Turbo/Generator

[Neutrino]

Well an ideea came a me a while ago. As we all know hybrid gasoline/electric cars do recover some energy during braking by transforming into electrical energy to recharge the batteries.

And I was thinking why not take this a step further and install a turbo to recover some of the energy going trough the exaust while the internal combustion engine is working. But this turbo instead of driving a compressor to force air into the engine it drives an electric generator to recharge the batteries

[kcap122]

your saying basically use a turbo to drive the alternator?


....thats awesome.

[Neutrino]

Originally Posted by kcap122

your saying basically use a turbo to drive the alternator?


....thats awesome.

basically yes

[MagicRat]

Originally Posted by Neutrino

Well an ideea came a me a while ago. As we all know hybrid gasoline/electric cars do recover some energy during braking by transforming into electrical energy to recharge the batteries.

And I was thinking why not take this a step further and install a turbo to recover some of the energy going trough the exaust while the internal combustion engine is working. But this turbo instead of driving a compressor to force air into the engine it drives an electric generator to recharge the batteries

In a word, yes. The idea with a turbo is to reclaim wasted thermal energy in expaning exhaust gases. Pressurizing the intake manifold, as we see with gas and diesel engines is only one way use the energy.

Having the turbo turn a generator is fine, although you have losses due to induction, that is, you get less electrical energy out of the generator than what you put in.

Another way is to physically connect the turbo shaft to the crankshaft, although this works best in engines that turn at a constant speed, such as airplanes and ships.

Back in the 1950's, in England, Napier, a builder of industrial and aircraft engines applied this principle to its piston engine aircraft engines. It had turbos that helped turn the propeller, improving efficiency.

The problem here is that the gas turbine (jet) engine is more thermally efficient, at a constant speed, than any piston engine can hope to be, so this technology, at least in aircraft and high speed (military) ships was a dead end.

[Reed]

many large reciprocating aircraft engines had whats called a power recovery turbine where a set a turbines is used in the exhaust to recover the energy there and place it directly to the crank through some gearing.

so i guess you could use the exhaust energy for a lot of things although i dont thing the power loss from a turbine being in the exhaust path would overcome the gain from taking off an alternator

[SaabJohan]

Turbocompound is currently in serial production in heavy trucks and have been around since the world war 2 when it was used in airplane engines.

The powerloss from the restriction caused by the turbine is almost zero while the turbine will develope a few percent of the total engine power. Since the turbine can extract quite much power I would not recommend that it's used to power an alternator, the output is also load dependant which means at idle the output is almost zero and the car will need another alternator anyway.

Any type of thrust engines is not suitable for cars as they give a high fuel consumption. As for turboshafts, the land veichle and helicopter engines are about as efficient as an otto engine, around 30%, with an increasing efficiency with increased combustion temperature. If the compressor outlet temperature is equal to the turbine outlet temperature it's 50% efficient, the rest is used to power the compressor, which means that a gas turbine engine is very dependant on the efficiencies of it's compressor and turbine and can easily drop in efficiency. The larger gas turbines used in for example ships are usually 40-45% efficient, which is lower than for a diesel piston engine, the engines are however much smaller and lighter for a given power so they are used where performance is important.

[MagicRat]

Originally Posted by SaabJohan

Turbocompound is currently in serial production in heavy trucks and have been around since the world war 2 when it was used in airplane engines.

The powerloss from the restriction caused by the turbine is almost zero while the turbine will develope a few percent of the total engine power. Since the turbine can extract quite much power I would not recommend that it's used to power an alternator, the output is also load dependant which means at idle the output is almost zero and the car will need another alternator anyway.

Any type of thrust engines is not suitable for cars as they give a high fuel consumption. As for turboshafts, the land veichle and helicopter engines are about as efficient as an otto engine, around 30%, with an increasing efficiency with increased combustion temperature. If the compressor outlet temperature is equal to the turbine outlet temperature it's 50% efficient, the rest is used to power the compressor, which means that a gas turbine engine is very dependant on the efficiencies of it's compressor and turbine and can easily drop in efficiency. The larger gas turbines used in for example ships are usually 40-45% efficient, which is lower than for a diesel piston engine, the engines are however much smaller and lighter for a given power so they are used where performance is important.

Absolutely, gas turbine engines are at their most efficient running at a constant load and rpm, hence their use in shipping, aircraft, generators and compressors, such as for natural gas pipeline pumps.
I have wondered if such an engine would work in diesel electric railway locomotives. The typical GM-built locomotive uses V-16 diesel engines to turn generators. The application would be suitable to gas turbine engines. Heat exchangers could be used to warm up the intake air, something that cannot be done with a thrust engine.

[SaabJohan]

Gas turbines have been used in trains, at least of the smaller type that transports people without any separate locomotive. The turbines then produce the electricity that powers the electric motors that turn the wheels. Here there are probably space issues which isn't the case with a locomotive so there are no reason to switch to a more expensive less efficient turboshaft engine just because they are more powerful for their size/weight.

Only very large engines heat up the intake air, it's then done after the compressor with a heat exchanger that takes the heat from the exhaust.

If I remember correctly the typical diesel electric railway locomotive produces a couple of thousands hp. This means that the diesel should be replaceable with for example an GE LM500 or a single or dual setup of GE T64 engines and these engines are not what you can call fuel efficient, 198 and 212 g/hp and hour is what they consume, and worse at part load. A GE T64 engine in one of its more powerful versions also cost over a million dollars.