Originally Posted by bwilson4web
We call that "gasser's block" the transaxle but I'll adopt your curious term, "the back of the gasser's block."
I mistakenly thought that the e-motor was placed in a housing between the transaxle and engine, thus being "on the back of the gasser's block" I'm well aware of the terminology associated with automotive engineering, thank you.
Both a diesel and a gas engine require a minimum amount of fuel burn to run at idle. Call this the 'heartbeat' or minimum operating fuel burn rate. If the engine, diesel or gas, requires double that amount of fuel to provide the "low LOAD," the efficiency has increased over idle, a little bit. But the Prius plays a trick with its "the back of the gasser's block" (called a transaxle.)
The diesel is always fundamentally operating under less load than any throttle controlled gas engine, due to the lack of intake restriction, making for less pumping losses. Frictional losses are slightly increased due to cylinder temperature differences between the diesel and (significantly cooler) gasser.
The Prius produces much more energy than is needed by the load so the engine 'hearbeat' or minimum idle burn rate is a small fraction of the total fuel burn. The energy in excess of what the vehicle needs is converted into electrical energy stored in the battery. Then soon as there is enough energy in the battery, the Prius gas engine shuts down and the stored energy in the battery is used to move the car. Thus a larger portion of the Atkinson cycle energy is ultimately used for vehicle power compared to the diesel that is running in a power range that a significant portion of its energy just meets the 'idle power' need.
What does this have to do with any reason that a diesel couldn't be used in the same hybrid system? Remember, way back there, when noone ever said that it should be diesel only? Yeah, I actually pointed it out a few posts back... that it could still retain the hybrid system, and still be more efficient than the gasser version. I don't suppose you've ever seen that the most fuel efficient Prius runs actually involved not using the e-motor at all...
In contrast, the diesel-only car at "low LOAD" continues to pay a significant portion of its fuel burn just to keep the engine running. Without an integrated "the back of the gasser's block" (called a transaxle,) the diesel performs poorly at "low LOAD" (aka., city driving.)
Prove it.
By the way, Low Load situations DON'T include city driving. City driving is considered variable high-load driving, since you're always either accelerating or braking (or, in the case of many here, coasting.) Low load driving is on the highway, maintaining a steady speed, where the horsepower requirement to cruise is a low comparison to the potential output of the engine at the given engine speed.
So what do you call a diesel transmission or transaxle, some sort of "the back of the diesel's block?"
Assuming that there was an e-motor attached to a housing behind the diesel engine, I would have used the same terminology. Thank you for attempting to make light of something you obviously didn't understand.
The problem is the minimum energy needed at idle remains a significant portion of the energy burned just to keep the engine turning over, the 'idle fuel burn.'
Except the quite obvious fact that a diesel, while possibly burning more fuel to idle (although highly unlikely, given the nature of diesel engines), can also idle significantly lower than the average gas engine, and do so reliably, thus cutting that fuel consumption. While the consumption per revolution might be higher, the number of revolutions per minute and thusly, fuel used per minute will still be lower.
Now part of the internal friction comes from the piston rings having to seal the gas pressure. On the compression stroke, the diesel goes from 20-to-1 whereas the Atkinson engine Prius goes from 8-to-1. The Prius has a lower pressure load on the rings than the diesel. Then comes the power stroke and both are dealing with similar pressures and friction.
That may be, but higher compression engines extract more energy from each revolution as well.
All I know is what I've read in SAE 2009-01-1061, "Development of New 1.8-Liter Engine for Hybrid Vehicles" Kawmoto, Naiki, Kawai, Shikida, and Tomatsuri, Toyota Motor Corporation:
[Images Omitted]
I didn't see them using "dynamic displacement" to explain what is going on. Is that some sort of diesel term?
No, it's an engine design term. Static displacement is a measure of an engine's available capacity. Dynamic displacement accounts for volumetric efficiency. Volumetric efficiency is a comparison of actual drawn volume versus Static Displacement, expressed as a percent. For example - A 1 liter single cylinder engine running at 75% VE is drawing/expelling .75 liters per intake stroke, or .375 liters per revolution. Volumetric Efficiency is based on air/fuel mix, regardless of air/fuel ratio. Adding EGR flow to the cylinder during operation changes the Dynamic Displacement Availability, but does not affect VE when expressed as a percent of ACTUAL available capacity. Understand now?
Usually it takes a little more torque and energy to turn a crank against a 20-to-1 compression stroke than an 8-to-1 compression stroke for identical displacement engines. Having cranked a Model A Ford before, I remember the effort needed.
Sure, it does. That's obvious. The extra weight of the internal components also requires more work to move in a diesel. It also takes more energy to pump diesel fuel at the high pressures necessary for proper operation in a diesel engine. Petro-Diesel fuel also contains ~15% more energy per unit than gasoline, and Diesel engines are better at extracting energy with less wasted energy than gasoline engines.
<sigh>Yes of course, the 'potential' is always there.
Potential, in this case, isn't the unrealized kind that you seem to think it is.
Bob Wilson
Christ Pettitt. Nice to meet you.
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