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Marvin McConoughey
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Iron
Re: Diesel is a great opportunity, if - - -
Marvin McConoughey   2/25/2013 12:10:16 PM
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Relative fuel prices of diesel versus gasoline depends on several variables, including relative demand levels and refinery capacity.

Marvin McConoughey
User Rank
Iron
Re: Diesel is a great opportunity, if - - -
Marvin McConoughey   2/25/2013 12:06:12 PM
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Actually, General Motors had a great amount of diesel engine experience prior to designing the ill-fated diesel cars.  GM was the maker of GM diesel engines for trucks, boats, train locomotives, and small ships, as well as supplying numerous industrial customers. 

The problem was more likely one of excessive cost control efforts and insufficient development time.  The engines themselves were relatively simple and straight-forward in design. it is also possible that experienced GM diesel engine experts were not put in charge of the car diesel effort. 

There was nothing inherently wrong in basing the engine on a re-design of an existing block.  A review of the key dimensions--crankshaft main journal diameter, crankpin overlap, rod journal diameter, cylinder bore center distances relative to bore diameters, etc.; all suggest a quite robust design--especially in consideration of the meager power and torque output.  A friend bought one of the first Cadillacs with the diesel engine and, new,  it ran with remarkable smoothness and quieteness.  The quietness came from moderate RPM levels, an indirect fuel injection system, and Cadillac sound proofing efforts.

burgerc
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Iron
Re: Diesel is a great opportunity, if - - -
burgerc   2/25/2013 12:03:56 PM
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Visiting Europe from the US on a regular basis and having lived there and owned a diesel-powered passenger car, I am very familiar with diesels and their benefits.  I would like to drive a diesel, but with the current prices of diesel fuel vs. gasoline, diesels just don't make economic sense in this country.  I do not expect diesels to take off in the US if the diesel fuel prices don't become more favorable with respect to gasoline.

I was always under the impression that diesel fuel was less expensive to make since it is less refined than gasoline, but the current prices don't reflect that.  I suspect that people trying to "justify" the higher prices for diesel fuel are not completely unbiased and are really doing marketing.  In addition, politicians in many states have decided to tax diesel fuel higher than gasoline, which further hurts diesels.  This does not make sense during a time where fuel efficiency should be key.

 

Clemens

oldpumpguy
User Rank
Iron
Re: Diesel is a great opportunity, if - - -
oldpumpguy   2/25/2013 11:46:57 AM
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There are some very good points made here. The Chevy 350 diesel was a fiasco from the start when GM tried to "convert" a gasolene engine to diesel. Bearings, rods, head bolts...you name it, they just didn't have the design expertise. The fact that the Cruze diesel is a European design and in use there is a tremendous advantage. The engine looks robust.

I owned 3 VW diesels from the 70's and 80's that lasted forever ('78 Rabbet had 0ver 350,000 when traded for an '86 Jetta) and all returned 50+ MPG. The reason I got away from them was mainly because my commute changed from 106 miles to less than 6 miles a day and gas is about $.40/gallon cheaper.

I think the reason for the price differential has more to do with Federal fuel taxes to be sure the heavy trucks pay their fair share of road use taxes. Please correct me if I'm wrong, but I always understood the refining process to be easier and cheaper to make diesel than unleaded gas. After all, many in the Northern part of this country heat their homes with fuel oil which can be filtered and run in a diesel engine (illegal, by the way).  

Another point against automotive diesel is the gelling of diesel at temperatures below 25 F. Living in Pennsylvania, I wiould carry a 5 gallon can of kerosene in my trunk all winter. When filling the tank, I would add 1 gallon of kerosene first and then fill the tank (about 12 gallons) with diesel. This was the cheapest form of anti-gel possible and never bothered the engine or my fuel economy. The ONLY engine maintenance these three ever needed were oil & filter changes every 3 months (about every 6,500 miles).  

g-whiz
User Rank
Gold
California hates Diesel owners
g-whiz   2/25/2013 11:35:18 AM
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California continues to penalize Diesel owners. I drive an '84 Mercedes and a Ford PowerStroke. Diesel fuel is consistently more expensive than premium gasoline, mostly because CA insists on taxing at a much higher rate than gasoline. In 2004, Sales tax prepayments were 0.09/gal for gasoline and 0.07/gal for Diesel. Today, it's less for gas at 0.07/gal but has soared to 0.29/gal for Diesel.  CA has also now mandated smog checks for diesels even though there is no measuring equipment. The "check" takes about 5 minutes and consists of a visual verification that you have not modified the intake or exhaust system and costs $80.

Several years ago, I had the pleasure of renting and driving a diesel powered Ford Focus station wagon while in France on business for 3 weeks. I would have purchased that vehicle in a heartbeat in the US if it was available. Once it got off idle, you'd never know it was a diesel. Plenty of power and real stingy on fuel.

Bob Salter
User Rank
Iron
Re: Diesel is a great opportunity, if - - -
Bob Salter   2/25/2013 11:33:35 AM
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Every Mechanical Engineer should know that engine torque is what moves motor vehicles. Horsepower is the product of torque and RPM, and is important for those looking for high performance. High horsepower means you can keep your performance vehicle in a lower gear longer when accelerating in order to take advantage of more torque multiplication. From years of studying advertised engine performance specifications, it can be seen that higher compression ratios result in higher peak torque values, usually in engines for performance vehicles. Therefore, Diesel should make much higher torque because of much higher compression ratio.

Keep in mind that there is "mechanical" compression ratio, which is a comparison of cylinder volumes and "thermodynamic" compression ratio which is a comparison of actual cylinder pressure at TDC and atmospheric pressure. The ability of Diesel and Otto engines to breathe in more air at higher RPMs, "volumetric efficiency", is what allows the torque and horsepower curves to fall off at higher RPMs.

Two important things I remember from Thermodynamics 101 are: 1. The way to increase power output from any internal combustion engine is to flow more air and heat it up higher; 2. The higher the engine's thermodynamic compression ratio, the higher its efficiency, exponentially.

Does Low Sulfur Diesel fuel also provide a torque boost from a 12% higher heat value, 129.5 BTU/gal. versus 116 BTU per gal.? I guess you actually do get what you're paying for as Diesel fuel where I live costs 12% more than regular gasoline. Its heating value in BTU/lb is slightly less than gasoline, and in combustion, it's the respective masses of air and fuel that are used for calculations of fuel mixtures. But, we do buy both fuels by the gallon, and using vehicle miles per gallon - MPG- we can easily calculate fuel cost per mile.

If one is trying to calculate total engine operating expense between the two engines, maintenance needs to be considered? For me, the greatest concern would be how much does it cost to have Diesel fuel pump replaced. Also, how much does a newer direct injection gasoline fuel pump cost versus a convention 60 PSI fuel pump?

 

astalevista
User Rank
Iron
Re: Diesel is a great opportunity, if - - -
astalevista   2/25/2013 11:31:21 AM
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Diesel is very well suited to US market. The only weak point of diesels is lower power @ same engine volume due to lower max RPMs. But from driving experience  it only matters when passing somebody @ 120 MPH - impossible on US roads. Always rent diesels when in Europe; all of them are 2.0L (Europe tax larger engines heavily), turbos for larger power. GM (Opel) are the worst of all (VW, BMW, FIAT, RENAULT): very narrow turbo RPM range (3000-4000) so turbo is practically useless.

Bonzoboy
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Iron
Re: Diesel is a great opportunity, if - - -
Bonzoboy   2/25/2013 10:46:49 AM
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But I don't think Germany tries to reach the same low emission levels required here in the US.  We'd be far better off with more, clean, diesels on the road.  We could probably shave 1-3% of our total liquid fuels consumption.

Battar
User Rank
Platinum
Price?
Battar   2/25/2013 10:44:42 AM
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Diesel more expensive than gasoline to produce? Never heard that song sung before. I'd always assumed that the reason ships (even giant container ships), locomotives, commercial vehicles, buses, military armoured vehicles, standby generators, stationary power generators etc all use diesel engines is because the fuel is cheaper and the engine more efficient.

In my country, diesel is more heavily taxed than gasoline, the reasoning being that the goverment will claim the same tax figure even if your engine is more fuel efficient. Commercial users get a tax rebate.

If you want fuel efficency, diesel is the way to go.

kodaiflow
User Rank
Bronze
Re: Diesel is a great opportunity, if - - -
kodaiflow   2/25/2013 10:03:10 AM
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California and Mass essentially banned diesel cycle, so car companies don't want to put a product on the road that can't enter the largest market in the country.  The EU has lower standards for NOX.  The car companies have now developed CATs that can lower the NOX and have particulate traps to reduce those emmisions so they can be sold in CA. 

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