Managing the temperature demands of a catalytic converter regeneration (Regen) event is a growing concern for mass transit engine service operators. Extremely high temperatures associated with Regen events can pose dangers for vehicle exhaust (VE) systems and their users. Everything from fan capacity to the velocity of air in the flexible hoses that duct extremely high temperature exhaust fumes away from diesel engine maintenance bays needs to be able to mitigate temperatures that can exceed 1,600 F and cause safety problems.
“We were concerned that if the engine exhaust system went into the Regen mode when the vehicle was in the garage, the existingexhaust hoses would not be able to withstand the high temperature and may cause a fire,” says Dave Varner, director of Bus Maintenance at the Maryland Transit Administration (MTA). So, what did Maryland do? “We changed all exhaust hoses to high-temperature,” Varner says. A complete facility-wide upgrade of MTA’s engine exhaust systems came at a time when the transit system was able to replace all flexible exhaust hoses and upgrade VE systems with those capable of ducting the 1,500 F and higher temperatures, and MTA did so.
CEOs of transit agencies are directing their safety managers and facility architects to look into how best to accommodate changes created by new, higher-temperature engines and to meet the requirements of new regulations. Private bus garage operators, too, are looking for technical answers to the extremely high heat, safety and ventilation issues that arise from catalytic converter regeneration that occurs during planned maintenance operations.
OEMs that offer full vehicle exhaust systems and design services to bus and transit authorities are quick to point out that hoses capable of handling extremely high temperatures are just a part of the solution for managing new, high-performance engine exhausts. “Often, vehicle exhaust systems are not designed by a person in our industry,” says Fred Imming, president of Car-Mon. “Unfortunately, service managers want to use what they already have, as much as possible,” Imming says.
“They really need to look beyond components to systems,” he suggests. “Vehicle exhaust systems require a systems professional, not just a consulting engineer with HVAC experience. The difference is that we are dealing with contaminated air versus standard air for venting.”
Sizes, Fans and Pressures
System sizes, the number of drops, venting diameters, the right fans, maintaining correct flow rates — they all have to be considered, Imming says. “The best counsel that I can suggest is, you really need to contact a person familiar with the requirements and materials available, and actually determine which system fits your individual needs.
“You need to evaluate system performance in general. We’re systems guys, not component guys,” Imming says of Car-Mon and similar OEMs companies.
Systems OEMs Share Views on Extreme Temps
Kyle Jefferson, VP of sales and engineering at Ventaire, echoes the need to have exhaust fans properly sized to ensure that VE systems are not compromised by extreme temperatures, and he goes a step beyond. “For existing systems, a portion of all of the flexible hose may need to be upgraded to one that carries a higher temperature rating.” Are there ways to economize?
“Yes,” says Jefferson. “The first 10 feet of flexible hose takes the brunt of the heat since the exhaust gases cool quickly after they enter the exhaust capture system. Hoses with different temperature ratings can be spliced together with the section near the inlet carrying the highest temperature rating,” he explains. “We supplied a system for a bus manufacturer that utilized 10 feet of hose rated to 2,010 F coupled to 25 feet of hose rated to 1,200 F,” Jefferson says to further illustrate the example.