It’s true, “Necessity is the mother of invention.” It’s also true that even though non-conventional propulsion systems such as hybrid electric, fuel cells, and hydrogen fueled internal combustion engines are in their infant stage of development – good progress is being made. Furthermore, the effort to improve the performance of the internal combustion engine, especially as it pertains to the diesel engine, continues full-speed-ahead. And for those of us who are RV enthusiasts, research and development involving all of the above is finding its way into the kinds of vehicles we enjoy – SUVs, trucks and large bus-style vehicles. Few disciplines are progressing more rapidly than those associated with “how to propel a vehicle.” Efforts are being made to educate the public to “think outside of the box,” so we to can understand what’s going on inside these new black boxes. Several technologies are competing in this 21st century challenge. All technologies have something to offer. When the dust finally settles, a combination—or mix—of all of these technologies will probably propel tomorrow’s vehicles. In addition to pure-electric, hybrid-electric and fuel cell powered vehicles (which we’ll explain momentarily), conventional engines are being fueled using propane, compressed natural gas (CNG), ethanol (fuel made from corn or beats), liquefied petroleum gas (LPG) and even pure hydrogen, such as the Shelby Cobra being experimented with by the University of California, Riverside. The success that clean diesel technology has achieved is significant and the efforts to develop a near zero emission diesel engine, bodes well for its future. Equally important, but less visible, is the debate over the refueling infrastructures needed to support these new technologies. In other words, “How will the tanks and batteries of hydrogen, electric, compressed natural gas fueled vehicles be filled or their batteries charged?” Unless the end-user has safe and convenient access to refueling stations, the widespread acceptance of these next generation technologies is questionable. "When the dust finally settles, a combination- or mix- of all these technologies will probably propel tomorrow's vehicles." Yes, thinking outside of the box no longer means (as it did a decade ago) battery-powered golf carts or two-person electric cars for use around town. Reinventing, redesigning and refining the wheel as it pertains to propulsion systems, is touching virtually every corner of the transportation landscape. CLEAN
DIESEL ENGINE TECHNOLOGY So what are diesel engine builders doing to meet this challenge? Taking the NOx issue first, it’s important to understand that high combustion temperatures (the kind experienced in compression ignition, the diesel engine) create NOx. It’s a function of temperature and chemistry. To control the ignition temperature of the diesel fuel in the cylinders, air-to-air coolers are being used to reduce the temperature of the intake air after it’s compressed by the turbocharger. Second, a process called EGR (exhaust gas recirculation) is being used that takes some of the exhaust gas and recycles it back into the intake in place of ambient air. Combustion temperatures are lowered because the amount of oxygen found in ambient air is reduced by exhaust gas that can’t combust. Third, high-tech electronic fuel injection systems are being used that inject diesel fuel at different times during the compression stroke. This lowers the temperature by introducing several controlled events (combustions) throughout the stroke, instead of a single high temperature ignition at the top of the stroke. Even the shape of the combustion chamber is being experimented with as a way to shape and control diesel ignition. But to achieve full compliance by the year 2010, low-sulfur diesel fuel is an absolute must and a requirement. By lowering the sulfur content, catalytic converters that convert NOx into harmless gases, can be used in diesel engines the way they have been used in the automobile for the last 20 years. Refiners are required to begin delivering low-sulfur diesel fuel for vehicle use by mid-2006. Reducing PM (particulate matter) is also being achieved by state-of-the-art high-pressure fuel injection systems. When diesel fuel is delivered under high pressure (for example 6,000 p.s.i), the droplets delivered inside the combustion chamber are small (atomized), allowing them to be more completely surrounded by air, a condition that brings about complete combustion. Exhaust filters to trap PM are being tested. Research continues on best to clean or regenerate PM filters, once the buildup of soot reaches a specified level. Also, a device called a flow-through oxidation catalyst that reduces PM has been installed on 1.5-million heavy trucks with excellent results. Turbocharger designs are also being re-thought. One is called variable geometry. This allows the fuel to burn efficiently over a broad range of operating and performance demands. Another design is the electrically assisted turbocharger. During short periods of demand, such as passing and hill climbing (during fuel rich operating scenarios), this design boosts the amount of air going to the engine, thereby facilitating more complete combustion of the additional fuel being injected. Fuels such as compressed natural gas are also being experimented with for use in diesel engines. DIESEL-ELECTRIC
HYBRIDS One diesel-electric hybrid system being developed is the Allison Electric Drive Hybrid system. It is called a parallel system. “Parallel” means the electric motors are used to get the bus rolling and up to speed (electric motors yield lots of torque). When cruising speeds are reached, the diesel engine takes over and becomes the primary source of propulsion and the electric motors stop. When additional torque is needed, the electric motors return to service and both the diesel engine and electric motors share the job of propelling the bus. In the Allison Electric Drive Hybrid system, when the electric motors are propelling the bus, the diesel engine powers a generator that charges the batteries. Regenerative braking is a key element in any hybrid-electric package. What this means is that the electric motors (when the brakes are applied or the accelerator is released) instantly act as generators. As generators, they both slow the forward motion of the bus through the resistance created by an electric field and they help charge the batteries. THE
HYDROGEN FUEL CELL Hydrogen is passed through a Proton Exchange Membrane (PEM) that is made of exotic metals (gold and platinum). As the hydrogen atom reaches the PEM, the electron (a negative charge) is stripped away from the nucleus of the hydrogen atom, allowing the proton (a positive charge) to pass through the PEM. The electrons flow "The
storage of hydrogen requires tanks to hold the liquefied/ compressed
hydrogen gas. To eliminate carrying compressed hydrogen, a device
called a reformer is being developed."
around the membrane to the opposite side. As this current flows, it’s put through an inverter to power an AC motor that propels the vehicle. When the electrons and protons reunite on the other side of the PEM, they again form into atoms of hydrogen, with the hydrogen then combining with oxygen in the ambient air to form water vapor. The storage of hydrogen requires tanks to hold the liquefied/compressed hydrogen gas. To eliminate carrying compressed hydrogen, a device called a reformer is being developed. A reformer is like a miniature refinery, for it takes methanol or petroleum fuels and separates the hydrogen out of the molecules for use in the fuel cell. Another process being experimented with is the use of electricity to separate hydrogen and oxygen atoms in water so the hydrogen can be used in the fuel cell process. One real-world application of fuel cell technology is the ZEBus (Zero Emissions Bus). The ZEBus has a GVWR of 35,000 pounds and is powered by twin fuel cells and a 275-horsepower AC electric motor. It has been tested in Vancouver, Chicago and under summer driving conditions in Palm Desert. Thirty ZEBuses will now be put into service in ten Western European cities, with more units still to be delivered to California, Iceland, Brazil, China, India and Mexico. A second example of real-world fuel cell use is the Toyota’s FCHV-4, a Highlander SUV equipped with a 90kW fuel cell package that powers an 80kW motor. It produces 120-horsepower, can go 95 mph and has a cursing range of 155 miles. A nickel metal hydride battery works with the fuel cell, allowing such things as storage of energy from regenerative braking and the powering of secondary electrical systems. The FCHV-4 uses hydrogen stored in high-pressure tanks. The next generation Toyota fuel cell hybrid vehicle, the FCHV-5 (recently introduced at the Tokyo Motor Show) features a reformer that uses heat to vaporize methanol. The hydrogen extracted from the methanol is then used in the fuel cell and as the fuel to generate heat required by the reformer. Fuel cells have also been developed for
use as APUs (auxiliary power units) in heavy trucks. The APU
precludes the need to keep the diesel engine in a truck idling,
so that electrical systems can be kept powered up even when
the truck is rolling going down the road. What immediately comes
to mind is the applicability offered by the fuel cell APU in
the RV setting. A device like this could replace conventional
gensets with silent, emission-free power, where nighttime noise
(genset) restrictions at campgrounds forever become a non-problem
for RV enthusiasts. However, it’s important to remember (especially with technology) that out of challenge comes opportunity. Or, as implied in the opening statement, when necessity reaches a high enough level, it spawns creative responses that are useful, friendly and eventually accepted. J. Martin Kohler is a freelance writer baced in Northern, California, and author of several Lifestyles and Holidays features. |
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