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Metal-hydride system heats catalytic converters
August 28, 1995
4 Min Read
Ringwood, NJ--Automobile catalytic converters are heated electrically upon cold start to help bring the catalyst to "light-off" temperature (300 to 350C). Because the catalyst converts unburned hydrocarbons into non-toxic water and carbon dioxide only after it reaches light-off temperature, heating the catalyst reduces pollution during the first few minutes of vehicle operation.
Using electricity to heat the catalyst loads a vehicle's battery and charging system. Also, electrical heating is too slow to meet proposed low-emission vehicle (LEV) and ultra-low-emission vehicle (ULEV) standards, which are 70% and 80% cleaner than 1995 standards.
This new metal-hydride cold start heater (CSH) generates three to four times more heat than electrical heaters, enabling it to bring catalysts to light- off temperature in seconds. Further, the device does not load a car's electrical system. The reversible exothermic/endothermic chemical-reaction system reportedly lowers automobile hydrocarbon pollution as much as 80%, surpassing LEV standards and meeting ULEV standards.
Ergenics Inc. is currently marketing its patent-pending CSH technology to automobile builders. The company plans to design versions of the nominally 5-lb, 12-inch-long CSH system for small displacement engines, as well as for six-cylinder and V-8 engines. Analysis indicates that the technology will cost about $100 to $150 per car, some $150 to $200 less per car than current electrical systems, according to Ergenics.
The metal-hydride CSH works by placing an exothermic reaction in the path of the exhaust gas, ahead of the catalytic converter. Each heater consists of two beds connected by a solenoid valve from Kip Valves, Farmington, CT. One bed, a low-temperature alloy "source" bed, is contained within an aluminum bottle from Parker-Hannifin's Cliff Division. It operates at about atmospheric pressure. The second, a proprietary high-temperature alloy "heater" bed, is contained within stainless steel coils.
When the solenoid valve opens, hydrogen escapes from the source bed's metal hydride (MmNi4.3Al0.7). The heater bed's low-pressure alloy then absorbs the hydrogen. This exothermic reaction raises the heater bed's temperature dramatically, and brings its coils to 400C in less than five seconds.
About 20 seconds after engine startup, the solenoid valve closes. As the engine warms up, its exhaust reaches temperatures ranging from 500 to 650C. That stream of hot gas liberates hydrogen from the heater bed's metal hydride. After separating from the hydride, the hydrogen returns to the source bed through a check valve, and awaits the next startup cycle. Ergenics says the reversible, self-contained CSH consumes just 6W--to operate the solenoid valve. The company estimates a 25,000-start or 100,000-mile lifetime (the latter specification is a federal requirement and applies to all emission-control systems).
Although the CSH is elegantly simple, "we've had to overcome a lot of problems," says Mark Golben, the CSH's principal designer. "We had to develop an alloy impervious to high temperatures, and find a way to rapidly transfer heat from the heater bed's metal hydride to the exhaust gas." Because Ergenics has a patent pending on their hydride production process, Golben won't say how the firm made the high-temperature alloy. But he claims Ergenics' proprietary metal alloy resists the tendency of hydrides to break down into a stable alloy, which would destroy the material's reversible-process potential.
Normally, smaller tubing restricts flow in heat-transfer systems like air conditioner coils. But hydrogen flows far more easily than Freon(TM). So, contrary to conventional thinking, "I realized that there was no penalty associated with going to a smaller size tube," says Golben. By using 24 ft of 1/8-inch-diameter stainless-steel tubing for the heater-bed coil, he made the coil's surface area/volume ratio about four times greater than that of coils that use .50-inch-diameter tubing. Naturally this increase in surface area quadruples the coil heat-transfer rate.
In tests, the CSH delivered 50 kW to a test vehicle's exhaust gas, far surpassing the 3 to 12 kW produced by conventional electrical heating systems. According to Ergenics, testing of the CSH by a respected national labratory conformed to Federal Test Procedures. It demonstrated that using the CSH resulted in non-methane hydrocarbon emissions of between 0.019 and 0.026 gm/mile--which corresponds to ULEV performance.
Because the CSH reaction involves only one gram of hydrogen, and because the hydrogen exists within the system at sub-atmospheric pressure, there is no danger of a hydrogen release. Inevitably, some of the system's hydrogen will migrate through the containment.To offset this unavoidable loss of working fluid, and also to guarantee that proper operation of the device will be ensured throughout its lifetime, Ergenics uses twice the quantity of hydrogen needed by the process.
Additional details...Contact Philip A. Burghart, Ergenics Inc., 247 Margaret King Ave., Ringwood, NJ 07456, (201) 962-4325.
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