It sounds like you might want a series hybrid CNG diesel bus that loads the engine properly for maximum mileage and gets the economy of a hybrid. These are good studies that show the magnitudes of performance with various configurations.

With all the high grade waste heat, they could use abosorption cooling and use not extra power at all. It is a bus, with a lot more room than a truck or car for the cooling unit.

wow, so the thing that i've been saying all along, this whole time, has finally been proven by months of testing – a CNG bus is simply not a "clean air" vehicle. i still cannot understand for the life of me why people want to insist on buying CNG buses instead of going for the diesel-hybrid route.

CNG is considered "clean air" because it releases far less PM and other local pollutants, relative to conventional diesel buses, even given its lower fuel economy. Cleaner diesel technology has narrowed the gap, but CNG still has the edge there.

Hybrid diesels that combine low emissions and high economy are nearly as clean as CNG in terms of local pollutants per mile driven, but cost a whole lot more to buy on the front end. They can make that up in fuel and repair cost savings (hybrid buses wear out their brake pads much more slowly than conventional buses), but only if they are substituted into appropriate routes -- stop and go city center routes, not high speed, hilly or more suburban ones.

Still, considering previous studies which examined the fuel economy performance of hybrid buses, this study is encouraging. Previous studies would often put hybrids into service on routes which did not take full advantage of their capabilities; this study seems to openly acknowledge the importance of route selection, and confirms the hybrid advantage on well chosen routes.

SJC -

an absorption chiller would be a great way to deliver airco in city buses. Since diesels are turbocharged, it could also be used to drive a chiller between the intercooler and the intake manifold to further cut the temperature of the fresh charge. With an air/water intercooler, the waste heat from the first stage can actually help drive the second. Charge chilling should boost rated power and/or reduce engine-out NOx levels.

The fly in the ointment is that traditional absorption chiller designs (other than small hotel/RV refrigerators) rely on the gravity-induced flow of a finely dispersed mist to achieve adequate re-absorption by the weak ammonia solution. Experiments on ships have shown that the chiller power of such designs is highly susceptible to vibration, making them unsuitable for mobile applications. The porous membrane absorber stacks under development in Germany are much more compact and impervious to vibrations.

http://www.itt.uni-stuttgart.de/~schaal/index.en.html

Keep in mind, though, that absorption chillers are quite expensive. Once mechanically robust solutions are available, they should initially be considered for buses and refrigeration trucks with life expectancies of 1-1.5 million kilometers to permit amortization of the up-front premium.

Actually, numerous studies have shown that CNG is typically much worse in NMHC emissions, including the associated air toxics. Even when equipped with catalysts, CNG NMHC emissions are somewhat higher than clean diesel NMHC emissions (which are usually near or below detection limits) according to a study by CARB.

NMHC is the worse possible pollutant for urban air quality.

SJC,
The Orion VII hybrid is a low floor bus. It may fit on the roof, but that could change the center of gravity. One may be able to fit a unit on the rear of the vehicle, or mounteed on a trailer fluid&electric w/couplings. The Orion Bus site has the Thermo King AC at 100,000+ BTU unit.
___The batteries could use updating. I went over the Resources link and the PDF states that they are lead acid units. Li-ion could be make large improvments to fuel mileage in stop and go driving. It would also:
a) drop the mass of electrical energy storage.
b) increase energy storage capacity.
c) lend to plug-in bus experimentation and implementation.
On the flipside, Li-ion units are expensive vs lead acid.
_
Rafael,
That is why they are found mostly on buildings. Many office towers/large buildings away from the waterfront in Manhattan use absorption chillers (+ heating during winter) powered via ~350 F steam from co-generation electric+steam plants.

NMHC is the worst possible pollutant for urban air quality
What's NMHC?

NMHC refers to "non-methane hydrocarbons," and Carl's phrasing should therefore read "NHMCs *are* the worst possible..."

But as to the substance of that statement, NMHCs are a range of compounds, and the statement that they are "the worst possible" form of local air pollution is a vague one at best. By what standard? Which NHMCs are particularly nasty, and under what circumstances? I am better acquainted with the dangers associated with PM and NOx emissions, so I would appreciate a link to the CARB study mentioned earlier in order to get more background information on these questions.

Methane is a GHG. If we have fuel cells with reformers to turn SNG into H2, we would have no tailpipe emissions other than CO2 (neutral) and H2O.

It seems to be an ideal vehicle for 140+ KWh Altairnano new quick charge-discharge batteries.

In city traffic situation, these batteries would allow much more breaking energy recuperation to operate the cabin heating/cooling system.

Some 40+ square meters of high efficiency (25% to 30% = about 1.1 x .25 x 40 x 6 = 66 KWh/day) solar panels mounted on the large bus roof would also help to keep the batteries charged when most needed = during the 6 to 8 hrs/day of bright sunshine.

An up-to-date very light weight, compact, very high efficiency 23-SEER, 8 to 10 Ton heat pump, (preferably 2 units x 4 to 5 Ton) equipped with variable ECM motors would to the HVAC job year round in most cities. Why re-event the wheel when it is there already.

This type of city bus could be built now and would need a much smaller diesel genset.
Dozens of USA/Canadian firms could do it with adequate R & D support.

I was not responding to anyone, just pointing out that methane is a GHG. Keep methane out of the air, simple as that.

Carl-

The two presentations you posted are certainly eye-opening when it comes to comparing CNG to clean-diesel in the 2002 time frame. I wonder if newer CNG buses have oxydation catalysts (these presentations seem to imply that the older ones did not), and if so, whether that puts them decisively over 2002-era clean diesels as far as local air quality issues go. All the same, the newest diesel technologies can make the real target a moving one.

The cost issues identified in the second presentation in particular confirmed what I had long suspected, which is that a conversion to a CNG fleet is quite expensive. Taking into account infrastructure costs, my gut always leaned towards the diesel-hybrid approach, as against a conventional CNG drivetrain. Though a good series-hybrid layout might be able to take maximum advantage of CNG, and be worth the cost.

Thanks for posting a response.