I read that a massive portion of usable energy is wasted and turned to heat instead of being used to turn the crankshaft — would there be like any way of reducing the heat/cooling the engine so you could get 50-70% thermal efficiency?
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There are a lot of losses. You hear the engine? That’s energy being lost. Every moving component has friction. You need energy to overcome that friction.
The exhaust gasses are hot, which is also energy being lost through the exhaust.
These losses are before you even consider the large amount of heat put into the cooling system, which is lost to the environment through the radiator.
You can harness this energy in a similar way to how your car heating system works using stationary engines. The cooling system carries heat to the heater matrix and a fan blows air through it to heat your cabin. This same principle is used in combined heat and power gensets where they use the heat energy to feed radiators or hot water systems.
In this application, the engine is used to drive an alternator to supply a building with electricity. Usually, the engine just gets rid of this heat through the exhaust and radiator, however in a CHP they use a jacket around the exhaust and sometimes through the cooling system. They pass the heat into water, and it’s fed into a building using a heat exchanger.
Efficiencies here can be in the high 80s or more, especially if used for cooling too.
There are a lot of losses. You hear the engine? That’s energy being lost. Every moving component has friction. You need energy to overcome that friction.
The exhaust gasses are hot, which is also energy being lost through the exhaust.
These losses are before you even consider the large amount of heat put into the cooling system, which is lost to the environment through the radiator.
You can harness this energy in a similar way to how your car heating system works using stationary engines. The cooling system carries heat to the heater matrix and a fan blows air through it to heat your cabin. This same principle is used in combined heat and power gensets where they use the heat energy to feed radiators or hot water systems.
In this application, the engine is used to drive an alternator to supply a building with electricity. Usually, the engine just gets rid of this heat through the exhaust and radiator, however in a CHP they use a jacket around the exhaust and sometimes through the cooling system. They pass the heat into water, and it’s fed into a building using a heat exchanger.
Efficiencies here can be in the high 80s or more, especially if used for cooling too.
Oh I gotchu.
So ICE’s rely on combusting to operate, and this combustion generates heat as its primary output mechanism. That’s in fact the thing we’re taking advantage of.
Pistons get pushed because the air inside of the space rapidly expands in the heat, generating the pushing motion we use to propel us forward. The goal of the thing is to make heat.
So actually we want the heat in the first place!
The issue is, and probably what you’re referring to, is that the heat doesn’t all go to expand the air inside the piston – some of it gets lost to the block and surrounding area. Most of it goes out the tailpipe after being used once (assuming no turbo).
We can cool the block sure! But that’s not really making the engine more efficient, that’s just increasing the thermal load of the material since it being colder just means it can absorb more heat before melting. If we also cool it actively using some sort of coolant than we need a water pump to circulate that coolant, which you attach to the crankshaft; which means that you’re wasting more energy generated to cool the system.
Now you can build the engine out of a material that’s more insulative; but then the issue is that your block will melt quite quickly. You want the cold (relatively speaking to you and I it’s still very hot) to keep the thing going. If you imagine a fictional exercise where you’re able to lose no heat in a piston, it won’t be long before the inside becomes as hot as the surface of the sun. And there’s no known material that could support that.
Turbo chargers are an interesting way to increase thermal efficiency though! They use the hot air generated to passively spin a turbine that allows you to take in more air that further increases the combustion!
Unfortunately at the end of the day burning things for fuel just isn’t all that great. Electric vehicles are far better about this because their primary mechanism isn’t heat, but electromagnetism!
An electric motor works by sending a current through a magnetic; rapidly switching its polarity enough to spin with quite a bit of force. It’s wildly simple and far more efficiency than directly generating heat for fuel!
F1 engines have been able to achieve over 50% thermal efficiency by recovering heat with a now deprecated device called the MGU-H. Combined with a turbo charger to recover exhaust energy and kinetic energy via braking with what used to be referred to as the MGU-K, an F1 engine is probaly one of the most efficient engine systems that the world has ever seen.
Oh I gotchu.
So ICE’s rely on combusting to operate, and this combustion generates heat as its primary output mechanism. That’s in fact the thing we’re taking advantage of.
Pistons get pushed because the air inside of the space rapidly expands in the heat, generating the pushing motion we use to propel us forward. The goal of the thing is to make heat.
So actually we want the heat in the first place!
The issue is, and probably what you’re referring to, is that the heat doesn’t all go to expand the air inside the piston – some of it gets lost to the block and surrounding area. Most of it goes out the tailpipe after being used once (assuming no turbo).
We can cool the block sure! But that’s not really making the engine more efficient, that’s just increasing the thermal load of the material since it being colder just means it can absorb more heat before melting. If we also cool it actively using some sort of coolant than we need a water pump to circulate that coolant, which you attach to the crankshaft; which means that you’re wasting more energy generated to cool the system.
Now you can build the engine out of a material that’s more insulative; but then the issue is that your block will melt quite quickly. You want the cold (relatively speaking to you and I it’s still very hot) to keep the thing going. If you imagine a fictional exercise where you’re able to lose no heat in a piston, it won’t be long before the inside becomes as hot as the surface of the sun. And there’s no known material that could support that.
Turbo chargers are an interesting way to increase thermal efficiency though! They use the hot air generated to passively spin a turbine that allows you to take in more air that further increases the combustion!
Unfortunately at the end of the day burning things for fuel just isn’t all that great. Electric vehicles are far better about this because their primary mechanism isn’t heat, but electromagnetism!
An electric motor works by sending a current through a magnetic; rapidly switching its polarity enough to spin with quite a bit of force. It’s wildly simple and far more efficiency than directly generating heat for fuel!
F1 engines have been able to achieve over 50% thermal efficiency by recovering heat with a now deprecated device called the MGU-H. Combined with a turbo charger to recover exhaust energy and kinetic energy via braking with what used to be referred to as the MGU-K, an F1 engine is probaly one of the most efficient engine systems that the world has ever seen.
Others have approached this but missed the point – there are commercial engines which are far over 20-30% in routine use.
20-30% is about right for crappy 4-stroke.
For example – this normally aspirated 160cc honda engine https://www.justgenerators.co.uk/honda-gx160-qhq4-engine.html uses 313g/kWh.
1kg of petrol is around 44MJ/kg, so this is 13.7MJ input per hour, and 3.6MJ out.
This is 26%, and this is a mediochre 160cc 4 stroke single cylinder engine with nearly no economy measures.
To hit 20%, you need a really badly malfunctioning engine, a very old one, or one operating far from its ideal operating point. Or a 2-stroke.
https://en.wikipedia.org/wiki/Brake-specific_fuel_consumption is the page you want.
Some highlights.
The first ever functional diesel engine hit 26%. (1931)
The engines of the B29 hit 35% on avgas (35%)
Napier Nomad (experimental aero engine) hit 40% in 1949.
On a more commercial note the 2000s Volkswagen 3.3 V8 TDI got to 41%.
Gasoline in the Toyota 1NZ-FXE (prius) at about the same time being a few points down at 36%. Cars have not meaningfully improved since then.
The top of the pile are large marine engines that are hitting 55%, and stationary gas turbines at 60%.
But, we’ve had >30% internal combustion engines in routine use since the 1920s, >40% since the 30s and 60% for around a decade. (the last being jet engines)
These are the best fuel efficiencies at any RPM, often 60% max power output or so for gasoline, a bit more for diesel.
Others have approached this but missed the point – there are commercial engines which are far over 20-30% in routine use.
20-30% is about right for crappy 4-stroke.
For example – this normally aspirated 160cc honda engine https://www.justgenerators.co.uk/honda-gx160-qhq4-engine.html uses 313g/kWh.
1kg of petrol is around 44MJ/kg, so this is 13.7MJ input per hour, and 3.6MJ out.
This is 26%, and this is a mediochre 160cc 4 stroke single cylinder engine with nearly no economy measures.
To hit 20%, you need a really badly malfunctioning engine, a very old one, or one operating far from its ideal operating point. Or a 2-stroke.
https://en.wikipedia.org/wiki/Brake-specific_fuel_consumption is the page you want.
Some highlights.
The first ever functional diesel engine hit 26%. (1931)
The engines of the B29 hit 35% on avgas (35%)
Napier Nomad (experimental aero engine) hit 40% in 1949.
On a more commercial note the 2000s Volkswagen 3.3 V8 TDI got to 41%.
Gasoline in the Toyota 1NZ-FXE (prius) at about the same time being a few points down at 36%. Cars have not meaningfully improved since then.
The top of the pile are large marine engines that are hitting 55%, and stationary gas turbines at 60%.
But, we’ve had >30% internal combustion engines in routine use since the 1920s, >40% since the 30s and 60% for around a decade. (the last being jet engines)
These are the best fuel efficiencies at any RPM, often 60% max power output or so for gasoline, a bit more for diesel.
Internal combustion engines are named that because they have a fire in them that makes heat. The heat is used by the engine to make forces to move the car. Heat is a form of energy that is very useful, but it is complicated to convert it to other forms. So most of the energy, “leaks out,” instead of moving the car. Some examples of the leakage are: some heat can’t be used because it is too, “cold,” to be used and some heat is lost due to things moving and rubbing on other things. When you’re older, it might be fun to talk about the Otto cycle and do some math together.
Internal combustion engines are named that because they have a fire in them that makes heat. The heat is used by the engine to make forces to move the car. Heat is a form of energy that is very useful, but it is complicated to convert it to other forms. So most of the energy, “leaks out,” instead of moving the car. Some examples of the leakage are: some heat can’t be used because it is too, “cold,” to be used and some heat is lost due to things moving and rubbing on other things. When you’re older, it might be fun to talk about the Otto cycle and do some math together.
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