The Internal Combustion Automobile Engine

Over the last 25 years, interest in hydrogen has resulted in a number of projects for the conversion of standard automobiles to hydrogen fuel. The early projects in the United States 200 were performed by the following organizations:

University of Southern California, University of Miami (Florida), University of Denver Research Institute, Los Alamos Scientific Laboratory, and Billings Energy Company (Utah).

Today Hydrogen Components Incorporated, in Denver Colorado will convert any ground-based vehicle and some water-based vehicles to the use of hydrogen fuel. The Japanese national government has sponsored a number of automobile hydrogen conversions in conjunction with their Project Sunshine research of alternate energy sources. Universities and university-industry teams have performed these efforts.

The West German Companies, Daimler Benz and BMW have also performed studies and converted autos. All these projects have had two major elements: 1- conversion of the internal combustion

200 Escher, W. J. D., "Hydrogen-Fueled Internal Combustion Engine, A Technical Survey of Contemporary U. S. Projects", United States Energy Research & Development Administration, TEC-75/005, ETA Report PR-51 September 1975

engine for operation with hydrogen fuel, and 2- demonstrations of techniques for the storage of hydrogen on board the vehicle.

The majority of existing vehicles powered by internal combustion engines utilize a liquid fuel, either gasoline or diesel. There are, however, a small percent fueled with gaseous butane, propane or natural gas. The engineering principles used in the butane, propane and natural gas vehicles are applicable to hydrogen use. 201 The actual hardware used is not directly transferable to hydrogen systems without modification because of the large difference in the air to fuel mixture ratios. These ratios are shown in Table 7.1.

Mixture

RATIO A/F BY VOLUME

RATIO A/F BY WEIGHT

FUEL

STATE

Gasoline

(Liquid)

8500

16

Propane

(Gas)

27

18

Natural Gas

(Gas)

11

20

Hydrogen

(Gas)

2.7

40

Table 7.1 Air to Fuel (A/F) Mixture Ratios

(All ratios are based on air and fuels at zero degrees centigrade)

Only a small volume of air is required per volume of hydrogen when compared to the air required with propane and natural gas. If used as is, the propane and natural gas equipment would mix too little hydrogen with the air. The mixture ratio differences are so large simple mechanical modification of the equipment is inadequate to achieve the proper hydrogen to air mixtures. For some of the listed demonstration programs the principles embodied in propane and natural gas mixing devices were utilized to construct special purpose hydrogen mixers. In other conversion projects, injection of gaseous hydrogen was used to obtain the proper air-fuel mixture.

In the first experiments, engines were equipped with improvised air-fuel mixing devices and tested. These devices were superficially similar to the propane and natural gas mixing devices. The engines ran from the first tests; but there were problems. Hydrogen has different ignition and burning characteristics compared to other fuels. It seems quite sensitive to ignition from hot spots in the motor, internal deposits and residual hot exhaust gas. The air-hydrogen mixture also exhibits a very high flame speed. As a result, all the early conversions showed a great tendency for a flame to propagate from the cylinders through the intake manifold to the mixing device. At best, this flashback caused severe miss, noise and unstable operation. In some cases, the fire was sustained and the mixing device was destroyed.

Several techniques to overcome this problem were evaluated. These included: exhaust gas recirculation, water injection, extremely lean fuel ratios, adjustments in valve timing and maintaining the intake path free of catalytic effects. None of these approaches resulted in an engine with the desired performance. Exhaust gas re-circulation, water injection, and extreme lean fuel concentrations all operate by diluting the flame with an excess gas (exhaust, water vapor or air) to reduce the flame speed. When the mixture was sufficiently dilute to prevent flashback, only a small amount of fuel was burned and engine power output was low.

201 Gray Jr., Charles L., von Hippel, Frank, "The Fuel Economy of Light Vehicles", Scientific American, Vol. 244, No. 5, May 1981, Page 48

Several automobiles were converted to hydrogen fuel using one or more of these principles. Changes in the valve timing were only slightly helpful in reducing the frequency of the flashback. Establishing an extremely clean and passive intake path resulted in significant improvements. However, it was difficult to maintain and did not thoroughly suppress the pre ignition problem.

These conversions operated safely without flashback; but all the performance factors depending on engine power were poor. Eventually, two solutions to the flashback problem were found. Either dual path mixing channels or injection at the intake valve allowed the design of hydrogen-fueled engines suitable for routine use.

Workers at the Denver Research Institute reasoned flashback was the result of the very high flame speed of the stoichiometric (chemically balanced) mixture of air and hydrogen. If they could find a method to effectively reduce this high flame speed without the use of power robbing dilution, the problem would be solved. They equipped a stratified charge engine using two intake valves with two separate air-hydrogen mixing devices. Through one intake valve, they introduced an air-hydrogen mixture that was so hydrogen rich it had a low flame speed. Through the other valve they introduced a mixture so hydrogen lean it also had a low flame speed. This technique provided a dual path for the mixing of the hydrogen and the air. The two streams where adjusted to provide a final in-cylinder mix that was near the desired stoichiometric mixture. This technique was successful. The converted engine could be run with an optimum mixture ratio without any tendency to flashback through the air-fuel mixing device.

The workers at the University of Miami took a different approach. They reasoned if the fuel could be introduced into the air stream at a position where no flashback was possible, the problem would be eliminated. They equipped a standard engine with gas injectors just inside the intake valve. Hydrogen was injected through the injectors just as the intake valve was closing. With this technique the intake manifold never contains a mixture of air and hydrogen and there is no possibility of flashback.

These two techniques have been demonstrated as available solutions to the conversion of spark ignited internal combustion engines for operation by hydrogen. Either is suitable for the design of a new engine. The two intake valve, two stream technique can be applied to any existing engine with the dual intake valves. The injector technique can be applied to any engine where physical clearances near the intake valve will allow the installation of the injector. With these two schemes, it will be possible to design all new engines for hydrogen operation and convert many existing engines to its use.

Despite the flashback tendencies, hydrogen shows a high effective "octane rating". It can be used in engines with relatively high compression ratios. This, combined with the other combustion characteristics of hydrogen, allows the engine to convert a higher percentage of the potential energy of hydrogen to useful power than is achieved with gasoline. As a result, the hydrogen-fueled vehicle will demonstrate a greater distance per unit of energy (kilometers per liter - energy equivalent) than current technology vehicles.

The other major technology area necessary for the conversion of transportation vehicles to the use of hydrogen is the on board fuel storage. A number of differing storage techniques have been investigated. To aid in the comparison of the various storage schemes it is necessary to establish a set of criteria for a reference vehicle and its fuel tank.

The criteria for the example vehicle are: Vehicle weight of 1200 kg

Fuel capacity equivalent to the energy in 60 liters of gasoline

(This is equivalent to 42.3 kilograms of gasoline). A full tank would provide sufficient fuel to drive 500 kilometers

The criteria for the hydrogen fuel tank are:

1. Reasonable volume and weight,

2. A refuel time of not more than 10 minutes, and

3. Adequate safety.

a. Low fire hazard, b. Low tank internal pressure (low hazard burst) and c. Passenger protection from a cryogenic fluid.

These criteria establish a base line amount of fuel required to operate an automobile of specific performance, weight and range. Because common commercial gasoline is of variable composition, it has energy of combustion ranging from 11 to 14 kilowatt hours per kilogram. The switch from joules per gram to kilowatt-hours per kilogram is made to keep the numbers used easy to compare. One kilowatt-hour is equivalent to 3,600,000 joules. For this evaluation, gasoline is assumed pure isooctane, with combustion energy of 12.8-kilowatt hours per kilogram. The fuel capacity of the reference automobile (43.2 kg.) is equivalent to 551-kilowatt hours of energy. Hydrogen has a heat of combustion of 33.6-kilowatt hours per kilogram. The reference vehicle will require a tank holding 16.4 kilograms (551/33.6 = 16.4 kilograms) of hydrogen to provide an amount of energy, and thus range, equal to that provided by the gasoline. 202 A number of different schemes have been examined for the storage of hydrogen on board an automobile sized vehicle. These are:

1. Reversible absorption to form metallic hydrides,

2. Reversible formation of chemical compounds,

3. High pressure storage in glass microspheres, and

4. High pressure storage in strong cylinders

5. Storage as cryogenic liquid (extremely cold liquefied gas),

Because of the inherent bulk of hydrogen, all methods present a design and engineering challenge in finding the space to store adequate fuel on the vehicle. When storing hydrogen in metal hydrides, or in other chemical combinations, there are the additional challenges of weight, complexity, and long refueling times. The best hydrides only hold about 2% hydrogen. This leads to the need for a tank containing 820 kilograms of metal hydride. The Tank itself will probably weigh another 100 kilograms for a total fuel system weight of 920 kilograms. Today's cars only weigh 1000 to 2000 kilograms. Glass microspheres storage presents these same challenges. They also only hold a few percent of hydrogen. In addition, adequate service life will be difficult to achieve; the glass microspheres are broken by vibration.

202 Ecklund, E. E., "Survey of Liquid Hydrogen Container Techniques for Highway Vehicle Fuel System Applications", U. S. Department of Energy, report HCP/M2752-01, April 1979

Storage as a high-pressure gas is the simplest and requires little development, but is the most bulky. Cryogenic storage will require development but has the potential for the least volume and weight. It will allow rapid refueling. With the established performance criteria, hydrogen stored as a cryogenic liquid is probably the only feasible scheme compatible with the reference vehicle using an internal combustion engine. As you will see later, it is the system adopted by the most advanced hydrogen fueled internal combustion automobile demonstrated to date. All the other schemes result in extremely heavy, bulky, costly or complex storage systems that will not be satisfactory for use in a private automobile.203

A cryogenic storage vessel consists of an inner and outer tank assembled in the same manner as a Thermos® bottle. The inner tank holds the cold (20 Kelvin) liquid hydrogen. The inner tank is centered in the outer tank by supports designed to minimize the heat that can pass from the outside to the inner tank. Supports made from long fiberglass tapes have good performance, but are difficult to install. Pads made from porous plastic reinforced with organic fibers make for easier assembly but leak more heat. Magnetic support provided by permanent magnets pushing against a layer of superconductor coated on the inner tank, will offer high performance if it can be developed.

The space between the two tanks is filled with layers of thin aluminized plastic film separated by a lightweight coarse plastic screen. These serve as a shield against the passage of thermal radiation from the outer to the inner tank. The air between the tanks and around the insulation is removed with a vacuum pump. The high vacuum serves to stop heat flow by conduction. The liquid fill and gas withdrawal lines are coaxial; that is, one inside the other. They are made from materials with low thermal conductivity and are coiled inside the insulation to minimize heat flow down the length of the pipe from the outside into the inner tank.

The inner tank is designed of appropriate materials to be safe at a temperature of 20 Kelvin and with an internal pressure of between 10 and 20 atmospheres. To fabricate quality fuel tanks the proper materials must be selected. Some metals and plastics become very brittle at cryogenic temperatures. Fortunately, several low cost, common metals are suitable for fabrication of the inner tank. These are aluminum, 300 series stainless steel, and some grades of low carbon mild steel. Broad fabrication experience exists for these metals leading to easy implementation of the inner tank technology. A schematic diagram of a cryogenic tank suitable for liquid hydrogen is shown in Figure 7.1.

The hydrogen withdrawal line is equipped with a vaporizer valve that will allow the liquid hydrogen to flash to a gas as it passes from the slightly higher pressure inside the tank to the lower pressure in the withdrawal line. The heat of vaporization will be extracted from the liquid hydrogen remaining within the tank. This cooling effect will reduce the pressure within the tank as the hydrogen is withdrawn. As this process is continued, as when driving the automobile, the pressure will become too low for proper withdrawal of the hydrogen. To counter this effect, a small electric heater is placed within the inner tank. When the pressure becomes low, the heater will turn on and slightly warm the hydrogen to provide proper withdrawal pressure. When the tank is in use, the cooperative effects of cooling by vaporization and the heater will serve to keep the hydrogen tank at the proper operating pressure. At the end of a trip, the tank will be stabilized at a temperature and pressure suitable for allowing the car to stand unused.

203 Williams, Laurence O., "Hydrogen Power", Pergamon Press Inc., Maxwell House, Fairview Park, Elmsford, New York 10523, 1980

LIQUID HYDROGEN

VACUUM SUPERINSULATION

EXPANSION VALVE-

Figure 7.1 Vacuum Jacketed Cryogenic Liquid Storage Tank

Suitable for Storage of Liquid Hydrogen on a Vehicle

GASEOUS HYDROGEN

GAS OUTPUT k LIQUID FILL LINE

LIQUID HYDROGEN

VACUUM SUPERINSULATION

EXPANSION VALVE-

ELECTRIC HEATER

Figure 7.1 Vacuum Jacketed Cryogenic Liquid Storage Tank

Suitable for Storage of Liquid Hydrogen on a Vehicle

The tank will be operated for maximum use of the cooling potential of the liquid hydrogen. When gas is withdrawn, the pressure will drop in the withdrawal line. This drop in pressure will allow liquid hydrogen to flow from the tank through the vaporization valve. As it vaporizes it absorbs heat from the liquid hydrogen remaining in the tank. The gas will exit from the tank at a temperature of about 25 Kelvin. After leaving the tank, the cold hydrogen will pass through a heat exchanger where it will pick up heat from the automobile's cooling system. In winter, the heat to warm the hydrogen will be supplied by waste engine heat. In summer, the heat will come from the passenger compartment. Used in this manner the cold hydrogen can aid in providing the cooling necessary for comfortable air conditioning. Hydrogen warmed to about ambient temperature will be piped to the engine.204

The cooling potential of the hydrogen can be used to augment the air conditioning system. The amount of cooling available will depend on the overall efficiency to the automobile. In a low efficiency automobile, much hydrogen must be vaporized for each kilometer of travel and a lot of cooling potential will be available. In a highly efficient automobile, only a modest amount of hydrogen will be vaporized per kilometer and a secondary cooling system will be required. The use of potential cooling from hydrogen may allow the development of an air conditioning system that does not use fluorocarbons. The elimination of fluorocarbons from the air conditioning systems will eliminate their leakage into the atmosphere. Atmospheric fluorocarbons, part of which comes from leakage out of automobile air conditioning systems, are implicated in the destruction of the ozone layer that protects us from the ultraviolet radiation of the sun. This is another; abet minor, contribution to environmental protection from the use of hydrogen.

204 Williams, Laurence O., "Hydrogen Fueled Automobiles Must Use Liquid Hydrogen", Cryogenics, Vol. 13, No. 12, December 1973,

Page 693

The outer jacket of the liquid hydrogen tank is designed to hold the vacuum and resist impact damage. Several construction techniques are suitable for its construction. The requirement that the tank be vacuum tight is best satisfied by welded metal construction. Because the outer tank in not subject to any unusual thermal conditions, almost any common construction metal and many structural plastics are suitable. Very lightweight tanks have been fabricated with a thin metal shell to provide a hermetic seal and a Fiberglas-plastic outer layer to provide stiffness and strength. The tank must have sufficient strength and stiffness to support the outside air pressure and protect the tank from impact damage. Fiberglas composite tanks can be designed to be highly resistant to impact damage. The outer tank must be equipped with tie points for attaching it to the automobile frame and a penetration point for entry of the coaxial fill and withdrawal lines.

No matter how well designed, a small amount of heat will leak through the walls of the tank. The heat leak will cause the pressure in the tank to slowly rise. Under most circumstances, the pressure will remain below the upper limit because of the cooling during its most recent use. When the automobile is not used, it will take several days for the pressure to rise to the upper pressure limit of the tank (something of the order of 5 atmospheres). Automobiles are seldom allowed to stand without use for long periods but, when this occurs, safe venting of the tank is necessary. Failure to vent can result in the rupture of the internal tank if the pressures increase above the tank's rated burst pressure. To ensure safety, hydrogen will be vented to reduce the pressure in the tank 5% to 10% below the upper pressure limit. The venting will cause liquid hydrogen to boil reducing its temperature. The combined effect of reduced pressure and cooling will allow the tank to remain unvented for a period much longer than the time required for venting.

A number of schemes have been suggested to ensure safety during venting. The simplest is to vent extremely slowly. Hydrogen has the highest diffusion rate of any gas and a slow vent rate will allow the gas to diffuse away without allowing a combustible mixture anywhere except at the tip of the vent pipe. The argument against this scheme centers on the consequences of the ignition at the vent and of the storage of the venting automobile in a tightly sealed confined space where a dangerous concentration of hydrogen could accumulate.205

Thoughtful location of the vent pipe on the automobile will make the probability of ignition at the vent remote. Good design will also include consideration that if ignition occurs there will be no damage. For example, the vent with a heat shield can be placed under the car near the center. This is common practice today with catalytic converters that also get quite hot. This arrangement of the vent will make ignition remote and consequences of ignition benign.

Venting, without ignition, into a tightly closed garage could eventually result in the buildup of a combustible mixture. It would require a remarkably tight garage and a good deal of time, but this remote hazard is the possible disadvantage of slow venting. Slow venting combined with a catalytic burner is another scheme that has been proposed. With this proposition, the vent is equipped with a small cage containing a catalyst capable of igniting air-hydrogen mixtures. The vent outlet is arranged so the out-flowing hydrogen contacts the catalyst and ignites. The catalyst cage will be designed with a large surface area to allow dissipation of the heat of the oxidizing hydrogen. The size will be selected to ensure the cage cannot start anything else on fire. With this scheme, an automobile parked for a long period of time will produces a small amount of heat and steam when venting hydrogen. The hydrogen flow could be balanced so that the vent became no hotter than today's catalytic converter.

205 Arvidson, J. M., Hord, J. and Mann, D. B., "Efflux of Gaseous Hydrogen or Methane Fuels from the Interior of an Automobile" U. S. Department of Commerce, National Bureau of Standards, Technical Note 666, March 1975

An intriguing system involves the venting of the hydrogen through a small air-hydrogen fuel cell. The fuel cell induces hydrogen to react with the oxygen of the air to produce an electric current (other automotive uses of fuel cells will be discussed later in this chapter). Use of the fuel cell allows the venting of hydrogen to produce a small amount of electric energy. This energy can be used to keep the storage battery of the automobile charged. As you will see something similar to this has already been incorporated in the BMW 750hL hydrogen fueled automobile. This scheme will have the double advantage of providing a safe hydrogen vent and keeping the battery fully charged when the automobile is not in use. Small fuel cells suitable for this service are currently available.206

Simple venting and venting through a catalyst are both available without the discovery of any new scientific principals. They both will require hardware development. Both will be easy to apply and the cost will be low. The use of the fuel cell will result in a more costly installation and will require a greater amount of development work, but will offer operational advantages for the vehicle. Any of these can be used to provide a safe method of preventing the parked automobile from being a safety hazard.

The small heat leak into a well-designed automotive liquid hydrogen tank will result in a loss of 0.1% to 1.0% of the liquid per day when the automobile is not in use. If the owner of a vehicle filled the tank, parked the vehicle and left it unused for an extended time, the liquid hydrogen tank would reach venting pressure in 3 to 6 days and would run out of fuel after about a year. If the tank were only partly full, it would boil dry sooner. A hydrogen tank completely empty of liquid and warmed to ambient temperature will still be filled with hydrogen gas at 5 atmospheres pressure. This small amount of gas may be enough to drive the auto to a filling station; if not, the operator must request a service call from an appropriately equipped service truck. Liquid hydrogen cannot be transported in a simple metal can. The consequence of allowing the vehicle to run out of fuel will be a visit from a truck especially equipped to handle liquid hydrogen refueling.

For the operator, refueling a liquid hydrogen fueled automobile will be substantially the same as refueling current vehicles. The vehicle will be driven alongside a dispenser. A flexible hose from the dispensing unit will be attached to the fill port of the vehicle. The dispenser will be activated and the hydrogen tank on board the vehicle will be filled with the requested amount of liquid hydrogen. When the vehicle tank is properly filled (a full or partial fill is possible) the dispenser will signal the operator to remove the flexible hose. The operator will disconnect the hose, return in to the dispenser, pay for the fuel and drive away. The lapse time required for the refueling will be much the same as is experienced in refueling current vehicles; however, the design of the refueling dispenser will be more complex.207

When a closed tank is filled with a cryogenic liquid, the gas in the tank must be vented to prevent a dangerous pressure increase. To provide venting capability a double line is required to refuel a liquid hydrogen tank. One line will deliver the liquid fuel and a second collects the gas displaced from the tank. The pipes carrying the liquid hydrogen and hydrogen gas must be protected from contact with the air because its temperature is below the liquefaction temperature of air. If the cold pipe is exposed to air, it will be instantly covered by water frost. The frost will cool further and liquid air will condense on the surface. The liquid air can drip from the surface causing a freezing hazard and the liquid oxygen in the liquid air might start a fire or cause an explosion. This is a safety hazard. The

206 http://www.fueicellstore.com

207 http://www.press.bmwgroup.com

heat resulting from the condensation of the air on the outside of the line will make the hydrogen inside the line boil. Boiling of the hydrogen will cause pressure surges and interfere with the transfer of the liquid hydrogen.

As BMW has shown, care in design can provide a solution to the problem of transferring liquid hydrogen. The liquid line are be insulated by placing it coaxial inside the gas return line from the tank. An outer covering of thermal insulation in turn protects the gas return line. It is also be necessary to include a small vacuum pipeline from the dispenser to the interface between the fill line and the fill receptacle on the vehicle. These various lines will be incorporated into a fill line about 6 cm in diameter. Figure 7.2 shows BMW's excellent answer to this design problem.

Figure 7.2 BMW Liquid Hydrogen Refueling System

Picture supplied by BMW of North America

Figure 7.2 BMW Liquid Hydrogen Refueling System

Picture supplied by BMW of North America

The super-cold liquid hydrogen fuel (-20 Kelvin, -423┬░ F) requires a special refueling that can be performed without human intervention. The 750hL also uses a fuel cell in place of the battery to provide electrical power.

The operation of this refueling system is as follows

1. The dispenser will be activated.

2. The fill line from the liquid hydrogen dispenser automatically connects to the vehicle tank.

3. The dispenser will automatically determine if the connection is proper, by evaluating conductivity, position of micro switches and similar factors.

4. If the connection is faulty, the dispenser will signal the vehicle operator to adjust the fill line connection.

5. When a proper leak tight joint has been verified the dispenser will evacuate the air from the joint interface and all portions of the delivery system experiencing the low temperature of the liquid hydrogen.

6. After a moment, when a proper vacuum condition is obtained, the valves on the dispenser and the fuel tank will open and liquid hydrogen flow will be initiated.

7. The gas displaced from the tank will flow up the outer coaxial line to the dispenser for liquefaction or disposal. Flow of liquid hydrogen will continue until the automobile tank is full.

8. The automobile fuel gauge will detect when the tank is full and signal the dispenser to automatically stop hydrogen flow.

9. The valves sealing the tank and the fill line will be closed and the fill line will retract.

10. The vehicle operator will pay the bill and drive away.

The internal operation of the liquid hydrogen dispenser will be significantly more complex than the operation of the current gasoline pump. Fortunately, the actions performed by the vehicle operator will be much simpler than that encountered in refueling today's automobiles.

The liquid hydrogen fuel storage system used on the private automobile will cost more to manufacture than the simple steel or plastic tanks used as current gasoline fuel tanks. This increased cost is a result of both the greater complexity of the tank and the requirement it be made with close tolerances. In the purchase price of an automobile, these costs will largely be offset by a reduction in the cost of the emission control equipment. The combustion of hydrogen is so clean there is no need for any complex emission controls.

Figure 5.1 in Chapter 5 showed the relationship between the production of polluting emissions and the air-hydrogen mixture ratio; however, it is useful to review this with specific reference to hydrogen performance in automobile internal combustion engines. The hydrogen fueled internal combustion engine can be operated in a manner that produces very little air pollution. Many of the air pollutants currently emitted from an automobile are carbon compounds. The list includes unburned hydrocarbons, carbon monoxide, aldehydes, ketones and carbon dioxide. Unlike current fuels, hydrogen contains no carbon and its combustion cannot produce any carbon compounds.

All crude oil contains sulfur compounds. The amount varies and the refiners strive to reduce the sulfur content of the fuels they sell. As hard as they try, it is not possible to remove all the sulfur. When the fuel is burned the sulfur is converted to sulfur dioxide, one of the major contributors to acid rain. Hydrogen contains no sulfur and its combustion produces no sulfur dioxide.

In all high temperature, combustion processes a small portion of the oxygen and nitrogen in the air react to produce nitrogen oxides. This is the source of the other major component of acid rain, nitric acid. Depending on the ratio of hydrogen to oxygen, hydrogen burning can also produce nitrogen oxides. If the ratio of hydrogen to oxygen is adjusted to provide a slight excess of hydrogen, nitrogen oxides are not produced. This is a result of the much greater chemical affinity of hydrogen for oxygen, than nitrogen for oxygen. It does not take a large excess of hydrogen to achieve this effect. The mixture ratio for complete reaction is two volumes of hydrogen to one volume of oxygen. A 1% excess of hydrogen is sufficient to suppress the formation of the nitrogen oxides as shown in Figure 5.1 in Chapter 5.

Excess fuel is used to suppress formation of the nitrogen oxides in current low emission automobiles. When an excess of gasoline is used to suppress the formation of nitrogen oxides the amount of unburned hydrocarbons and carbon monoxide is increased. The modern low emission engine uses a small excess of fuel to suppress the formations of the nitrogen oxides and then adds a catalytic converter to oxidize the unburned hydrocarbons and carbon monoxide at a temperature too low to reform the nitrogen oxides. If sufficient excess fuel is used to totally suppress the formation of the nitrogen oxides then traces of unburned hydrocarbons pass unreacted through the catalytic converter. Current automobiles use a compromise with a little excess fuel to reduce the nitrogen oxides, but not enough to cause too large an increase in the level of polluting carbon compounds.

Unlike the release of unburned hydrocarbons, the release of a small excess of hydrogen will not result in any secondary chemical reaction that produces polluting substances. A little hydrogen is always present in the air because of biological processes and decomposition of water by the ultraviolet radiation from the sun. The ultraviolet radiation causing decomposition also causes the recombination of the hydrogen to produce water. The reactions that produce hydrogen and those that remove it are in balance and result in a hydrogen concentration of about 4 parts per million. Hydrogen added to the air, by its use as a fuel, will enter into this equilibrium reaction cycle without making any measurable change in the long-term concentration of hydrogen in the air.

The liquid hydrogen tank and refueling system described above will be suitable for any type of vehicle currently serviced by the standard gasoline station; such as, small or large trucks, farm equipment, construction equipment, private boats, etc. The vehicle user will find liquid hydrogen fuel requires about the same type of actions and the same level of skill as needed for the use of gasoline fueled vehicles. The future hydrogen fueled vehicle will emit essentially no pollution and will achieve this without the addition of performance robbing unreliable pollution control equipment that is costly and complex to maintain. Hydrogen combustion will produce little or no acid and no solid carbon or lead residues. As a result, well-designed hydrogen engines should last a long time and require little maintenance.

Finally, there is one small advantage to the liquid hydrogen fueled automobile. It will be very important to users living in cold climates. Liquid hydrogen is so cold in its own right that any temperature encountered in the environment is relatively hot. No matter how cold the weather, with proper lubricants, the hydrogen-fueled vehicle should start as if it were a warm day in summer.

We have examined the use of liquid hydrogen as a fuel for the private automobile powered by an internal combustion engine and found it is a satisfactory fuel from the users' standpoint; there are no insurmountable technical barriers to its use and it has several clear advantages over current fuels. These advantages are very low emissions without performance degrading pollution control devices, and favorable cold start characteristics. In addition, deaths by carbon monoxide poisoning are no longer possible.

The conversion of the current automobile engines to the use of hydrogen has been shown to be technological feasible.208 Figure 7.3 showed one of the BMW research vehicle converted to operate on liquid hydrogen.

Figure 7.3 BMW 750hL Hydrogen Powered Automobile

Picture supplied by BMW of North America

Figure 7.3 BMW 750hL Hydrogen Powered Automobile

Picture supplied by BMW of North America

As part of the BMW Group's Clean Energy initiative the 750hL represents a practical hydrogen powered automobile that can also, when necessary, run on Gasoline.

The BMW vehicles use internal combustion engines. They are used for over-the-road transport of visiting officials from the local airport to the company headquarters. This technology can be used for all the private automobiles and vehicles using automobile type engines such as, trucks, busses, private airplanes, and boats. There remains a group of fuel burning transportation and transportation related devices somewhat different from the automobile. These are: equipment powered by diesel engines and small engines powering equipment such as lawn mowers, chain saws, motor cycles and outboard motors.

Internal combustion diesel engines are used in a small number of automobiles, and in many trucks, off-road equipment, trains and boats. These engines can also be converted to hydrogen. The problems of these conversions are different than those encountered in an internal combustion engine equipped with a carburetor. In the diesel cycle, the fuel is directly injected into the cylinder near the time of maximum compression. The compressed air is hot enough to ignite the diesel fuel. It would seem reasonable that injection of high-pressure hydrogen could be substituted for the diesel fuel. Unfortunately, in the tests performed with compression ignition diesel engines, hydrogen does not

208 http://www.press.bmwgroup.com

reliably ignite. This reluctance to ignite when directly injected into the hot compressed air does not prevent the conversion of diesel engines to hydrogen fuel, but it adds some new requirements.209

Figure 7.4 An EIMCO Mining & Machine Co. Underground Mining Truck

Converted to Hydrogen Fuel Conversion by Hydrogen Components Inc., INCO, DRI, and Caterpillar Corp. Picture Supplied by Hydrogen Components of Denver Colorado

Figure 7.4 An EIMCO Mining & Machine Co. Underground Mining Truck

Converted to Hydrogen Fuel Conversion by Hydrogen Components Inc., INCO, DRI, and Caterpillar Corp. Picture Supplied by Hydrogen Components of Denver Colorado

In 1997 Eimco Mining Machinery Co., Of Salt Lake City, Utah combined with Hydrogen Components Co. of Denver Colorado, Denver Research Institute (DRI), and the International Nickel Co. (INCO) Toronto, Canada to demonstrate the conversion of an underground mining truck to hydrogen fuel. The intent was to demonstrate that use of hydrogen as a fuel would eliminate the diesel exhaust with its soot and toxic oxides of nitrogen and carbon. The piece of equipment had a Caterpillar Co. 7-liter diesel engine (Cat 3304) that had been converted to run on natural gas. A metal hydride storage system was fabricated. With a dual path method of backfire prevention and adjustment of the supercharger the engine was operated on hydrogen and demonstrated 100% of the rated power.

This hardware still exists at the National Institute of Occupational Safety and Health in Spokane, Washington. Testing showed that the nitrogen oxide production was much lower than when the engine was operated on diesel fuel and of course, there was no carbon dioxide, carbon monoxide or unburned hydrocarbons in the exhaust. It has been successfully operated in the first quarter of 2001. Figure 7.4

209 "Development of a Hydrogen Injector for Use in Hydrogen-fueled Diesel Engine Research", Proceedings of the Inter Society Energy Conversion Engineering Conference, August 25, 1986

shows this truck. Since the fumes from diesels are harmful to miners it is likely that hydrogen fueled mining equipment will have a bright future in the near term.

Almost all diesel engines have a glow plug type ignition system used in cold starting. It consists of a coil of oxidation resistant wire attached across the terminals of a plug designed much like a spark plug. When the engine is cold, a current is passed through this wire heating it to the ignition temperature of the fuel. When the cold fuel is injected, the hot coil encourages ignition until the engine is hot enough that compression ignition can be effected. When the engine warms to proper operating temperature, the current to the glow plug coil is cut off and the engine continues to operate on compression ignition. In conversion of the diesel engines to hydrogen, the injection system will be modified to provide hydrogen injection and the glow plugs will be upgraded to continuous service to provide the ignition impulse required for ignition of hydrogen.

The fuel efficiency advantage of the diesel cycle derives from the high compression ratio of the engine (15 to 25) and not from the compression ignition. The use of direct hydrogen injection with a full time glow plug ignition system will not reduce the thermodynamic efficiency of the diesel engine in any way. It will eliminate the black cloud of smoke produced by the diesel engine when operating under high load.

For most heavy equipment using diesel engines, the problems associated with the storage of the liquid hydrogen are less critical. The underground equipment shown above used metallic hydride storage. Heavy equipment usually has sufficient on board space to accommodate a large liquid hydrogen tank. Fuel boil off rates are low, for large tanks. Heat leaks through the surface of a cryogenic storage tank in proportion to the surface area of the tank. The rate of boiling, or vaporization, is related to the volume of the tank. Doubling the linear dimensions of a tank increases the surface area by a factor of 4 and the volume of the tank by a factor of 8. Because of this ratio, the bigger a tank the lower the vaporization rate as a percentage of the total liquid hydrogen stored in the tank.

Equipment with small internal combustion engines, with fuel tanks of less than 10-liter capacity (motorcycles, outboard boat engines, lawn mowers and the like) may never be converted to liquid hydrogen. The problem in this case is not with the engine, but with the storage and refueling. Small liquid hydrogen tanks will show high heat leaks and thus, poor fuel storage efficiency. The technology involved in transferring the liquid hydrogen will be difficult to miniaturize for use in small engines. Fuel Cells will provide the solution to small equipment operations with hydrogen as the fuel. Fuel cells are so efficient that much less fuel must be stored to accomplish a task. This large reduction in fuel makes high-pressure gas storage feasible.

The international company, Shell Oil Co., performed a total cycle analysis of the greenhouse gas produced by a series of current and suggested automobile propulsion systems. As reported in New Scientist 210 Shell's study shows that many of the suggested systems do not offer a significant advantage over current technology. For example when the total process of making hydrogen from fossil fuel and using fossil fuel energy to liquefy it, the hydrogen fueled internal combustion engine actually deposits more green-house gas in the atmosphere than is produced by today's automobiles. These comparisons are shown in Figure 7.5. Two thines were missine from this study. First, as mentioned elsewhere this book, making hydrogen from fossil fuels is meretricious. Hydrogen produced from fossil fuels will simply continue the addition of greenhouse gas to the atmosphere. No honest promoter of new technologies envisions fossil fuels as the future source of hydrogen. Second,

210 Hamer, Mick, "It's time to scrap the gas Guzzlers", New Scientist, 17 March 23, 2001 page 19

if one properly considers systems using hydrogen from a non-fossil source, both the internal combustion engine and the fuel cell systems would emit essentially zero greenhouse gas. Internal combustion engines burn a little oil, say a liter in 20,000 kilometers. This leads to an emission rate of 0.05 grams per kilometer. The hydrogen fuel cell automobile emits only water. This is shown in line 1 and 2 on Figure 7.5. Lines 1 and 2 are NOT presented in the Shell study.

Figure 7.5 Comparison of the Greenhouse Gas Emitted by Automobiles

Considering the Total Fuel Cycle. Items 3 through 12 Used Fossil Fuels as the Source of Hydrogen - Shell Inc. Study

Figure 7.5 Comparison of the Greenhouse Gas Emitted by Automobiles

Considering the Total Fuel Cycle. Items 3 through 12 Used Fossil Fuels as the Source of Hydrogen - Shell Inc. Study

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