clett,

I would like to see your source for the mean efficiencies of gasoline and diesel engines.

I have found in general that the well-to-pump emissions of diesel and gasoline are roughly equivalent. What makes you think it is so much lower for diesel?

clett,

I will explain to you why I would like to know how you got the mean efficiencies of gasoline and diesel.

A real world example:

Volkswagen Golf 1.4 TSI 90 kW average consumption 6.3 l/100 km

Volkswagen Golf 1.9 TDI 77 kW average consumption 5.1 l/100 km.

The diesel is heavier, but the gasoline version has better performance. Let's assume these two diffences have a minor influence on fuel consumption and cancel each other out.

The consumption of the gasoline Golf is 24% higher, but half of that can be attributed to the lower energy content of a litre of gasoline, leaving an average efficiency that is around 12% worse than the diesel version.

According to your data, the gasoline version should consume 40/25 = 60% more on an energy equivalent basis or 66% more on a litre for litre basis. I have never encountered such large diffences. Neither in rated fuel consumption, nor in real world fuel consumption.

If you examine other cars you will find roughtly the same difference.

Diesel hybrid buses they are introducing here in San Francisco are fantastic. I have no idea about efficiency but they are so much quieter. Half the buses here run on electricity via the overhead lines but even progressive/"Al Gore is my hero"/NIMBY San Francisco fights tooth and nail when they want to expand those lines into new neighborhoods. I guess when you get right down to it aesthetics are really more important to self proclaimed progressives than environmentalism.

No one has mentioned natural gas hybrid as a solution. But then I'm from the midwest and I don't know the availability of natural gas in California. Please enlighten me.

Anne,
Your patience is admirable.

Once again the CONSPIRACY theorists climb out of the closet, or from under the rock. GM tore up the tracks.
Please.

This is a phony study. The Transit community publishes over all transit system mileage statistics. It knows that the the average mileage of diesel buses is below 2 miles per gallon and closer to 1.5 mpg on average. Include idling, and HVAC losses. There are not yet enough hybrids to affect that mileage figure much.

Rolling resistance is reduced with rail. But it hardly offsets, the much heavier trolley vehicles. They probably weigh in at three time as massive. Moving more mass and the resistance losses in catenary systems, balance rubber rolling losses.

T2B5 diesel hybrids, can be afforded in the price of a bus. Trolleys are an earlier and more primitive technology. But neither save much fuel per trip. How full, for every inch of the the route, must a bus or trolley be to merely break even?

At 1.5 mpg? At 2 mpg? at 3 mpg? Then add the drivers cost. Then add the capital costs.

There are no private transit systems. There is a reason for why that is. And its not a CONSPIRACY.

@ Anne,

Should note at this point that the 1.4 TSI gasoline engine is VW's most efficient gasoline engine but is unavailable in North America (too bad, it's a nice unit). The base gas engine that is available here, the plain ordinary 2.5, uses quite a bit more fuel than the 1.4 TSI. Can't use the euro ratings since the 2.5 isn't available there, but one can use the Transport Canada ratings for 2006, the last year for TDI availability (2009 ratings aren't out yet).

Jetta 2.5 gas engine 5-sp manual 10.8 L/100 km city 7.2 L/100 km highway.
Jetta 1.9 TDI 5-sp manual 6.6 L/100 km city 5.2 L/100 km highway

For this situation, the gasoline version consumes 64% more city, 38% more highway.

The high performance 2.0 TFSI actually has a little better ratings than the 2.5 base gas engine, BUT, it requires premium fuel, and it costs more, and the manual transmission is a 6-speed, so it doesn't directly correspond.

It has to be kept in mind also, that the 1.4 TSI engine requires premium gasoline, and costs more than the base gasoline engine.

How does this relate to the original topic? The Ford V10 engine that they used in that bus is a lot closer in "level of tech" to VW's base gasoline engine, than it is to VW's 1.4 TSI. (No turbo, no direct injection.)

3.35 mpg is too low for a hybrid bus, considering that a bigger 40-tonne diesel tractor-trailer (80,000 lbs) can get 5-6 mpg hwy cruising. 3.5 mpg for a diesel bus is about right, because of frequent stopping and idling.
A gasoline-electric hybrid ought to be at least capable of 5-6 mpg overall driving.

The problem here is due to the serial hybrid setup, which robs efficiency. A bus drive train operates under heavy duty-cycle of frequent accelerating and breaking, which puts motor and generator efficiency down to probably 70-80% range realistically. Multiplying motor x generator x power inverter efficiencies: .75 x .75 x .8 = .45, or 45%-efficient transmission-drive train system. The 400-Volt AC system is too low for this size of vehicle, forcing too high currents, hence more resistive loss. Even the much-smaller Prius has 500-volt power train system. Over thousands of volts should be used in this size of vehicle for higher efficiency. Of course, this poor efficiency is made up for by the lack of idling and regenerative braking, allowing it to slightly improve efficiency over that of a pure diesel bus. Installing larger motors and generator into this serial hybrid bus will improve overall efficiency but the extra cost and weight may not be acceptable to fleet purchaser.

A serial-parallel architecture like GM's dual-mode or Toyota's HSD will be much more efficient, since a significant percentage of engine power will be transmitted mechanically to the drive train at ~95% efficiency.

Clett,
An optimized gasoline engine should have a peak efficiency at around 32%. An Atkinson-cycle gasoline engine should achieve 37-40% peak efficiency. A large diesel engine should be capable of 42-45% peak efficiency.

Regarding thermal efficiencies, although a good gasoline Otto cycle can PEAK at 30%, and the Prius "Atkinson/Miller" cycle at 35%, these figures are only attained under quite particular driving conditions (depending on load and rpm etc).

At low load, or at idle, gasoline engines are MUCH less efficient than their peak rated thermal efficiency. I was probably being generous by guessing 25% average for the drive cycle the bus is on. Diesel engines suffer less from this effect, that was my point.

@Anne, if you look at the average over the industry for quoted (EU cycle) mpgs for gasoline vs diesel powered passenger vehicles, for equivalent performance in the same vehicle the diesel gets on AVERAGE 30% more mpg than the gasoline version. Occasionally it is as much as 40% higher.

This is despite the almost invariable weight penalty that the diesel powered vehicles must suffer with their heavier engines and transmissions, often adding 100-150 kg to the kerb weight of the vehicle.

For example (from a previous discussion of this topic using data from http://www.parkers.co.uk/choosing/specs/):

Comparison of vehicles with equivalent power outputs:

[Make, model] -- [gasoline mpg] -- [diesel mpg] -- [improvement]

Audi A4 ----------- 36 --- 51 --- 42 %
BMW 5-series ------ 31 --- 47 --- 52 %
Ford Fiesta ------- 47 --- 64 --- 36 %
Honda Accord ------ 38 --- 52 --- 37 %
Freelander -------- 27 --- 37 --- 37 %
Merc C-class ------ 38 --- 47 --- 24 %
Peugeot 206 ------- 45 --- 65 --- 44 %
Skoda Fabia ------- 47 --- 61 --- 30 %
Toyota Yaris ------ 50 --- 64 --- 28 %
Vauxhall Vectra --- 38 --- 49 --- 29 %
VW Golf ----------- 40 --- 53 --- 33 %

The AVERAGE improvement of the official economy rating of these vehicles is 36% for the diesel vs the gasoline, even though in some cases it isn't always this much.

Miami, Florida, USA for a while allowed private bus lines (early 2000s), usually 15 passengers vans in private routes (paralleing public transportation routes).. extremely popular with the public, quick, low waiting time and responsive.. they were an eyesore because no two of them had the same paint job or logos. The public bus system got real upset because no one would ride their bigger and more confortable buses (and heavy drain on public funds) and as a result they got the private busses banned, supposedly due to safety issues but that was crap.

So, the conclusion is that public transportation systems can be profitable, only when the government gets involved is that it becomes a mess.

I looked it up in Google, the famous Jitney explosion in Miami, Fl.. people actually stopped driving their cars to ride these busses.. and gas was cheap then!

http://tinyurl.com/6r4hrh

http://www.i2i.org/main/article.php?article_id=835

@Stan

First you cry conspiracy theory to an actual event that GM did get convicted of and then you cry foul and say that public transport is committing a conspiracy itself. In this way only facts you choose to take into account are accounted for. Pure sophistry.

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

Public transportation provides a great service and not all of them are solely publicly owned. In it's history many different parts of many different systems were privately held and today still are. Some bus lines in NY for itstance still are private.

Without public transportation huge amounts of public money would have to be spent on roads and the congestion problems alone that are aleviated are worth the public investment. The Tokyo public transporation system takes almost 3 billion rides a year. You cannot shift that much onto the roads without chaos.

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

The net benefits and costs clearly make public transportation a smart strategy. Only in certain newer growth cities or newer areas of older cities where the infrastructure was put in (and densities are low) when gas was cheap is there problems with public transportation. In recessionary/tough times, these areas of low access to public transportation are usually the first to be abandoned and lose their value the quickest. These low density areas are inherintly inefficient.

TTC buses average 3.5 MPG

"CTA’s oldest buses average 2.77 miles per gallon and its 40-foot hybrid buses average 3.95 miles per gallon...DesignLine Hybrid has averaged seven to eight miles per gallon in other cities and the test period will help determine if the buses will run as effectively in Chicago"

I suppose that these public entities that are open to public scrutiny are all in this conspiracy to elevate their numbers. Which is all the stranger, that some are reporting less than promised numbers in some cases for the newer hybrids (irony). Right...

http://www.hybridcenter.org/hybrid-transit-buses.html

@Brian P

Perhaps you are right about TSI engine being very modern, but I assume the TDI is equally modern.

Your point about a diesel being usually heavier than a gasoline car is correct, however the difference is negligable. A diesel is around 100 kg heavier, which is around 8% for a modern car, and with weight accounting for 25% of fuel consumption (correct me if I am wrong), that only has a fuel consumption penalty of 2%.

Your example for the Jetta indeed shows an increase of 64% for highway use. If we include the ~10% lower energy content of gasoline the value drops to 47% less efficient. My point after all was about efficiency, not mpg's.

Going further, the 2.5 l gasoline has 125 kW, the 1.9 TDI 77 kW. So you are not comparing cars that are more or less equal. The gasoline version has 60% more power!

Finally, in the USA you love displacement. In Europe we use much smaller engines with much lower consumption. So the diesel Jetta is equal to the European version. The gasoline is 'Americanized' with a 2.5 l monster engine (from a European perspective that is :-).

The european version of the Jetta with an ordinary (no TSI) 1.6 l gasoline engine of 75 kW (comparable to the TDI) consumes 9.9 l/100km city, 6 l/100 km highway and 7.4 l/100 km combined, which is a diesel equivalent of 9, 5.4 and 6.6 resp. The data for the TDI are 6.6, 4.5 and 5.2 respectively. This is an increase in consumption of 36%, 20% and 27% (energy equivalent of course).

This was all based on the normal entry level 1.6 l engine which hardly anyone will buy. This 1.6 l base engine is old technology on its way out, still kept for advertising purposes (avaliable from xxxx euro's!). In reality, everyone will go for the TSI, which has much lower fuel consumption and is only 1400 euros more expensive. The 1.4l TSI which has 90 kW, it is rated 5.2 l/100 km highway, which is 4.7 l/100 km diesel equivalent. So hardly any worse than the diesel.

The times they are a-changing.

@Clett:

Thanks for the data, much appreciate the effort. I was however a little surprised to see that you compared mpg's. I thought I was being clear enough that my point is about efficiency, and not mpg's. Therefore you should correct for the lower energy content of gasoline.

Let's look at the worst offender:

BMW 523i - BNW 520d

The 523i has 10 kW more power, the 520d weighs the same (10 kg more which is negligable). The fuel consumptions in l/100 km highway/city combined are: 5.7/10.1/7.3 and 4.3/6.5/5.1

When converting the gasoline numbers to diesel equivalent (10% less energy),they become: 5.1/9.1/6.6. This represents an increase of 19%/40%/30%. So I would say 30%, not 52%.

Even without the 10% correction, the gasoline version on average only consumes 42% more than the diesel. Perhaps you compared a more powerful gasoline car to the diesel? Or, like I already noted in my reaction to Brian, the gasoline version is an 'Americanized' model with larger displacement?

Let's look at another 'offender', the Peugeot 206 which you attribute a 44% higher consumption for the gasoline model.

I have to compare the newer 207, which I believe has the same engines as the old model. I compare the 1.4 16v VTI 70 kW gasoline engine to the 1.6HDI 66 kW. Again the performance is comparable. The weight of the HDI is 60 kg higher (5%), which should yield a 1% higher consumption.

The fuel consumption of the diesel is: 3.8/5.8/4.5, and the gasoline: 5.0/8.1/6.1, which is in diesel equivalent: 4.5/7.3/5.5, an increase of 18%/25%/22%. Add another percent to correct for the higher weight of the diesel version if you want.

If I look at your other examples and correct for the difference in energy content, then much of the diesel advantage melts away. Diesel is more efficient indeed, but the difference is not a big as it seems. Or are you comparing the 'Americanized' gasoline version to a European diesel.

I think you also overstate the weight penalty of a diesel, which is usually well below 100kg, not 100-150 kg. This represents only 5% of the weight and if weight accounts for roughly 25% of consumption, a consumption penalty of little over 1%.

My point stands: diesel is NOT 60% more efficient than gasoline. At best 25% percent. And (as I showed with the Jetta TSI example), the gap is narrowing.

Finally, I can not say this often enough: this is NOT about mpg, but about thermal efficiency.

Thanks, Anne, for the valuable direct-comparison data.

Indeed, diesel is only 18-20% more efficient than gasoline in highway mode, and may be even less when the engine is downsized and used at higher manifold pressure wherein there is less pumping loss, like in HEV application. As such, gasoline engine offers better exhaust emission at lower cost when used in HEV application.

This article is a good illustration of "How Not to Do Electric Hybrid", like I've mentioned earlier.

@Anne,

Fair enough, I was probably being pessimistic regarding the thermal efficiency of the Ford V10 bus engine by guessing 25% (but who wouldn't be!)

If it was a comparison between 25% thermal efficiency and 40% efficiency, then you're right that would suggest 60% further per gallon (assuming, as I still maintain, that the volumetric energy density of diesel is largely countered by the increased weight of the diesel drivetrain).

However, if the thermal efficiency of the gasoline engine was 30% and the diesel 40%, that means the diesel vehicle should go 33% (rather than 60%) further from the same chemical energy stored in the fuel.

Perhaps this is closer to the truth as that differential holds up pretty well with the published figures for many cars on the market today (at least with modern, more efficient gasoline engines, I still don't think that Ford V10 will be in the same thermal efficiency bracket as a downsized TSi!).

Why are they driving those huge buses when
they should be running shuttle-vans like the
airlines do? You'd see a dramatic drop in fuel
consumption then. Most of the buses in our
area have very little ridership. The only ones
I see riding them are 1 half-way house person
& the local bag lady. A van will do. Make it
a HEV or a PHEV. If it fills up, a quick call
on the radio should get another van there quickly.
I don't know how many seats are on that monstrosity
we pay for, but most of the seats are empty. At
least, our runs on CNG.

Btw, gasoline also produces less CO2 per energy than diesel.

Here's another car comparison:

Citroën C1 1.0 (gasoline engine):
Power: 50 kW
Average fuel consumption: 4.6 l/100 km
CO2-emission: 108 g/km

Citroën C1 HDI 55 (diesel engine):
Power: 40 kW (20% less)
Average fuel consumption: 4.1 l/100 km
CO2-emission: 109 g/km

Well, it looks like everyone here overlooked the most important factor in determining if this particular gasoline-electric hybrid bus is a viable alternative to the diesel bus: the bottom line.

Total cost per mile $1.05 Gasoline Hybrid
Total cost per mile $1.19 Diesel

(Sure, ideally you would run all buses on 100% renewable energy, but you can't run a city transit system on ideals. You have to run it on limited funds and field proven vehicles.)

Fred H:

In your total cost per mile, could you add, capital purchase or devaluation cost, interest cost, parts and maintenance cost, operation cost ($60+/hour/driver or about $6+/mile in most cases) +fuel cost?

One of the most important cost is often the driver's cost, specially on a per mile basis. That may be the main reason why city buses are very large, with a total capacity of up to 160 passenger.

Ideally, 160-passenger units should be used during peak hours and 15-passenger units (with lower half cost drivers) for off peak hours. Airlines do it, with half cost pilots and smaller planes, to survice on low density routes.

Hi HarveyD,
Sorry I can't add depreciation or interest cost. You might ask Long Beach Transit.
Parts and maintenance cost and fuel cost are included. See tables 7,8,9, and 11.
I would assume driver cost is the same for both.

Natural gas hybrid would be a good way to go. California imports a lot of natural gas for power plants, but converting every city bus to NG would have little effect on consumption of NG as a percentage used.