[bwilson4web]

Originally Posted by Christ

Apples to Apples, the gasoline engine currently in use by the prius also doesn't have regenerative braking. The electric motor stored in the housing on the back of the gasser's block is what creates that function.

We call that "gasser's block" the transaxle but I'll adopt your curious term, "the back of the gasser's block."

Originally Posted by Christ

. . .
Diesels aren't inefficient at low power, they're inefficient at low LOAD... same thing with gas engines. . . .

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 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.

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.)

So what do you call a diesel transmission or transaxle, some sort of "the back of the diesel's block?"

Originally Posted by Christ

. . . Diesels can be run as low power as you want them, provided the engine's dynamic displacement compares to the power being created.

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.'

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.

Originally Posted by Christ

. . .(This is where EGR comes into play.)

At high power settings, the 1.8 Liter Prius engine uses excess EGR flow to fill the combustion chambers, which decreases dynamic displacement, keeping BSFC higher by lowering cylinder temps.

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:




I didn't see them using "dynamic displacement" to explain what is going on. Is that some sort of diesel term?

Originally Posted by Christ

. . . Diesels don't have difficulty handling start/stop operation as much as people like to think. Talk to a farmer some day, who runs diesel tractors.

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.

Originally Posted by Christ

. . . As far as being heavy, compare the power to weight ratio (and potential power to weight) of a diesel to a gasser... they're about the same. The diesel has the potential to produce the same horsepower at the same weight (meaning smaller displacement) than a gasser.

<sigh>Yes of course, the 'potential' is always there.

Bob Wilson