Fuel Mileage - Diesel vs Gas

[WILDEBILL308]

Can't copy it but Gasbuddy says reg $1.68 and diesel at $2.15 at Buc-ee?s just north of me. ;D

 

[sightseers]

Can't copy it but Gasbuddy says reg $1.68 and diesel at $2.15 at Buc-ee?s just north of me. ;D

OMG ! .........regular gas is only $3.40 per gal here on the Left coast    Diesel is $4.00 per gal locally.

( and... there's another new 5.6 cent tax coming this July ) 

Welcome to California    :'(

 

[WILDEBILL308]

OMG ! .........regular gas is only $3.40 per gal here on the Left coast    Diesel is $4.00 per gal locally.

( and... there's another new 5.6 cent tax coming this July ) 

Welcome to California    :'(

To be fair there are more places selling reg in the $1.90 range and diesel in the $2.50 range.
Bill

 

[sightseers]

So...what was the fair part ?

 

[lynnmor]

( and... there's another new 5.6 cent tax coming this July ) 

Welcome to California    :'(

Oh No!  We in Pennsylvania will no longer be #1 in gas tax. 

 

[sightseers]

They say all these new taxes are necessary to make California better.

Legislators even raised the minimum wage up to $15.00 hr. to eliminate poverty. 

 

[Utclmjmpr]

Just another way to buy votes,, and when they can't buy them they import them.>>>D

 

[sightseers]

Just another way to buy votes,, and when they can't buy them they import them.>>>D

There is no need to buy or import votes......every night,  several hundred new democrats just walk into our state.    8)

 

[garyb1st]

This is a thread about Fuel Mileage.  I know it's a challenge guys, but can you guys leave politics out of the discussion. 

 

[thesameguy]

Xhp costs Ympg which ultimately costs $Z. Diesel vs. gas prices are just a calculation the oil companies run to maximize how much money they make. Until recently I had a diesel Suburban and watched fuel prices dance around wildly for no reason as all. Gas would go up, diesel down or vice versa. Gas wouldn't change, diesel would. Gasoline always moved linearly - a little up or down at a time, but diesel would move around like crazy. There were times when diesel was $0.50 less than gas on Monday and $0.50 more on Friday. Insane. Even with a "little" 37 gallon tank that hurt. Can't imagine it with a motorhome!

Tangentially, one thing I don't understand is why nobody does forced induction on gas engines on these big machines. The reason diesels make such insane torque figures is that they're all boosted. Sure, diesels make bigger torque simply on the basis on higher static compression, but what sends those numbers skyrocketing is the big turbos. If you throw a blower or a turbo on a big V8 you can net huge gains too. I've never understood why forced induction isn't a thing on motorhomes. I'm sure it's something I don't understand, but as the owner of 8 vehicles with forced induction and one motorhome without, I spend a lot of time creeping up grades scratching my head.

 

[Lou Schneider]

Tangentially, one thing I don't understand is why nobody does forced induction on gas engines on these big machines. The reason diesels make such insane torque figures is that they're all boosted. Sure, diesels make bigger torque simply on the basis on higher static compression, but what sends those numbers skyrocketing is the big turbos. If you throw a blower or a turbo on a big V8 you can net huge gains too. I've never understood why forced induction isn't a thing on motorhomes. I'm sure it's something I don't understand, but as the owner of 8 vehicles with forced induction and one motorhome without, I spend a lot of time creeping up grades scratching my head.

It takes horsepower to run a forced induction system, and that's power that consunes fuel but doesn't reach the road. What kind of MPG did you get on your supercharged cars running on a level road, I'll bet the same car running at the same speed with a normally aspirated engine would get better mileage.

Diesel and gas engines have one primary difference, a diesel engine has a wide open air intake all of the time because diesel fuel burns fine over a very wide range of air to fuel ratios.  You never hear of a diesel engine running too lean, so there's no reason to regulate the amount of air in the cylinder charge at lower power levels.  The air to fuel ratio doesn't matter until you inject enough fuel to consume all of the available oxygen in the cylinder.  That's when the diesel produces black smoke as unburned fuel spews out of the exhaust.

Forced induction increases the amount of oxygen in the cylinder charge, letting you inject more fuel and produce more power before reaching the smoke limit.

A gas engine needs a constant air to fuel ratio because gasoline burns best at the stoichiometric air to fuel ratio of 14.7:1. 

It uses a throttle plate to restrict the air intake to match the fuel delivery so you always have that 14.7:1 air to fuel ratio in the cylinder.  If you have more the optimum amount of air the engine runs lean, not enough air for the amount of fuel the engine runs rich.

When a gas engine is idling or producing less than full power, the throttle plate closes down, reducing the amount of air entering the cylinder to maintain the proper air to fuel ratio.  Unlike a diesel that keeps the air intake wide open all of the time.

Most of the time a gas engine uses less air than what's available from normal induction, i.e. the throttle plate is partially closed and the engine pulls several inches of vacuum in the intake manifold.  It doesn't make sense to waste power compressing air for forced induction if you're only going to use a throttle plate to restrict the amount of air reaching the cylinder.

The only place a forced induction system would help a gas engine is at wide open throttle.  Otherwise it's just a power drain lowering the engine's efficiency.

 

[garyb1st]

If I didn't have access to a library, I'd want Lou Schneider near by. 

 

[Lou Schneider]

Yeah, ask me the time and I'll tell you how to build a watch.   

 

[Joezeppy]

If I didn't have access to a library, I'd want Lou Schneider near by.

And a dictionary - "stoichiometric" - I had  to look that one up, LOL!

 

[sightseers]

OR....

how about replace that massively heavy diesel engine and transmission.... with a 400 horse 3400 rpm electric motor on a 2/1 ration differential and you are good to go 68 mph.

Then all the weight and room of the eng/trans, 100 gal fuel tank, radiator. filters oil tanks etc. ......can be swapped for L/I batteries.

then put an 106" wide by 40 ft. long solar panel on the roof, and wire up a 50 amp charge cord to it...

)
 

 

[thesameguy]

The only place a forced induction system would help a gas engine is at wide open throttle.  Otherwise it's just a power drain lowering the engine's efficiency.

That is utterly untrue. Forced induction can be configured to provide a benefit at a variety of engine load and speed indexes, and while in 1980 we didn't understand that, forced induction has come a VERY long way in the intervening 40 years. There are tradeoffs - sure - you don't get forced induction that's useful at both low and high engine speeds, but you can certainly configure for either or. That is the very foundation of modern production engines - small displacement engines with small, responsive turbos providing strong midrange performance similar to a larger engine. No, you don't get the full benefit of the smaller motor, but you do get the power delivery of the larger engine without paying the full economy penalty. How and where the forced induction helps has relatively little to do with throttle position and a whole heck of a lot to do with the displacement of the supercharger or the configuration of the turbo CHRA.

Yes, X hp will generally cost Y fuel, and whether you get your 500hp from a big ol' motor or a tiny motor with a blower you're going to get about the same economy BUT it's demonstrable that forced induction can overcome induction inefficiencies, help offset pumping losses, and improve combustion and that *could* be enough for a net win. Moreover, the parasitic loss for modern incarnations of these devices tends to be quite low. Low enough, I suppose, that Ford thinks an Ecoboost F150 is better than a 5.4l F150, so maybe take that under advisement.

Sure, you can concoct the scenario where forced induction is all bad (cruising Nebraska freeways) in the same way you can concoct a scenario where it's all good (climbing the Sierra Nevadas). The truth for most will lie somewhere in the middle. For me, living where I live and doing what I'd do, I'd gladly pay a parasitic loss penalty if it meant not creeping up the mountains at 35mph or wasting time behind a semi because I simply lack the power to pass safely. Of course, that's me - I don't spend a great deal of time in Nebraska.

 

[sightseers]

maybe motorhomes wouldn't need 500 h/p of smoke belching diesel power to get up a hill if they didn't have granite floors and counter tops with ceramic tile backsplashes on solid cherry wood cabinets with beveled glass doors.

take a luxury private jet..... somehow they can do lightweight opulence like this..

 

[WILDEBILL308]

maybe motorhomes wouldn't need 500 h/p of smoke belching diesel power if they didn't have granite floors and counter tops with ceramic tile backsplashes and solid cherry wood cabinets with beveled glass doors.

take a luxury private jet..... somehow they can do lightweight opulence like this..

You are to funny. What RV are you driving? What mileage are you getting? You should be aware that there are no new (post 2008)smoke belching diesels out there. They all have DPF filters and you don't have any exhaust smoke.
Yes some better diesel coaches are better built and do have some nice touches just like a luxury private jet.
If you think fuel cost are high on a "500 h/p of smoke belching diesel" Here are some of my figures on a fairley nice luxury private jet. Also maintenance is a little more per hour of operation. )
A Gulfstream's G650 burns right around 452.70 gallons of fuel per hour. At $5.00 a gallon, fuel is going to cost you $2,263.50 per hour. You can expect maintenance on a G650 to cost around $1,191.76 per hour of operation. $346.17 of that is for the airframe, and $845.59 is for the engine and APU.
But if the cost of fuel is to hi you can always go backpacking. ;D

Bill

 

[Larry N.]

take a luxury private jet..... somehow they can do lightweight opulence like this..

For how many millions of dollars to purchase? And how many thousands of dollars per hour operating costs? And how many years of training to fly it (plus the copilot)? And how much does insurance cost?

Ahhh... I see Bill has put in some good numbers. So I'll add that the G650 cost $65,000,000 in 2013. And I see there is a 2015 model available at a used price of $52,500,000, with 1775 TT on it (TT=Total Time).

A web site lists:
The total annual budget for flying a Gulfstream 650 private jet 200 hours per year is approximately $1,576,211
and
...which would equate to an average cost per mile of approximately $16.56 at 200 hours per year.

And here's a chart of operating costs:

Cost flying                                                                        200 hours/year           flying 400 hours/year
Direct Operating Costs (DOC)
Fuel Cost @ $4.40/gal Updated to Nat'l Avg Each Week $442,640                           $885,280
Maintenance                                                                 $105,846                           $211,692
Engine Overhaul                                                         $191,670                           $383,339
Misc Crew/Landing/Handling                                         $80,000                           $160,000
Miscellaneous Variable                                                 $30,000                           $60,000
Total Direct Operating Costs (DOC)                                 $850,156                           $1,700,312
Fixed Costs
Crew                                                                         $343,964                           $343,964
Crew Training                                                                 $112,270                           $112,270
Hangar                                                                         $106,236                           $106,236
Insurance                                                                         $56,987                           $56,987
Jet Management                                                         $78,000                           $78,000
Miscellaneous Fixed                                                         $28,598                           $28,598
Total Fixed Costs                                                         $726,056                           $726,056
Total Annual Budget                                                       $1,576,211                 $2,426,367

Slightly beyond my budget...

 

[sightseers]

America is still building luxury motorhomes like they used to build luxury cars back in the 60's...keep making them bigger and heavier.

Remember the 60's Cadillac Fleetwood, it was 25 feet long, it weighed 3 tons, massive beautifully decorated chromed steel bumpers,  with monster 472 cubic engine that got 7 mpg. (at best). 

Look at new luxury cars,  they are still comfortable, but lighter, faster, and get better millage....