I’m hearing more and more about “electric turbo-chargers,” (a motor-generator shafted to an IC engine’s TC). I gather that the idea is that when it motors the compressor it aids with spool-up and load changing (which makes it less polluting & more efficient, the glossy print-out says); and in genny mode it harvests extra electricity when loads are steady (Bowman claims 10% more than the genset its attached to).

Anyone seen one in the wild on a marine installation?

1 Like

That’s a neat trick, recovering more energy from the exhaust than from the crankshaft is what I call voodoo engineering.

Consider that the typical slow speed diesel converts about 50 percent of the input energy to the shaft and about 25 percent to the exhaust gas.

Yah, I know. Sankey is scratching his head.

I think they mean 10% of the genset’s power comes from the TC alternator… but still, really?

Like out of every 100 kWatts, 90 are from the crank and 10 are from the TC? Or possibly: for each 110 kW, 100 from the crank and 10 from the TC. Promo material doesn’t make these points clear. Also, most of the applications mentioned are high speed engines.

Since the proportion of energy available from a high speed engine is usually greater than that of a slow speed engine perhaps they should use the generator to turn a compressor that delivers hot air to the TC and maybe at some point they can stop fueling and run off the magic energy alone.

Wow! What a brilliant idea! I’m going to file the provisional patent this morning.

In real life it is not unreasonable to expect to recover 10 percent or more of the exhaust gas energy (waste heat) to power a steam turbine generator. That has been done for years.

Is it reasonable that there might be more kinetic energy available than required to drive a turbo at high RPMs but less than required at low rpm? Maybe not a low-speed diesel but what about a high-speed diesel?

My understanding is that it is heat energy rather than kinetic energy that motivates an exhaust gas or steam turbine. Its not a windmill.

1 Like

It sounds to me more like a turbine connected downstream of the existing engine turbocharger turbine in the exhaust stream to take additional energy from the exhaust and make electricity…would have to see a picture/diagram to be certain.

I know Detroit Diesel, Scania and Volvo had a similar concept with the downstream turbine feeding the geartrain directly for additional horsepower on their over-the-road truck engines in the early 2000’s

Ya, That config was mentioned as a retrofit possibility, along with having the e-tc (or 2 in parallel) as the primary TC

So if I understand correct an electric motor driven compressor with a regular turbocharger in parallel for combustion air and an additional turbine shafted to a generator for electrical generation on the exhaust.

Wow…just sounds like a lot of equipment for not a lot of gain, however if emissions is the driving force the cost will be a pass-through.

Interesting idea, I have never heard of anyone doing this (yet) - would like to see some pictures or documentation on the system if you could dig it up!

You are correct. A turbine is a calorie machine. It uses calories for nutrition to give it energy to make motion. Just like we do. Once in motion turbines are relatively efficient [unlike us] especially if they use heat that would normally have no other use. Extraction turbines are really cool machines to have around if you have heat needs for other purposes.

No-ah. Nothing that elaborate.

The compressor-turbine as normal (they claim special geometric efficiencies, but more or less as normal). Except coupled by a shaft to a magneto-motive motor-generator. So you run it as a motor during start-up and load changes to compress a more efficient air charge and avoid soot. Once you have your good running RPMs you let the turbine run the thingy as a generator and get your “10%” kW out, or whatever your salesman promised. That’s the unit.

So you can install this unit after your conventional turbine, or instead of your conventional TC, or 2 units in parallel, or one for each bank, or what-ever you fancy.

That is the bottom line, that post says it all.

There are benefits to motorizing the turbo driven generator to accelerate the turbocompressor to aid in engine acceleration or load increase. When the load is at a steady state the “waste heat” in the exhaust can be recovered and converted to electrical power by the motor/generator.

1 Like

If this was adapted to a slow speed engine you could say goodbye to auxiliary blowers.

1 Like

Any of you recall the “turbo-compound” aircraft engines of the 40’s? The Pratt & Whitney R-4430 (I think all that is correct…) had four interconnected 9 cylinder radial engines on one crankshaft nick-named “corncob.” Each series or layer of engine had an exhaust driven turbine mechnically connected to the crank by bevel gears to recover energy from the exhaust gases.

There has to be a point of diminishing returns on such schemes that should be determined by actual dynomometer testing. There probably is some math that may predict that point but actual testing would be the proof. Land speed record attempts and the air races of the 20’s and 30’s pretty well showed how actual performance had the final word.

I mean, they have been in production for a time now, they do work. I just never saw one myself. Spool-up with compressed air I’ve seen, I guess many of us have… just not electric motor.

It was the two row 18 cylinder Wright 3350, not the 4 row 28 cylinder PW 4360 that used PRTs.

The power recovery turbines added about 20 percent more power at takeoff but were problematic as the fluid drives were very good lube oil centrifuges and were prone to vibration issues when the oil sludge locked them “on”.

They were not interconnected engines any more than a V8 engine is 4 interconnected 2 cylinder engines - let’s not talk about DD 16V92 engines please.

I’ve also heard about exhaust gas power turbines, but never outside the classroom. To understand why they are beneficial, we must examine why adding a turbocharger to a piston engine can improve adiabatic efficiency. The keyword is pumping losses; In a naturally aspirated, high speed diesel engine operating under ideal conditions, roughly 12% of the input energy is spent on pumping air. This is analogous to the power needed to turn the engine at rated speed (excluding compression heat loss).

There is plenty of energy left in the working fluid (exhaust gas) when it leaves the cylinder, evidenced by the sharp pressure drop on your indicator card as the exhaust valve opens. The TC harnesses this energy to do a part of the pumping work, and does so with a pump type (radial flow kinetic or compound axial-radial) that is far more efficient at low pressure differentials than a piston pump. You effectively end up with a multi stage pumping system where each stage is better matched to its delta-p, and use surplus energy to do so. Very roughly speaking, if you have 3 bar boost and 30 bar compression, you eliminate 2/3 of the pumping power needed by the piston stage (engine). There is a myriad of losses and inefficiencies that keep you from reaching this figure, which I barely understand and certainly won’t get into here, but there’s enough left to see an efficiency increase under certain conditions.

As it happens, there’s more surplus energy available in the exhaust gas than can be used for pressurizing induction air within practical limits, and this is where the exhaust gas power turbine comes in. No black magic, just thermodynamics (which is pretty close imho). I believe the only thing limiting the use of these is the added cost and complexity.

What? Practically every turbo out there is driven by a simple impulse turbine (aside from esoteric examples with an axial flow reaction stage). They are dependent on exhaust gas temperature only because gas enthalpy affects velocity.

1 Like

Mass flow!

Now standby, gentlemen. We can resolve this peacefully. Heat, pressure, mass flow, velocity, or temperature? Take a deep breath and look deeply into the nature of the universe: