Super Chief Tri-Flex Fuel V10 Engine
Those who enjoyed the “Mad Max” movies but wondered in amazement how a belt-driven supercharger could be turned off while the engine kept running will appreciate the V10 engine found in the Ford F-250 Super Chief concept truck.
Designed to burn three different fuels — hydrogen, gasoline and E85 ethanol—the Tri-Flex engine features a twin-screw supercharger that turns when running hydrogen. On gas, the boost isn’t needed, so a clutch pack mounted on the blower’s snout disengages the belt drive. It’s a rather seamless operation switching from hydrogen to gas or E85 on the fly, but engaging the supercharger for hydrogen must be done at low speed.
The Tri-Flex engine is based on the 6.8-liter hydrogen V10 engine that will be utilized in about 50 E-450 shuttle vans to be distributed to fleets in Florida and Canada. The engine and van were shown at least year’s Detroit Auto Show and used to shuttle the press to various events. Now the van will go into limited production for public use as a way to demonstrate hydrogen potential. Of course, the hydrogen V10 is based on the Triton V10 that’s been in the Super Duty for years. And with Ford’s experience in building about 1.6 million flex-fuel vehicles that can run on gas or E85, powertrain engineers challenged themselves to combine all three technologies on one engine.
A dual fuel system is the most obvious clue to the engine’s unique ability. Two different fuel rails and two sets of fuel injectors are clearly visible. The gas/E85 injectors are closest to the intake valve the while hydrogen injectors are just a little inboard. Supplying hydrogen are 10,000psi Type 4 tanks constructed of a polymer liner surrounded by a carbon-fiber overwrap. There is enough capacity for a 500-mile range while running on hydrogen.
“With hydrogen we run very lean,” explains Bob Natkin, a chief engineer on the project. “Stoicmetric for a gas engine is 14.7:1 and for a hydrogen engine it’s 34.2:1. With gas you can lean it out to 24, maybe 26:1 before you get misfire. We can run hydrogen out to 280:1. So there’s a very broad combustion range we can take advantage of.”
There are only extreme minute amounts carbon emissions in a hydrogen engine due only to whatever oil finds a way into the combustion chamber. But NOx is still an issue. As the engine leans out, NOx is reduced but so is power. That’s why the supercharger is needed. By adding about 18 pounds of boost, horsepower and torque close in on the gas levels. A Triton V10 is rated at 310 horsepower with 425 lb-ft of torque. On hydrogen, the Tri-Flex engine is rated at 250 horsepower with 400 lb-ft of torque.
“We could go higher on power but then we need a bigger NOx trap,” says Natkin.
Driving this type of technology helps make a current business case for developing a hydrogen infrastructure and pave the way for fuel-cell vehicles and a complete renewable hydrogen fuel economy. The upside is that very little has to be done to an existing gas engine to run hydrogen.
“It’s a conventional technology for a very unconventional fuel,” says Natkin.
Inside, the Tri-Flex engine looks normal. It runs a 9.4:1 compression ratio and cam changes are not necessary between fuels. The spark plugs are a cool-temperature racing type and the ignition is set up to prevent unnecessary spark events, especially during the exhaust cycle. Ignition timing is also much later than a gas engine, firing after TDC instead of before.
Throttle control in hydrogen mode can be done with fuel, like in a diesel, or with air through a throttle valve.
“We can do it both ways and we can pick and choose,” says Natkin.
“We can run open throttle and increase power with boost and air-fuel ratio.”
The main limiting factor to fine-tuning the engine is computer memory. Millions of calculations are needed to read the conditions and adjust the fuel and spark between the three different fuels. Even though computer modeling is helping engineers save time, considerable on-road testing is needed to adjust the numbers. Even the actual engine cost isn’t prohibitive.
“Typical powertrain cost under the hood, including transmission, is about $25 to $35 per kilowatt (1 horsepower is .746 kilowatt). With hydrogen it jumps about $5 more to $30 to $40,” says Natkin. “Where the cost comes in is the fuel storage.”
Engineers will monitor the E450 test fleets to update their computer models and test for reliability. Meanwhile, Ford continues to promote flex-fuel options in many of its vehicles, including the F-150 and is working to improve the availability of E85. In the future, a diesel-hydrogen engine could be developed.
“There have been discussions about that,” confirms Natkin. “I can’t tell you if it’s possible. I can’t tell you if it’s impossible. There would have to be considerable development work put into such a project.”