Hydrogen is often mentioned as being the best option for a clean-burning future fuel. Hydrogen is depicted as being used either in combustion or in the production of electricity via a fuel cell that mixes hydrogen and oxygen. While it is true that the waste products of hydrogen-powered vehicles would be almost completely devoid of pollutants, the use of hydrogen as a fuel source is not currently economically or environmentally viable. This is because it takes significantly more energy to actually produce the fuel itself than that which is released when it is used in an engine. Hydrogen fuel does not occur naturally on Earth and thus is not an energy source, but is an energy carrier.
In a 2002 article in Automotive Fleet, the research company Frost & Sullivan outlined the "pros and cons" of hydrogen fuel.
Much has been made in recent years of the possibility that fuel-cell-powered electric vehicles (FCEV) might provide substantial reductions in automotive energy consumption and emissions. However, while some automakers concentrate on developing FCEVs, others are developing vehicles that burn hydrogen instead of gasoline in internal combustion engines (ICE). According to research done by Frost & Sullivan, 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.
- Research by the company indicates that 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.
- A hydrogen-fueled engine can be controlled without a throttle. Unfortunately, hydrogen also has a number of disadvantages in this use. According to the com-pany, 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. 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. 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. 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. 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.
- According to the company, hydrogen-fueled ICE vehicles are technically feasible, but the economic aspect of supplying hydrogen remains a major hurdle.