Mercedes Bringing Stratified-Charge V-6 to U.S.
With the new stratified-charge application, the turbocharged 3.0L V-6 will continue to employ direct fuel injection, but the injectors have been redesigned to spray under higher pressure later in the intake stroke, just before compression.
June 27, 2016
CARMEL BY THE SEA, CA – Mercedes-Benz will bring to the U.S. market later this year a V-6 production engine employing a stratified-charge fuel injection system that is expected to singlehandedly boost fuel economy up to 6%.
The automaker is not yet able to identify the vehicle, but the engine is a modified version of the stout 3.0L twin-turbo V-6 appearing now in the C-Class, SLC roadster, GLE CUV and GL SUV. That engine was included in the 2016 Wards 10 Best Engines competition, evaluated in the 362-hp C450 AMG sedan.
With the new stratified-charge application, the 3.0L V-6 will continue to employ direct fuel injection, but the injectors have been redesigned to spray under higher pressure later in the intake stroke, just before compression, and the fuel is shaped to arrive in certain areas within the cylinder to optimize combustion.
This strategy makes for an air-fuel mix within the chamber that is much leaner than with a conventional homogeneous-charge system that fills the chamber more uniformly before combustion, says Bart Herring, general manager-product management at Mercedes-Benz USA.
Herring says Mercedes already has some vehicles on European roads using stratified-charge combustion.
“The advantage is you can get the same bang with less fuel,” Herring tells WardsAuto during the media launch of the all-new Mercedes E-Class. “You want to direct the fuel because there are certain hot spots in the combustion chamber where it’s more advantageous to have fuel.”
Herring says Mercedes already has a limited number of vehicles on the road in Europe using the stratified-charge strategy, and that this initial application in the U.S., if successful, could lead to widespread usage in all gasoline engines.
He could not specify the added cost of the technology, but Herring says the potential to improve fuel economy between 4% and 6%, without reducing horsepower or torque, is enormous. He expects customers won’t even know the new technology is at work but should notice impressive fuel economy.
“Everyone is fighting for a quarter percent, a half percent or 1% in terms of fuel economy (improvement),” he says. “This could be 6%. You are getting the same bang with a lean-burn mix.”
Herring says he is not aware of any other automaker using this technology in U.S. production vehicles.
However, Honda achieves a similar stratified-charge effect with its well-regarded 2.4L direct-injected 4-cyl., which allows for a richer air-fuel mixture near the spark plug for easy ignition, maximizing efficiency at low engine speed and helping reduce emissions in cold temperatures.
Mercedes is launching an all-new E-Class sedan, soon to be followed by a wagon and convertible, as well as a high-performance E43 AMG sedan that will use the 3.0L twin-turbo V-6. However, Herring says the E43 AMG will not have the stratified-charge system.
The Mercedes technology will arrive as the U.S. has mandated cleaner ultra-low sulfur gasoline, which will ease some of the exhaust aftertreatment challenges associated with stratified charge.
Much of California and parts of the East and West Coasts, as well as many metropolitan markets fighting smog, already have ultra-low sulfur gasoline, and the migration is expected to be complete nationwide by 2018, Herring says.
In this first vehicle application, Mercedes is designing the emission-control system to handle both types of gasoline. However, even with cleaner fuel, a stratified-charge system likely will require a trap to burn off excess oxides of nitrogen that result in lean-burn combustion, Herring says.
Besides the new fuel injectors, Herring says the system will require new software to run the system.
Exactly when the turbo V-6 arrives with stratified charge remains unclear because of unpredictability in the EPA approval process, he says.
“Certification is now a big black box,” he says. “You throw a car in, and you used to say it will come out on Tuesday. Now, it could be five months from now.”
Herring describes stratified charge as an example of taking technology within a conventional powertrain to the absolute limit as part of a multifaceted approach to meet fuel-economy and emissions mandates that will intensify in coming years.
“We have some great things coming in that realm,” he says. “We are looking forward to what (stratified charge) brings to the road in terms of fuel economy and also still giving that same customer experience and great power – all those things they are expecting.”
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