4 ms·

Neither can an internal combustion, of course. When doing a max speed test, holding high horsepower output levels for a long time, an internal combustion engine

Neither can an internal combustion, of course. When doing a max speed test, holding high horsepower output levels for a long time, an internal combustion engine will overheat quickly. That's true even with massive airflow over large liquid radiators, with coolant flowing through the casting along the cylinder walls - not to mention literally being a pump which moves cold air in and hot exhaust out at a rate of thousands of liters per minute. In both cases, it's fine that the power doesn't last, because it takes merely 10-20 horsepower (7.5-15 kW) to move an average car on a flat road at 60 MPH/100 km/h. To accelerate to that cruising speed in ten seconds takes about 180 horsepower/135 kW. I had the pleasure last week of working on an industrial vacuum pump installation with twelve 100-horsepower/75 kW electric motors - these guys: https://www.baldor.com/catalog/EM4400TS https://www.baldor.com/catalog/EM4400TS Don't look at the photo and think "Oh yeah, there's one of those hanging on the back of my dad's drill press." The shaft is the size of your wrist, not your finger. The casting is the size of an oil drum, and it is made from extremely dense cast iron and copper on a level that non-metalworkers probably don't understand: It weighs 1,200 lbs/550 kg. Size absolutely is the issue! That sort of motor would be a terrible powerplant for an electric vehicle: It MUST be made very much smaller and very much more powerful. It's made that way because an industrial motor needs to be able to dissipate 4.6% of that max rated 75 kW (acting as a 3,450W space heater) as heat while running at full power for days, covered in dirt and debris, spinning tirelessly in the desert sun, probably with a significant safety factor on all those numbers. Industrial motors are not the same as EV motors!

sandworm101 5y ago
>> holding high horsepower output levels for a long time, an internal combustion engine will overheat quickly. Every racecar in every 24-hour race. Every large boat/ship that runs at full throttle 24/7. Every large truck pulling a load up a hill. Every diesel generator that runs at full load for weeks. Modern IC engines can run flat-out for considerable periods of time. Counterintuitively, in many ways running at high power settings is easier on an IC engine than at lower fuel-efficient setting. Some pressures between parts are lower at higher RPMs. Total power/RPM is higher, but the energy involved in each rotation of a part is generally less. Oil moves more efficiently and doesn't get squeezed out as parts push against each other. And the ignition inside the cylinder is richer (ie cooler) when optimized for power rather than efficiency. Talk to anyone riding a Japanese sportbike. Those engines are far happier running flat-out on the track than sitting at idle in traffic.
- Workaccount2 5y ago
  Those long durations just mean that they (the engine designers) are taking thermals into consideration, and capping at a lower power to compensate. What you think is flat out, is really just "max it can run without burning up".
  - sandworm101 5y ago
    No. Flat-out means at full RPM, which is not a thermal decision. It is a limit based on cylinder size and flame speed. Any higher and the fire is still burning when the exhaust valve opens. That is why engines with big/wide cylinders cannot turn as quickly. This is why a large ship with 2-foot wide cylinders might max out at 100rpm while a sportbike with 1-inch cylinders might at 16,000rpm. The capacity of the cooling system is a different issue. Because of the physics of air movement, sitting at idle is very hard on a car engine. Idle means no speed and air has to be forced across the radiator. Flat-out would mean at least some forward movement and lots of air across the radiators. Any radiator system meant to survived idle while stopped will handle flat-out at speed indefinitely. Those Japanese sportbikes racing around the track are not overheating, but they might if asked to idle at the start line for too long. Where I am, it is normal to see cars/trucks with carboard across their fronts to reduce airflow. In winter there is too much cooling and engines have trouble getting up to temperature at any forward speed. This is a big issue if you are relying on the engine to warm up and de-fog your windscreen (hybrids). https://www.cbc.ca/news/business/honda-crv-civic-heater-1.5960676 https://www.cbc.ca/news/business/honda-crv-civic-heater-1.59...
    - toss1 5y ago
      >> Flat-out means at full RPM, which is not a thermal decision. It is a limit based on cylinder size and flame speed. Any higher and the fire is still burning when the exhaust valve opens. Partially -with some engines, the limit is valve float, or cam shape (which is why electronically operated valves are becoming a thing), with some it is thermal. With pro-level drag race cars, producing 7000+ Hp / 5+MW, some of the more key considerations are how much fuel can be pumped into the cylinders. But they turn over only something like 900 revolutions each race run and need to be torn down between each run. The point is that ICE engine design is a massive balancing act between inertia of parts, internal friction, strength of parts, fuel, and thermal. Thermal may not be the main driver of every engine design, but if you claim thermal is irrelevant and not a limiting factor, you're just plain wrong. In many types of road races from F1 to Le Mans, merely picking up a small sheet of plastic or paper on the radiator intake will be a cause to pit almost immediately because the thermal management is designed to handle the requirements.
KennyBlanken 5y ago
> When doing a max speed test, holding high horsepower output levels for a long time, an internal combustion engine will overheat quickly. That's true even with massive airflow over large liquid radiators, with coolant flowing through the casting along the cylinder walls - not to mention literally being a pump which moves cold air in and hot exhaust out at a rate of thousands of liters per minute. No? Many passenger cars do not have sufficient oil cooling capacity to handle continuous high speed high power running, because it's not necessary. That doesn't mean internal combustion engines in general can't. Airplane engines run at max power most of their life and the piston variant is typically only air and oil cooled. Plenty of race car engines operate at near their maximum power and RPM limits for long periods of time. Lots of cars can in fact operate at maximum power for long periods of time (see: Autobahn.) Train internal combustion engines can operate at maximum power continuously. Generator engines from home to megawatt size operate at max power continuously. Stick to what you know, friend.

sandworm101 5y ago

>> holding high horsepower output levels for a long time, an internal combustion engine will overheat quickly. Every racecar in every 24-hour race. Every large boat/ship that runs at full throttle 24/7. Every large truck pulling a load up a hill. Every diesel generator that runs at full load for weeks. Modern IC engines can run flat-out for considerable periods of time. Counterintuitively, in many ways running at high power settings is easier on an IC engine than at lower fuel-efficient setting. Some pressures between parts are lower at higher RPMs. Total power/RPM is higher, but the energy involved in each rotation of a part is generally less. Oil moves more efficiently and doesn't get squeezed out as parts push against each other. And the ignition inside the cylinder is richer (ie cooler) when optimized for power rather than efficiency. Talk to anyone riding a Japanese sportbike. Those engines are far happier running flat-out on the track than sitting at idle in traffic.

Workaccount2 5y ago
Those long durations just mean that they (the engine designers) are taking thermals into consideration, and capping at a lower power to compensate. What you think is flat out, is really just "max it can run without burning up".
- sandworm101 5y ago
  No. Flat-out means at full RPM, which is not a thermal decision. It is a limit based on cylinder size and flame speed. Any higher and the fire is still burning when the exhaust valve opens. That is why engines with big/wide cylinders cannot turn as quickly. This is why a large ship with 2-foot wide cylinders might max out at 100rpm while a sportbike with 1-inch cylinders might at 16,000rpm. The capacity of the cooling system is a different issue. Because of the physics of air movement, sitting at idle is very hard on a car engine. Idle means no speed and air has to be forced across the radiator. Flat-out would mean at least some forward movement and lots of air across the radiators. Any radiator system meant to survived idle while stopped will handle flat-out at speed indefinitely. Those Japanese sportbikes racing around the track are not overheating, but they might if asked to idle at the start line for too long. Where I am, it is normal to see cars/trucks with carboard across their fronts to reduce airflow. In winter there is too much cooling and engines have trouble getting up to temperature at any forward speed. This is a big issue if you are relying on the engine to warm up and de-fog your windscreen (hybrids). https://www.cbc.ca/news/business/honda-crv-civic-heater-1.5960676 https://www.cbc.ca/news/business/honda-crv-civic-heater-1.59...
  - toss1 5y ago
    >> Flat-out means at full RPM, which is not a thermal decision. It is a limit based on cylinder size and flame speed. Any higher and the fire is still burning when the exhaust valve opens. Partially -with some engines, the limit is valve float, or cam shape (which is why electronically operated valves are becoming a thing), with some it is thermal. With pro-level drag race cars, producing 7000+ Hp / 5+MW, some of the more key considerations are how much fuel can be pumped into the cylinders. But they turn over only something like 900 revolutions each race run and need to be torn down between each run. The point is that ICE engine design is a massive balancing act between inertia of parts, internal friction, strength of parts, fuel, and thermal. Thermal may not be the main driver of every engine design, but if you claim thermal is irrelevant and not a limiting factor, you're just plain wrong. In many types of road races from F1 to Le Mans, merely picking up a small sheet of plastic or paper on the radiator intake will be a cause to pit almost immediately because the thermal management is designed to handle the requirements.

KennyBlanken 5y ago

> When doing a max speed test, holding high horsepower output levels for a long time, an internal combustion engine will overheat quickly. That's true even with massive airflow over large liquid radiators, with coolant flowing through the casting along the cylinder walls - not to mention literally being a pump which moves cold air in and hot exhaust out at a rate of thousands of liters per minute. No? Many passenger cars do not have sufficient oil cooling capacity to handle continuous high speed high power running, because it's not necessary. That doesn't mean internal combustion engines in general can't. Airplane engines run at max power most of their life and the piston variant is typically only air and oil cooled. Plenty of race car engines operate at near their maximum power and RPM limits for long periods of time. Lots of cars can in fact operate at maximum power for long periods of time (see: Autobahn.) Train internal combustion engines can operate at maximum power continuously. Generator engines from home to megawatt size operate at max power continuously. Stick to what you know, friend.