Turbocharged Hybrids

[Isaac Zachary]

The question is how much efficiency is lost to "oversizing" the engine (compared to steady flat cruising needs) and how much would be lost to a hybrid system.

Looking at this graph, if we assume the car needs a steady 15kW (about 20hp) of power to cruise at a steady highway speed, it would use at best 260g/kWh (about 32.4% efficient) with perfect gearing. But the most efficient the engine would be would be 245g/kWh (about 34.4% efficient) and would give at most 58kW (about 78hp) of power at that efficiency (with perfect gearing). The most power the engine could produce is about 85kW (114hp) but would use around 300g/kWh (28.1%) with perfect gearing.

But if you were to extrapolate the numbers to accomodate a +200hp engine then it could easily fall to the 300g/kWh ring just cruising.

[redpoint5]

Originally Posted by Isaac Zachary

The question is how much efficiency is lost to "oversizing" the engine (compared to steady flat cruising needs) and how much would be lost to a hybrid system.

Looking at this graph, if we assume the car needs a steady 15kW (about 20hp) of power to cruise at a steady highway speed, it would use at best 260g/kWh (about 32.4% efficient) with perfect gearing. But the most efficient the engine would be would be 245g/kWh (about 34.4% efficient) and would give at most 58kW (about 78hp) of power at that efficiency (with perfect gearing). The most power the engine could produce is about 85kW (114hp) but would use around 300g/kWh (28.1%) with perfect gearing.

But if you were to extrapolate the numbers to accomodate a +200hp engine then it could easily fall to the 300g/kWh ring just cruising.

I'm not sure I'm tracking your question entirely.

Maybe it would be best to target peak efficiency of the engine at 30 HP so it could cover steady cruise plus a tiny bit of battery charging, but allow the engine to operate outside of peak efficiency if there's high demand, like ascending a hill or driving 90 MPH. ICE perform reasonably efficiently even at high output, it's just the low output where they are abysmal.

[Isaac Zachary]

What I'm saying is that from 20% to 80% power you're not going to be hit very hard on efficiency. Therefore a traditional hybrid makes sense, something that may limit the engine's power to around 100hp maximum but makes up for it with the hybrid portion.

By making a series hybrid with a tiny "perfect sized" engine you might not gain enough efficiency to make up for the losses through the hybrid portion of it.

[redpoint5]

Seems clear that the larger the vehicle, the more likely a series hybrid makes sense. Trains are clearly large enough to warrant a series hybrid design.

I recall seeing a proposal for a jet-powered series hybrid garbage truck that seemed to make sense.

... the 50 MPG proposed efficiency in the OP is nothing to scoff at. Say you could get 55 MPG by going parallel hybrid. Does that warrant the complexity and cost of that drivetrain? More efficient isn't always more efficient.

[Should be biking]

Originally Posted by Isaac Zachary

By making a series hybrid with a tiny "perfect sized" engine you might not gain enough efficiency to make up for the losses through the hybrid portion of it.

Sounds like you get my point. Cheers

[cRiPpLe_rOoStEr]

Originally Posted by redpoint5

I recall seeing a proposal for a jet-powered series hybrid garbage truck that seemed to make sense.

I remember it too, the Wrightspeed powertrain project. One advantage of the microturbine engine was its capability to handle basically any fuel, including landfill gas.

Microturbines, or a turboshaft engine for those more familiar with helicopters, seem quite reasonable for a series hybrid, as they tend to operate better at a steady RPM and throttle-response is too slow for making good use of any other driveline.

[JSH]

Originally Posted by redpoint5

What do you call it? It's not a gas pedal because it burns oil. Oil pedal?

... and what people think is a gas pedal is the throttle which determines how much air the engine ingests, and in response, how much fuel to add.

... and what people think is the throttle these days is a pedal position sensor where the driver can suggest to the computer what power level they intend, and the computer decides both throttle opening and quantity of fuel to add.

Accelerator pedal works for any ICE vehicle. Diesels don't use gas nor do they have a throttle body.

With EVs the right most pedal controls acceleration and braking.

[Should be biking]

I think what redpoint5 meant was that gas pedal doesn’t apply for a lot of cars nowadays.
A lot of diesel actually have an intake throttle now to help increase EGR flow.

[cRiPpLe_rOoStEr]

Originally Posted by Should be biking

A lot of diesel actually have an intake throttle now to help increase EGR flow.

It's also meant to increase EGT faster while doing the DPF regen.

[ismailkho]

To summarize, there are several reasons why there are no turbocharged hybrids on the market. The Atkinson cycle, which is commonly used in hybrid vehicles, is designed to optimize fuel efficiency rather than power. Adding a turbocharger to a hybrid powertrain would introduce additional complexity and cost, and may be difficult to integrate with the hybrid control systems in a way that maintains good fuel efficiency and performance. While it is possible to turbocharge a hybrid vehicle aftermarket, it may not result in better efficiency compared to a non-hybrid vehicle with equivalent power. The best way to increase power and maintain good fuel efficiency in a hybrid vehicle is to use a larger, more powerful hybrid powertrain from the factory.