Much has been made in recent years of the possibility that fuel-cell-powered electric vehicles (FCEVs) might provide substantial reductions in automotive energy consumption and emissions.  However, while some automakers concentrate on developing FCEVs, others are taking a different tack – they are developing vehicles that burn hydrogen instead of gasoline in internal combustion engines (ICEs). By Joerg Dittmer, Industry Analyst for Frost & Sullivan’s Transportation Group.

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The Pros and Cons of Hydrogen as a Combustion Fuel


Advantages of hydrogen as a fuel in internal combustion engines are:



  • Hydrogen is a renewable fuel that can be derived from water through electrolysis, and it can be extracted from petroleum or natural gas.
  • Since there is no carbon in hydrogen fuel, there are virtually no tailpipe emissions of carbon monoxide or carbon dioxide (CO2).  Thus, hydrogen may help automakers meet the CO2 regulation that California is considering.
  • Automakers have substantial experience with internal combustion engines, while fuel cells are a relatively new technology.
  • Energy efficiency of a hydrogen ICE is 20 to 25 percent better than that of a gasoline ICE because a hydrogen ICE resembles a diesel engine in some of its operating characteristics.

Specifically:



  • Hydrogen can be used at very lean air:fuel ratios,
  • Hydrogen can be used in higher-compression engines, and
  • A hydrogen-fueled engine can be controlled without a throttle.

Unfortunately, hydrogen also has a number of disadvantages in this use:



  • If hydrogen is combusted near its stoichiometric air:fuel ratio, high combustion temperatures result in the formation of oxides of nitrogen (NOx), which have to be cleaned up by a catalytic converter.  (However, the catalytic converter does not have to deal with hydrocarbons or carbon monoxide.)
  • Formation of NOx can be mitigated by running the engine on a lean air:fuel ratio, which reduces combustion temperature.  However, this strategy also reduces power and performance.
  • CO2 is released if hydrogen is extracted from petroleum or natural gas, offsetting the clean combustion of hydrogen in the engine.  (The amount of CO2 released is about 80 percent of that released in refining and combusting gasoline.  When generated centrally, sequestration of CO2 is more feasible than when generated by burning gasoline in individual vehicles.)
  • By volume, a vehicle uses 3.5 times more liquid hydrogen than gasoline, so fuel storage takes substantial space onboard a vehicle.  (This problem can be mitigated by designing a vehicle specifically for hydrogen storage.  Today’s test vehicles are converted gasoline-powered cars.)
  • Whether as a compressed gas or a super-cooled liquid, hydrogen is more difficult to handle than gasoline.  Since liquid hydrogen has to be kept at 423°F below zero, the refueling stations that have been set up are fully automated.  Refueling with compressed hydrogen is similar to refueling with compressed natural gas.
  • The cost of hydrogen may be higher on a per-mile basis than today’s cost of gasoline, even when hydrogen is produced in large volume for use as a fuel.  In particular, liquefaction (turning gaseous hydrogen into a super-cooled liquid) is expensive.
  • A hydrogen refueling infrastructure would have to be developed.
  • Liquid hydrogen tanks have to be well-insulated and gaseous hydrogen tanks have to withstand high pressure, so they add to a vehicle’s cost.
  • Up to two percent of the fuel in a liquid hydrogen tank can be lost to evaporation per day.

Implications for Fuel Cell Electric Vehicles


Interestingly, some of BMW’s hydrogen-fueled ICE test vehicles carry fuel cells, supplied by UTC Fuel Cells, to generate electricity for accessories.  This improves fuel economy by reducing the load on the internal combustion engine.  Thus, hydrogen-fueled ICE vehicles may benefit FCEVs in several ways:



  • Experience in handling hydrogen will be gained.
  • If hydrogen-fueled internal combustion engines catch on, fuel cell vehicles may have an easier time finding acceptance, once they become available, because a hydrogen refueling infrastructure will already be in development.
  • Introduction of fuel cells for auxiliary power may help that technology to develop and to gain public acceptance.

To date, one of the questions concerning FCEVs has been, should they be fueled with hydrogen, or should they be fueled with gasoline from which an onboard reformer extracts hydrogen?  Onboard reformers avoid the chicken-egg problem that FCEVs are not feasible until a refueling infrastructure exists, while a refueling infrastructure is not viable until many FCEVs are on the road.   Hydrogen-fueled ICE vehicles may offer a second route to hydrogen-fueled FCEVs, as illustrated in Chart 1.










Chart 1 Hydrogen as an Automotive Fuel:
Two Routes to Hydrogen-Fueled Fuel Cell Electric Vehicles

Source: Frost & Sullivan

Who’s Doing What?


BMW and Ford Motor Company are two leading developers of hydrogen-fueled ICE vehicles.  BMW regards ICE-powered vehicles as more suited to its performance orientation than FCEVs, and doubts that fuel cells will be robust enough for automotive application any time soon.  Ford regards FCEVs as the ultimate goal, with hydrogen-fueled ICE vehicles as possibly easing a transition to FCEVs.  Ford is developing hydrogen ICE and FCEV technologies simultaneously.


BMW has worked on hydrogen ICE technology for more than 20 years, and is testing about 20 prototype vehicles.  The most recent model, based on the 7?series sedan, is called the 750hL.  This vehicle can run about 220 miles on hydrogen and another 370 miles on gasoline.  The dual-fuel capability is needed until hydrogen refueling stations become common.  Hydrogen is stored as a super-cold liquid onboard the 750hL.


Ford Motor Company has been testing a prototype hydrogen ICE vehicle for about 18 months.  Called P2000, this vehicle is based on stretched Ford Contour.  Range depends on the pressure at which hydrogen is stored – 160 miles with 5,000 pounds per square inch (PSI) tanks, 270 miles with 10,000 PSI tanks.


To attain low-emissions-vehicle (LEV) status in terms of NOx without a catalytic converter, the P2000 cruises at a very lean air:fuel ratio of 86:1, compared to hydrogen’s stoichiometric ratio of 34.2:1.  In terms of carbon-based emissions, the P2000 meets the super-ultra-low-emissions-vehicle (SULEV) standard, since the only carbon-based emissions result from lubricating oil. 


Ford claims an 18 percent improvement in fuel economy for the P2000 relative to a similar gasoline-fueled vehicle, in terms of the energy content of the fuel used.  In the next generation of test vehicles, Ford plans to use boosting to offset the power penalty of lean combustion, and to add aftertreatment for NOx to attain SULEV status.  The relative improvement in fuel economy is expected to rise to 25 percent.


When Will It Happen?


If demand existed, hydrogen-fueled ICE vehicles could be put into large-scale production within a few years, because these vehicles represent a relatively small leap in technology.  However, demand presupposes:



  • Cost-competitiveness of hydrogen-fueled vehicles, compared to today’s vehicles,
  • Cost-competitiveness of hydrogen, compared to gasoline, and
  • The existence of a refueling infrastructure.

These conditions could come about as a result of a drastic change in the world’s supply of petroleum, or through government action.  Government action might be taken in anticipation of a change in the supply of petroleum.


Estimates of the current cost of one kilogram of hydrogen (regarded as the equivalent of a gallon of gasoline) range from $1.25 to $4.66.  (This price should be compared to the cost of gasoline net of all taxes.)  Even a 25 percent improvement in fuel economy may not offset the cost penalty of this price.  Government incentives may help put a limited number of hydrogen-fueled vehicles on the road.  However, for a mass market to develop, either a substantial reduction in the cost of hydrogen or a substantial increase in the cost of gasoline would be needed.


Hydrogen-fueled ICE vehicles are technically feasible, but the economic aspect of supplying hydrogen remains a major hurdle.


Further reading:


BMW’s hydrogen-based vision of ‘sustainable mobility’


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Frost & Sullivan
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