Hydrogen vs LNG

It is my understanding that for the foreseeable future, the most practical source of hydrogen for fuel-cell powered automobiles is to utilize an on-board steam reformer to convert methane or propane. It seems to me to be very inefficient because all the fuel value of the carbon goes off as waste heat as it is converted to CO2 which is vented as greenhouse gas just like in combustion. Then you have to consider the losses as the hydrogen is tranformed into electricity in the cell and then to mechanical power through the motor.

Here’s the question:

With the same tank of LNG, would I go further in my automobile with a gas-powered combustion engine or with a reformer/fuel cell/electric engine?

I’m not sure if this will totally answer your question, but here’s a start: Argonne Nat’l Labs did a fairly extensive study (big pdf!) that looked at the well-to-wheel efficiency of a number of different technologies. Well-to-wheel is a term used to indicate that all sources of inefficiencies are included, both in the vehicle (tank-to-wheel) and in processing the fuel beforehand (well-to-tank). They looked at, among other things, a conventional spark IC engine powered by compressed natural gas (rather that liquid), a hydrogen fuel cell vehicle (where the hydrogen was formulated from natural gas), a hybrid version of the same fuel cell vehicle. Here’s the data, in BTU/mile (the lower the number, more efficient it is):

                     Estimated Energy Use
Type     Data Source  Median   High  Low
CNG SI    Fig 3.4      7200    7700  5500
CNG Hyb   Tab 3.8      6000    6500  4600*
Fuel Cell Fig 3.10     5100    4500  5700
FC Hyb.   Fig 3.7      4600    4000  5000
*My estimation from other hybridized IC engines

This indicates that the fuel cell vehicle is indeed more efficient than a straight CNG IC engine. However, a couple grains of salt: first, I believe that the calculations are made here using projected efficiencies for fuel cells, not efficiencies currntly available. Second, the calculations are made assuming that the conversion from natural gas to hydrogen is done at a central station, not on board the vehicle. I’d have to assume that onboard conversion would be less efficient and would likely add more weight to the vehicle, both of which would drive the energy use up.

That’s the best answer I’ve seen yet so I thank you for that source. I’m going to download the whole report to see if I can get the piece parts I need to construct my own analysis. However, as you point out, the figures provided do not represent what is available in the near term. It is not practical in the foreseeable future to expect consumers to use compressed hydrogen because the pressures are unreasonable to get enough mass on board. It is not reasonable to expect a liquid hydrogen infrastructure either. So the only current solution is on-board reforming which will probably net out to be about the same efficiency as spark combustion of CNG. The complexity and capital cost of the reformer/fuel cell combo will like be far higher than the highly optimized IC engine.

My paranoid side suspects that the current white house’s promotion of hydrogen is because they know that it will maintain current consumption levels of hydrocarbon with no advantage in greenhouse emissions either.

I think we need a breakthrough in hydrogen storage technology for this to become practical. Then gas stations can be central reformers dispensing hydrogen to your vehicle.