BMW's Diesel Plug-In Hybrid: 63 mpg, Faster Than an M3

Gearlog ^ | November 23, 2009 | Bill Howard

[Colorado Cowgirl]

It appears most cars don’t match up like we would like them to. It’s never a apples to apples comparison. I would love to match a VW TDI diesel with a similar VW gasoline engine. No such luck. But in 3/4 and 1 ton versions of trucks. The comparison is there. I have a 1996 3/4 ton Dodge Ram 4x4 with a Turbo Diesel 359 CI engine, it weighs 7000 pounds. I average 19 to 20 MPG. A 1996 Dodge Ram 4x4 gas burner 360 CI engine will only get 10 to 12 MPG and most only get 8 to 10 MPG. Even if it got 14 MPG. I still get 40% better MPG.

[Jeff Chandler]

a simple Bicycle chain won hands down for power transfer.

Perhaps, but with hydraulics a smaller power plant can be used because the energy can be accumulated for power bursts and deceleration energy can be scavenged. It does everything electric hybrids attempts to do but far more efficiently and without the negatives of batteries.

[Red Badger]

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[ConservativeMind]

Doesn’t the fact that diesel engines run “cold” mean they lose less energy to waste heat?

[thackney]

Diesels Run Cold?

I tried to research this farther but didn’t find the data I expected to easily put my hands upon.

I think that from what I found diesel are more efficient but I believe the amount of difference is smaller than some here have suggested.

Unfortunately too many time constraints for me right now to find and document asI would like.

I’ll add it to the growing list of things I should learn.

[thackney]

I wanted to thank you for the info.

I still doubt the 40% as typical but I found it more difficult than expected to find basic data from the same vehicle with gasoline versus diesel engine.

I would think with options of both available it should be out there on the web somewhere.

Diesel is more efficient. Thanks for the exchange.

[EyeGuy]

“Not enough room to haul my stuff.”

####

Indeed.

Not even close.

But it is oh so “smart”, and by implication you are “smart” simply for driving one.

[ConservativeMind]

“Diesel engines generally achieve greater fuel efficiency than petrol (gasoline) engines. Diesel engines have energy efficiency of 45% and petrol engines of 30%.[3] That is one of the reasons why diesels have better fuel efficiency than equivalent petrol cars. A common margin is 40% more miles per gallon for an efficient turbodiesel. For example, the current model Skoda Octavia, using Volkswagen engines, has a combined European fuel efficiency of 38.2 mpg for the 102 bhp (76 kW) petrol engine and 53.3 mpg for the 105 bhp (78 kW) — and heavier — diesel engine. The higher compression ratio is helpful in raising the energy efficiency, but diesel fuel also contains approximately 10-20% more energy per unit volume than gasoline which contributes to the reduced fuel consumption for a given power output.[4]”

http://en.wikipedia.org/wiki/Fuel_efficiency

It appears that the average diesel engine is 50% (45% vs. 30%) more efficient in generating power output from a US gallon of fuel than can an average gasoline engine. The BTU content is a small amount of this (diesel has 5%-15% more BTUs/gallon (bio vs. normal) than gasoline). The rest comes from the effect of a high compression ratio.

Add to this that diesel is able to provide much more torque at the low end RPMs (which everyone must always use), it looks even better.

However, one must subtract out that the diesel engine is, itself, rather more heavy than a gas engine. This reduces our practical power output in the above mention, but it does not reduce the actual amount of real work it performs from a gallon of fuel (moving a heavy engine is still work performed, even if you'd rather not move a heavy engine).

[ejonesie22]

What year is it?

M3s are fun little zoom cars...

[RightOnTheLeftCoast]

"Looks become secondary when you drive the 1-series."

Maybe after your brain stops aching from whacking your head on the roof edge when getting in and out. What were they thinking??

[thackney]

I appreciated the effort but I don’t consider wikpedia anything beyond an opinion and not actual data.

It is useful to gain understanding and I often find the outside links helpful.

But don’t confuse wikpedia as confirmed data.

[ConservativeMind]

Okay, on to the source:

“Diesel engines are already more
efficient than gasoline engines (45
percent versus 30 percent), and further
advances are possible (to 55-63
percent).

http://www1.eere.e”nergy.gov/vehiclesandfuels/pdfs/basics/jtb_diesel_engine.pdf

1 gallon of gasoline = 124,000 Btu (based on U.S. consumption, 2008)
1 gallon of diesel fuel = 139,000 Btu

http://tonto.eia.doe.gov/energyexplained/index.cfm?page=about_energy_units

I know you may have a problem with governmental sources, but that's about as good as I can quickly find.

[ConservativeMind]

That first link shouldn’t have that quote in it. Here it is again, corrected.

http://www1.eere.energy.gov/vehiclesandfuels/pdfs/basics/jtb_diesel_engine.pdf

[thackney]

I know you may have a problem with governmental sources, but that's about as good as I can quickly find.

Mostly they are good. EERE can tend to be biased towards alternative fuels but rarely something like diesel. And EIA is an excellent source, in my opinion.

Thank you for that.

[thackney]

I finally found the type of comparison I was looking for in comparison of diesel versus gasoline.

http://www.fueleconomy.gov/feg/FEG2010.pdf

The results are, in my opinion, conclusive of an efficiency advantage of diesel, but conflicted in terms of just how much.

The Volkswagen Golf numbers are right in line with both of your expectations, 40~50%.

The Mercedes is more like I thought I would see, 20~25% advantage to diesel.

Audi was 31~39% advantage diesel. BMW was 24~27%. Volkswagen Touareg was 29~32%. Volkswagen Jetta was 25~31%.

Altogether, they average 31%. Heavier trucks are not included, I wish the rated the 1 ton trucks the same way.

[thackney]

Also note, that “pure” gasoline is not what the EPA allows us to use in the USA. When they did sample testing, they got about 113,500 BTU/gallon for convectional gasoline. This gives diesel about a 22% advantage in energy per gallon.

http://www.epa.gov/oms/rfgecon.htm

The difference is greater still for Reformulated Gasoline used in many different areas. Both Ethanol and MTBE lower the energy but ethanol is worse.

[thackney]

convectional = conventional

[ConservativeMind]

But also note that biodiesel has a lower BTU rating than that given by the government, and that the numbers collected by the US government on total efficiency of diesel vs. gas engines were possibly done prior to mandates for ethanol gasoline.

In addition, even at the “worst case” of a 22% fuel energy benefit for diesel, that no where accounts for the additional 28% efficiency provided by said diesel engines over that of gas engines.

[Gay State Conservative]

Now do you believe?

Having just bought my first diesel a couple of months ago (a BMW 335d) I'm now a *major* believer.I get 43 mpg at a steady 65mph (unlike many Bimmer owners,I'm not a hot-rodder) and yet,when needed,the thing's a rocketship (passing,merging onto an Interstate,etc).The upcoming winter will be my first one with a diesel so I'm a bit wary of being stranded by fuel gelling but I guess we'll just have to see what happens.