Why aren't diesel hybrids being used?

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I am thinking in terms of a mostly electric car that uses something like a small 2-3 cylinder diesel to spin a large generator to give the battery a longer charge.

I suppose in a pinch it could run the car as an emergency back up.
 
Cost, weight, and emissions control system complexity are too much with a diesel in car hybrid applications.
You do see hybrid transit buses using diesel engines.
Engineers struggle to keep production costs down on hybrids, what with all the batteries and electrics they have to build and stuff in there. Hybrids also tend to be too heavy when you add batteries etc., so the rest of the car needs to be on a weight-loss diet.
 
Diesels take a long time to warm up. Until they are warmed up, the engine is inefficient.
 
Will be interesting to see what others think about this. The vehicle could run off the electric motor but the diesel would kick in when the battery discharged below a certain point. It would work like a plug-in hybrid to allow zero emissions for shorter trips, and low emissions for longer highway cruising with a several hundred mile range.

Turbo diesels can be highly efficient, especially when used at more constant loads such as charging a battery and running the electric motor at cruising speed. It wouldn't have to deal with the challenges of prolonged idling, and could be tuned for very low emissions since it would have a specific RPM and power band target. Diesels can be set up to run on biofuels or biofuel blends, or dual-fuel setups that use CNG or LP gas as primary fuel with only a few percent diesel as an ignition charge.

Drawbacks would be the weight of the diesel compared with a similarly powerful spark ignition engine. It would still need DEF and DPF to meet emissions, both of which add complexity and weight. Regen of the DPF and subsequent economy loss would be less of a problem, since designing the system to run with bursts of moderate to high load when recharging the battery would provide the exhaust temps needed for regen and discourage sooting in the first place.
 
Originally Posted By: VeryNoisyPoet
Will be interesting to see what others think about this. The vehicle could run off the electric motor but the diesel would kick in when the battery discharged below a certain point. It would work like a plug-in hybrid to allow zero emissions for shorter trips, and low emissions for longer highway cruising with a several hundred mile range.

Turbo diesels can be highly efficient, especially when used at more constant loads such as charging a battery and running the electric motor at cruising speed. It wouldn't have to deal with the challenges of prolonged idling, and could be tuned for very low emissions since it would have a specific RPM and power band target. Diesels can be set up to run on biofuels or biofuel blends, or dual-fuel setups that use CNG or LP gas as primary fuel with only a few percent diesel as an ignition charge.

Drawbacks would be the weight of the diesel compared with a similarly powerful spark ignition engine. It would still need DEF and DPF to meet emissions, both of which add complexity and weight. Regen of the DPF and subsequent economy loss would be less of a problem, since designing the system to run with bursts of moderate to high load when recharging the battery would provide the exhaust temps needed for regen and discourage sooting in the first place.


Yeah, something like that....:)
 
All of what’s been said, plus diesels are DI. You don’t see gasoline DI hybrids presumably because of the fuel dilution that would result if the engine was never at operating temperature for extended periods. Diesels May be even worse.
 
Interestingly, the thermal efficiency of gasoline engines in hybrids approaches that of the diesel. Toyota's most modern engines achieve 41% thermal efficiency. This is done through a variety of "tricks" (such as the modified Atkinson cycle) that are not easily employed on non hybrids (due to lack of torque and so on) . Remember, the electric motor(s) make up for lack of torque.

But I see no reason why a diesel electric hybrid could not be an excellent MPG machine.
 
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Originally Posted By: The Critic
Diesels take a long time to warm up. Until they are warmed up, the engine is inefficient.


If you are thinking diesels like the big old OTR machines, that's right.

If you are thinking modern engines that run on diesel, that's wrong.
 
Making a diesel pass current EPA emission levels renders it expensive and relatively less efficient.
Adding a battery/electric hybrid package might give some eye-popping mileage numbers but maybe no payback in the typical small vehicle lifetime, especially with the maintenance costs on these complex diesels. You can justify it on a transit bus because the payback over half a million miles or whatever the useful life is can be worthwhile.
 
The main thought of a small diesel was torque to turn the large generator. Maybe with some kind of fly wheel or gearing tricks?
 
Do you think a generator alone could keep a battery charged or increase range a great deal or don't they make enough juice?
 
Originally Posted By: ZZman
Do you think a generator alone could keep a battery charged or increase range a great deal or don't they make enough juice?


If the engine/generator combo is sized correctly, it can keep the battery charged. However, the amount of loss converting an engine's rotational power to electricity, then converting it to DC to charge the battery, then converting the DC battery power to AC then running the traction motor is a very lossy setup.

The Chevy Volt was originally conceived this way. In the end, they used a connection between the engine and the wheels, to improve overall MPG.
 
These out pull anything due to electric motor torque driven by diesel generators. It may be weight, need to start instantly, many factors why they stick to gas in cars. Like someone said busses are made as diesel hybrids. I think Toyota got their Prius hybrid ideas from GM's Allison division actually.

https://en.wikipedia.org/wiki/Electro-Motive_Diesel#/media/File:BN_9762_in_Yakima_Aug_71_NthCstHiRP.jpg
 
Originally Posted By: ZZman
Do you think a generator alone could keep a battery charged or increase range a great deal or don't they make enough juice?


Depends on the generator! The motor and generator are each maybe 90% efficient, so 0.9 x 0.9 = 0.81, or 81% efficient conversion from diesel engine crankshaft output to electric motor output. If the car is shaped like a Prius with low air resistance, it might only need 15 hp to cruise at highway speeds. So 15 hp / 0.81 = only 18.5 hp needed at the diesel engine to break even when cruising.

To run the motor, the generator's output would have to be 15 hp / 0.9 = 16.7 hp. One hp is 746 watts, so that would be 16.7 x 746 = watts 12,433 watts, or 12.43 kW. A large battery could easily soak up another 10+ kW when charging. So a 25 kW generator could charge the battery and cruise the car at the same time.

But for higher efficiency, the diesel can be connected to the wheels as well through a CVT transmission with two inputs and one output. This bypasses the 21% efficiency loss of mechanical to electric to mechanical conversion shown above and replaces it with just a few percent loss in the transmission. That way the electric motor can serve as the generator, saving weight and space. When the car is stopped while charging, the wheels are disconnected and the diesel keeps spinning the motor to charge the battery.
 
Originally Posted By: VeryNoisyPoet
Originally Posted By: ZZman
Do you think a generator alone could keep a battery charged or increase range a great deal or don't they make enough juice?


Depends on the generator! The motor and generator are each maybe 90% efficient, so 0.9 x 0.9 = 0.81, or 81% efficient conversion from diesel engine crankshaft output to electric motor output. If the car is shaped like a Prius with low air resistance, it might only need 15 hp to cruise at highway speeds. So 15 hp / 0.81 = only 18.5 hp needed at the diesel engine to break even when cruising.

To run the motor, the generator's output would have to be 15 hp / 0.9 = 16.7 hp. One hp is 746 watts, so that would be 16.7 x 746 = watts 12,433 watts, or 12.43 kW. A large battery could easily soak up another 10+ kW when charging. So a 25 kW generator could charge the battery and cruise the car at the same time.

But for higher efficiency, the diesel can be connected to the wheels as well through a CVT transmission with two inputs and one output. This bypasses the 21% efficiency loss of mechanical to electric to mechanical conversion shown above and replaces it with just a few percent loss in the transmission. That way the electric motor can serve as the generator, saving weight and space. When the car is stopped while charging, the wheels are disconnected and the diesel keeps spinning the motor to charge the battery.


Curious as to where you got all this interesting knowledge.
 
Originally Posted By: Cujet
Originally Posted By: ZZman
Do you think a generator alone could keep a battery charged or increase range a great deal or don't they make enough juice?


If the engine/generator combo is sized correctly, it can keep the battery charged. However, the amount of loss converting an engine's rotational power to electricity, then converting it to DC to charge the battery, then converting the DC battery power to AC then running the traction motor is a very lossy setup.

The Chevy Volt was originally conceived this way. In the end, they used a connection between the engine and the wheels, to improve overall MPG.


When I charge my Volt using Chargepoint, they show the kwhrs added. The amount used running on electric 100% is maybe about 10% less than what has to be replenished. If it uses 10, it takes about 11 to recharge. Maybe a little more. I like the Volt system, Honda has something similar with the Clarity. I don't know if that is considered very lossy or not.
 
Originally Posted By: ZZman
Curious as to where you got all this interesting knowledge.


I'm an electrical engineering student, and I've done some research on electric vehicles before. The rest was just simple math based on the laws of the universe and educated guessing.
 
Originally Posted By: VeryNoisyPoet

I'm an electrical engineering student, and I've done some research on electric vehicles before. The rest was just simple math based on the laws of the universe and educated guessing.


Cool. I like how you think. P. S: I didn't like math....
smile.gif
 
Originally Posted By: VeryNoisyPoet
But for higher efficiency, the diesel can be connected to the wheels as well through a CVT transmission with two inputs and one output. This bypasses the 21% efficiency loss of mechanical to electric to mechanical conversion shown above and replaces it with just a few percent loss in the transmission. That way the electric motor can serve as the generator, saving weight and space. When the car is stopped while charging, the wheels are disconnected and the diesel keeps spinning the motor to charge the battery.


VW had a concept that did that. However I'm not sure if it went anywhere. I don't think their idea was as good as yours, as I suspect Toyota had a patent in the way (pure speculation on my part).
 
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