Gas, Diesel, 6-speeds

[r carl]

So can we expect 12 to 15 mpg with a new diesel and 9 to 12 with a new gasser while towing?
If we go out to buy a new TV, is diesels only in pickups? I would think a suburban type TV would appeal to many folks.

[AirsDream]

A few comments:

First, my experience is that diesels take a looooong time to break in but also last a long time. One of mine, now at 190,000 miles did not peak out on fuel mileage until after 65,000 miles. Today it still gets the same mileage as it did at 65,000, and uses no oil. Lots of folks report 400,000 miles or more beofre a rebuild.

Second, fuel mileage will always be better with a diesel due to the higher btu content of the fuel, but that varies depending upon summer / winter fuel blend. And it's not my reason for buying diesels ... the fuel's higher priced per gallon, maintenance can be higher, etc. I buy 'em because a.) the enormous torque advantage lets me tow whatever I want wherever I want; b.) the long-term engine durability; and c.) the extra chassis durability that comes with a 3/4 tonner. I don't really need the chassis strength for towing my little Airstream most of the time. But the Allison xmission and the much larger brakes, ring gear, etc. mean it's less likely to crap out on me at a young age.

Third, don't sell gassers short. I've got a friend who drives a LOT in 1/2 ton pickups (usually not towing) and he NEVER trades his pickups in until they've got over 200,000 miles on the clock. They are very durable these days.

Fourth, fuel mileage towing is highly speed, terrain, and wind dependent. My best trip towing ever with my '08 Duramax (500 miles with one fuel stop) averaged 15.6 mpg. That was at about 65 mph, over pretty flat terrain, with a slight tailwind most of the way. My overall average expressway speed when towing is a bit faster than that and averages 12.4. Slow down to whatever speed is about max torque on the tachometer, travel on flat land, go downwind, and all is good. Head for the mountains, speed up and tow into a snow squall, and it gets bad. No matter what the motive power source.

[dznf0g]

Originally Posted by AirsDream

A few comments:

First, my experience is that diesels take a looooong time to break in but also last a long time. One of mine, now at 190,000 miles did not peak out on fuel mileage until after 65,000 miles. Today it still gets the same mileage as it did at 65,000, and uses no oil. Lots of folks report 400,000 miles or more beofre a rebuild.

Second, fuel mileage will always be better with a diesel due to the higher btu content of the fuel, but that varies depending upon summer / winter fuel blend. And it's not my reason for buying diesels ... the fuel's higher priced per gallon, maintenance can be higher, etc. I buy 'em because a.) the enormous torque advantage lets me tow whatever I want wherever I want; b.) the long-term engine durability; and c.) the extra chassis durability that comes with a 3/4 tonner. I don't really need the chassis strength for towing my little Airstream most of the time. But the Allison xmission and the much larger brakes, ring gear, etc. mean it's less likely to crap out on me at a young age.

Third, don't sell gassers short. I've got a friend who drives a LOT in 1/2 ton pickups (usually not towing) and he NEVER trades his pickups in until they've got over 200,000 miles on the clock. They are very durable these days.

Fourth, fuel mileage towing is highly speed, terrain, and wind dependent. My best trip towing ever with my '08 Duramax (500 miles with one fuel stop) averaged 15.6 mpg. That was at about 65 mph, over pretty flat terrain, with a slight tailwind most of the way. My overall average expressway speed when towing is a bit faster than that and averages 12.4. Slow down to whatever speed is about max torque on the tachometer, travel on flat land, go downwind, and all is good. Head for the mountains, speed up and tow into a snow squall, and it gets bad. No matter what the motive power source.

Most accurate post of the day award goes to you!

[JFScheck]

Originally Posted by vswingfield

That sounds an awful lot like calling it a hybrid to me.

Read it in context...

And why am I even replying to this?

This Horse Has Been Beat to Glue - time to move on...

[vswingfield]

Originally Posted by JFScheck

Read it in context...

And why am I even replying to this?

This Horse Has Been Beat to Glue - time to move on...

Originally Posted by JFScheck

How about a Ford V-6 with the "Hybrid Technology" as I like to say - or in Ford speak "Eco-Boost"...

For your 25 footer & F-150 or 1500 combo - that could be a great choice!

Of course - if they came out with a nice V-6 diesel (like my wonderful TDI) I would be all over that...

Sorry, still sounds like you're calling it a hybrid to me.

[tpi]

What I think his point was the ecoboost is somewhat a hybrid between gas and diesel engines.

I think the direct injection is key. It allows higher compression ratio and more boost without detonation. The fuel can be injected late in the compression stroke allowing normal combustion to occur before unwanted detonation. In my opinion it is direct injection which allows so much turbo boost at low RPM giving the engine the very high torque at less than 2K RPM.

When under high manifold pressure, gas engine efficiency is not all that terrible. True the fuel has less heat content. But the ecoboost attempts to avoid the lazy combustion and pumping loss of a gas engine operating at high manifold vacuum.
See page 11 of this PDF (also in the PDF some neat pics of diesel combustion):
http://files.nequam.se/greenCarLecture.pdf

[vswingfield]

Originally Posted by tpi

What I think his point was the ecoboost is somewhat a hybrid between gas and diesel engines.

I think the direct injection is key. It allows higher compression ratio and more boost without detonation. The fuel can be injected late in the compression stroke allowing normal combustion to occur before unwanted detonation. In my opinion it is direct injection which allows so much turbo boost at low RPM giving the engine the very high torque at less than 2K RPM.

OK. I will consider that.

I guess that the term "hybrid" has gotten some baggage from the gas/electric combos and I just went down the wrong path.

[DKB_SATX]

Originally Posted by tpi

What I think his point was the ecoboost is somewhat a hybrid between gas and diesel engines.

I think the direct injection is key. It allows higher compression ratio and more boost without detonation. The fuel can be injected late in the compression stroke allowing normal combustion to occur before unwanted detonation. In my opinion it is direct injection which allows so much turbo boost at low RPM giving the engine the very high torque at less than 2K RPM.

When under high manifold pressure, gas engine efficiency is not all that terrible. True the fuel has less heat content. But the ecoboost attempts to avoid the lazy combustion and pumping loss of a gas engine operating at high manifold vacuum.
See page 11 of this PDF (also in the PDF some neat pics of diesel combustion):
http://files.nequam.se/greenCarLecture.pdf

On the drawing boards, in the test labs and in a few test mules, there's a true cross between Diesel- and Otto-cycle engines, that can burn gasoline (or other more-volatile fuels) and have spark plugs for startup and rich-mixture operation, and transition to compression-ignition under cruise conditions.

I think we're just now getting to the point where digital engine control systems are reliable enough and fast enough to make it work. I know that GM has had engines like this running in test conditions for several years, but no one is putting it into production.

[tpi]

I think we're just now getting to the point where digital engine control systems are reliable enough and fast enough to make it work. I know that GM has had engines like this running in test conditions for several years, but no one is putting it into production.

So far I think the hangup has been emissions, particularly NOX, for running leaner than 14.7 to 1 mixture.

What I wonder is if eventually urea injection will be used in lean burn or stratified charge gas engines. Its already off the shelf for diesels.

Theoretically they can at least run the current 14.7 gas engines nearly unthrottled, at least when towing, using all the OD ratios in the transmission. Think of all the possible control points you have in the ecoboost with the computer controlling the transmission, wastegate, perhaps other parameters of turbo operations, injection and ign timing, and the throttle. There could be a time, if it isn't now, where the gas pedal in the car and the actual throttle could be doing very different things.

[dznf0g]

Originally Posted by tpi

What I think his point was the ecoboost is somewhat a hybrid between gas and diesel engines.

I think the direct injection is key. It allows higher compression ratio and more boost without detonation. The fuel can be injected late in the compression stroke allowing normal combustion to occur before unwanted detonation. In my opinion it is direct injection which allows so much turbo boost at low RPM giving the engine the very high torque at less than 2K RPM.

When under high manifold pressure, gas engine efficiency is not all that terrible. True the fuel has less heat content. But the ecoboost attempts to avoid the lazy combustion and pumping loss of a gas engine operating at high manifold vacuum.
See page 11 of this PDF (also in the PDF some neat pics of diesel combustion):
http://files.nequam.se/greenCarLecture.pdf

DI does not a hybrid between gas and diesel make! DI is all over the place and has been for several years now...in 4 cyl. and 6 cyl from GM, Ford, and others. The only true gas/diesel "hybrid" (and tha's an incorrect term, but OK) is called HCCI. They are not out yet, but will be before the 2016 CAFE regs kick in. It is Homogeneous Compression Combustion Ignition. They will also be DI, but at idle and under very light loads they will be compression ignited, not spark ignited. This allows for very lean gasoline mixtures to be used, without knocking, or high NOx emissions, not to mention burning valves and piston heads up.

[DKB_SATX]

Originally Posted by dznf0g

DI does not a hybrid between gas and diesel make! DI is all over the place and has been for several years now...in 4 cyl. and 6 cyl from GM, Ford, and others. The only true gas/diesel "hybrid" (and tha's an incorrect term, but OK) is called HCCI. They are not out yet, but will be before the 2016 CAFE regs kick in. It is Homogeneous Compression Combustion Ignition. They will also be DI, but at idle and under very light loads they will be compression ignited, not spark ignited. This allows for very lean gasoline mixtures to be used, without knocking, or high NOx emissions, not to mention burning valves and piston heads up.

HCCI is not likely to be DI, because the "HC" is "Homogeneous Charge" and DI gives you a stratified charge unless you go for a VERY early injection timing, and then you give up the advantages of DI and might as well have gone port-injection or throttle-body injection and saved money on hardware. They'll probably do some twist on it (SCCI?) to use the new DI tech if there's an advantage to it.

[dznf0g]

Originally Posted by DKB_SATX

HCCI is not likely to be DI, because the "HC" is "Homogeneous Charge" and DI gives you a stratified charge unless you go for a VERY early injection timing, and then you give up the advantages of DI and might as well have gone port-injection or throttle-body injection and saved money on hardware. They'll probably do some twist on it (SCCI?) to use the new DI tech if there's an advantage to it.

My understanding is it will be DI since it operates like a regular fuel injected gasser most of the time. I haven't been formally trained on it yet, but have spoken to some engineers and have very vague powerpoint presentation materials. It will operate in two very distinct and separate modes. Perhaps the DI injectors will shut off and some more stratfied injector will take over, I do not know, but the whole purpose of this technology is to gain incremental fuel economy gains. Why give up the 10 - 15% gain which DI provides for the 5 - 10% that HCCI is projected to provide. Guess we'll have to wait and see.