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Re: Also remember that diesels are now a lot cleaner
Author: mook
Date: 01-25-2014 - 17:47
Then there are the counter-arguments that I keep hearing from the NG people:
NG is much cheaper on a diesel-equivalent-gallon (energy content) basis than diesel, and probably will be for a long time. For most transit systems, especially if they can get somebody else (CMAQ? Air District?) to pay for the fuel stations and the extra cost for the buses, this overrides all other considerations.
Naturally lower particulate (as you state, SP O.) but it's a different type - jury is out as to whether it's better than well-filtered diesel (could be toxic in a different way). Particulate filters work on NG buses too.
The NOx thing isn't as bad as it seems with modern engines, and SCR catalyst works as well on NG as it does on diesel.
The GHG issue is arguable, and the studies aren't compelling either way, but I suspect you're right. Diesel engines are more thermally-efficient - more power per equivalent energy input - so NG is at a disadvantage to start with. Then there's the fact that NG itself is mostly methane, so the inevitable leaks are of a more-potent GHG than the CO2 from exhaust.
NG does have a problem on the bus that is significant for some services: storage. CNG is relatively easy to set up and use, but doesn't store any where near as much energy as diesel. CNG buses in urban service often can stay on the road for only 1/2 shift if distances covered are significant - drivers bring them in for fueling or exchange for another one at lunch break, resulting in more deadhead time and need for a bigger fleet. LNG can go much farther per tank (equivalent to most diesel) but the cryogenic stuff can be a problem. Then there's the tank recertification stuff for pressure (CNG) or cryo/pressure (LNG) - tanks are unlikely to last the 12 years the bus has to if Federal $$ are involved.
On balance, if a transit system that can operate out of one or two fleet depots with high-volume fueling at those sites, and doesn't have very long runs, and it's willing to make the investment (especially if somebody else's money is available), CNG makes a lot of sense. Systems that have longer/steeper routes, and can't conveniently operate out of one or two yards, may find it better to stick with diesel (Tier 4 diesel isn't any dirtier, really, than current CNG) and add hybrid for runs with a lot of traffic congestion. Diff'rent strokes...
What does all this have to do with trains? Not a lot. But it's a piece of thought process that perhaps explains why line-haul CNG or LNG locomotives are an experiment at best. Local switching, or a shortline that runs out of one shop, might be more interested. Tier-4 diesel, with an eye toward eventual switch to biodiesel, will probahly take over fairly rapidly in the next 5-10 years in traditional roles (with a little help, of course, from Other People's Money in some areas).
Electric will remain a non-starter for anything other than commute lines - costs too much to build for general use. There are good reasons why the early-1900's electric main lines are all gone except the NEC (which is mostly a Really Big Commute Line).
NG is much cheaper on a diesel-equivalent-gallon (energy content) basis than diesel, and probably will be for a long time. For most transit systems, especially if they can get somebody else (CMAQ? Air District?) to pay for the fuel stations and the extra cost for the buses, this overrides all other considerations.
Naturally lower particulate (as you state, SP O.) but it's a different type - jury is out as to whether it's better than well-filtered diesel (could be toxic in a different way). Particulate filters work on NG buses too.
The NOx thing isn't as bad as it seems with modern engines, and SCR catalyst works as well on NG as it does on diesel.
The GHG issue is arguable, and the studies aren't compelling either way, but I suspect you're right. Diesel engines are more thermally-efficient - more power per equivalent energy input - so NG is at a disadvantage to start with. Then there's the fact that NG itself is mostly methane, so the inevitable leaks are of a more-potent GHG than the CO2 from exhaust.
NG does have a problem on the bus that is significant for some services: storage. CNG is relatively easy to set up and use, but doesn't store any where near as much energy as diesel. CNG buses in urban service often can stay on the road for only 1/2 shift if distances covered are significant - drivers bring them in for fueling or exchange for another one at lunch break, resulting in more deadhead time and need for a bigger fleet. LNG can go much farther per tank (equivalent to most diesel) but the cryogenic stuff can be a problem. Then there's the tank recertification stuff for pressure (CNG) or cryo/pressure (LNG) - tanks are unlikely to last the 12 years the bus has to if Federal $$ are involved.
On balance, if a transit system that can operate out of one or two fleet depots with high-volume fueling at those sites, and doesn't have very long runs, and it's willing to make the investment (especially if somebody else's money is available), CNG makes a lot of sense. Systems that have longer/steeper routes, and can't conveniently operate out of one or two yards, may find it better to stick with diesel (Tier 4 diesel isn't any dirtier, really, than current CNG) and add hybrid for runs with a lot of traffic congestion. Diff'rent strokes...
What does all this have to do with trains? Not a lot. But it's a piece of thought process that perhaps explains why line-haul CNG or LNG locomotives are an experiment at best. Local switching, or a shortline that runs out of one shop, might be more interested. Tier-4 diesel, with an eye toward eventual switch to biodiesel, will probahly take over fairly rapidly in the next 5-10 years in traditional roles (with a little help, of course, from Other People's Money in some areas).
Electric will remain a non-starter for anything other than commute lines - costs too much to build for general use. There are good reasons why the early-1900's electric main lines are all gone except the NEC (which is mostly a Really Big Commute Line).
