
Good points all of you. Please remember that Cycle World (I think) named the Ducati DS1000 air cooled motor as the best street bike motor in the world. So is it really an issue with air cooling, perceived technology, or power? | ||
| Ducxl |
BELIEVE ME when i say,i'd take an aircooled engine ANY DAY over a watercooled engine.Provided it could make over 120 RWHP AND not be a grenade motor. But physics prevent it in a sport motorcycle. | ||
| 45_degrees |
You are wrong Duc. The 993 911 was air-cooled and making a lot of power and it was enclosed and and tucked away in the back of the car. It could even handle the extra heat of turbocharging. I don't think they were grenade motors. The RR isn't a grenade motor. It can survive brutal endurance racing. A version of that tuned for the street would be very reliable. The RR engine is ENGINEERED to make a lot of power reliably... 1338 cubic centimeters... XB13. | ||
| Spatten1 |
Water cooling has allowed more powerful engines to be built. I've asked the question before, "what if someone managed to build a sufficiently powerful air cooled engine. Would that make you happy?" I don't think anyone wants liquid cooling just to have the technology, I think it is the results people are after. The "if someone managed" part is where the problem lies. In the automotive world there is a lot of money spent every year on engine development, and if reliable power was available in a light, small, aircooled package, it would be out there. Air cooled engines just seem to have a power limitation if you need to focus on engine size and weight in addition to power. Also, as said above, the water jacket dampens noise. You can have more exhaust noise with a more free flowing exhaust if you get rid of the engine noise, and still meet federal regs. | ||
| Spatten1 |
45 degrees: Then why did Porche change to liquid cooled engines? They must have had a good reason to re-tool and re-design. Also, the RR does not meet noise or exhaust emissions, and we have no idea if it is reliable enough to be a street engine. it is all supposition until one gets 30k on the road. | ||
| 45_degrees |
Svmoto... An idea I have off the top of my head (I am not an engineer) that may work, but I'm not saying it would nor am I saying liquid-cooling is necessary, is to make a NO MOVING PARTS liquid-cooling system using methanol. Some computers use this type of system for cooling. Methanol is a fairly cold liquid and it flows in the permanently sealed systems by convection. However, our bikes are also cooled by oil. The RR oiling system has a significant increase in oil capacity... for better cooling. I like the beauty and simple clean looks of air-cooled. Radiators are ugly and vulnerable to damage and I tend to get lazy and don't want to change the coolant in my motorcycles. So the RR engine is what I am hoping for. | ||
| 45_degrees |
I couldn't tell you why they changed Spatten1. Might be because of noise pollution... I don't know. I do know that the 911 lost a lot of it's character when they changed... doesn't sound as good to some people... lost it's raw, refined mechanical seeming nature. The new ones really aren't that much more powerful I don't think. They sure are ugly compared to the old air-cooled ones IMO. My point is that Duc says high-power air-cooled engines are grenades and that is a false statement. | ||
| Borrowedbike |
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| Spatten1 |
"Radiators are ugly" True | ||
| 45_degrees |
There are advantages and disadvantages to both designs... I prefer this engine and it's air-coolness. All the rest of the Buell innovative designs and features are just icing on the cake for me. I guess you guys bought Buell for the radical design and the engine was the turd in your mornin' cup of coffee. I think the bike is synergy with this engine and I don't mind if they decide to make this engine more powerful. | ||
| Spatten1 |
"I guess you guys bought Buell for the radical design and the engine was the turd in your mornin' cup of coffee." There is some truth to that for me, also that it is American. I've come the really love the engine for easy riding. It has a very unique feel to it and is very soothing. For moderate street riding it is way fun and very satisfying. When I really need to drop the hammer, this engine just doesn't cut it. I found myself taking way too many chances at the track trying to overcome the lack of power. It was just too dangerous of a way to ride, for me. I also seem to be very good a breaking Buell engines. One of my talents I guess. | ||
| Socalbueller |
Who said Buell can't have both a water-cooled AND a air-cooled engine? Almost every other make of motorcycle has both kinds of engines. | ||
| Spatten1 |
Both would be the way to go. Keep with the heritage and also improve, like Ducati. | ||
| Tpoppa |
"Radiators are ugly" So are Mirrors, Turn Signals, License plate brackets, and many riders...and none of those have the potential to add power. | ||
| Yohinan |
Whats wrong with as mentioned above using something like the RR's added oil capacity and larger oil cooler. Not sure how that would apply but.... On more than one occasion in the 4 wheel world when needing added block strength we will hard blok fill an engine block. To overcome the lost water cooling the oil system capacity is greatly increased and a much larger oil cooler is added. This method works, as it is even used in street driven machines without longevity problems. You have eliminated the need for water cooling by using a much larger oiling system. Just food for thought....... | ||
| Jaimec |
If you're going to air cool the cylinders, then stick them out where they'll actually get some air. BMW has known this since 1923... Looks too ungainly? Then tuck the cylinders away, but then water cool them so you don't cook the jugs not directly in the airflow. Either that, or install a bunch of fugly air scoops and a loud, annoying fan... | ||
| Eboos |
 "Either that, or install a bunch of fugly air scoops and a loud, annoying fan..." |
