As automakers and engineering consultancies focus on reducing the cost of running prototype vehicles and powertrains, there is a continuing move to more cycle simulation on engine testbeds, says Kevin Howell, Operations Manager of U.K. heat exchanger specialist, E.J. Bowman.
When trying to simulate vehicle cycles accurately on a test rig, it is essential that the fluid temperatures and warm-up profiles are precisely represented. Design of the heat exchanger is critical to help achieve accuracy, and stainless steel in-line ‘plate’ types have become the industry standard for cooling fuel.
“However, the growing introduction of ethanol into fuels has created new demands on heat exchangers which are traditionally brazed with copper materials,” states Howell. But the meeting of copper and ethanol is creating problems.
“In the U.K., Environmental Protection Agency (EPA) regulations already allow blended fuel to contain up to 10% ethanol and in February 2012, the EPA decided to pave the way for the sale of gasoline blended with up to 15% ethanol. Powertrain systems’ developers, manufacturers, and consultants are carrying out extensive research on ethanol-based fuels to assess their ability to meet increasingly stringent fuel-economy standards and engine performance requirements.”
Automotive customers based in the U.S. or U.K. customers wishing to sell vehicles in the U.S. are now testing fuels that are 85% to 100% ethanol, he explains: “But using ethanol in fuels, even in modest amounts, can cause copper to be leached into the ethanol and deposited onto the fuel injection system, with the risk of subsequent performance problems and failures.”
Ethanol attacks copper and removes any deposits with which it comes into contact. It is these that can cause fouling within the fuel injection system and possible engine damage. In response to customer concern, Bowman’s R&D team developed a totally new construction method incorporating a special, copper-free brazing compound for its patented stainless steel in-line plate heat exchangers. The company believes the application represents an auto industry first.
“Heat exchanger design is obviously focused on the optimal transfer of heat,” states Howell. “Bowman favors a design that dissipates heat efficiently via channeling the fuel around the maximum internal surface area of the unit.”
The company’s patented plate type heat exchangers comprise 316 stainless steel plates, two outer covers, and four connections, vacuum-brazed together to form an integral unit. “Unlike other plate heat exchangers, they have a unique internal flow arrangement, which enables the inlet and outlet connections to be located in line,” says Howell. “This means that they can be installed directly into the fuel line without the need to modify or re-route the pipework.”
Each fluid stream flows in series through alternate plates: “Consequently, the plate spacing is larger and internal velocities higher than is normally the case with this type of heat exchanger, thus rendering them less prone to fouling.”
Normally, the plates are brazed together via a copper shim but the use of ethanol has forced a re-think with the R&D program followed by an extensive in-house test program to prove efficacy and reliability up to 100% ethanol levels.
The new unit is now undergoing further testing by an independent automotive engine systems specialist to validate Bowman’s results and to provide real-time performance and reliability data.