Mercedes Says No Lean Burn Engines for U.S. Thanks to "Dirty" Fuel
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Mercedes Says No Lean Burn Engines for U.S. Thanks to "Dirty" Fuel
http://www.dailytech.com/article.aspx?newsid=21177
I found this to be an interesting way to increase fuel economy. Do other manufacturers do this already? I wonder how lean they push it considering a really lean engine is not a good thing.
C350 gets no lean burn V6 in U.S. (Source: Wards Auto)Too much sulfur in gasoline for the new MB tech
Green is a big deal in the U.S. today with many carmakers striving to improve fuel economy with their standard gasoline engines and bring hybrids onto the market to meet consumer demand and government regulations.
Mercedes would like to join in on the fun in the U.S. with its so-called "lean burn" engines. These engines are able to run a leaner air/fuel ratio that improves fuel economy and reduces emissions. The problem for Mercedes and fans of the vehicles wanting the most efficient engine available is that the gasoline in the U.S. has too much sulfur in it today for the lean burn engines to be offered here.
Mercedes notes that lean burn engines can operate with fuel that has up to 50 parts per million of sulfur. The problem is in the U.S. the EPA allows gasoline to have 80ppm at the refinery gate and 95ppm downstream. Mercedes-Benz VP for powertrain development Bernhard Heli told Wards Auto, "That’s definitely too much."
The reason the new Mercedes lean burn engines can't operate with high levels of sulfur is that the cars use a special trap to gather up the various oxides of nitrogen created during combustion and trap them from escaping into the environment. The high sulfur concentration would produce more of the oxides than the trap could handle.
Mercedes notes that the U.S. isn’t the only country with high sulfur concentrations. Sulfur is even worse in Africa and other developing nations. Heli said, "In the rest of the world, we do have a situation that we are right now forced whenever we develop new engines to have a (lean-burn) concept for gasoline engines for Europe, but we are not able to operate them internationally."
The lean burn engine will power the SLK roadster in Europe and the engine will come to the U.S. sans lean burn tech in the 2012 C350 sport sedan. It will be rated for 302hp and 273 lb-ft torque. The fuel economy is up 5% from the previous year to 21 mpg.
Green is a big deal in the U.S. today with many carmakers striving to improve fuel economy with their standard gasoline engines and bring hybrids onto the market to meet consumer demand and government regulations.
Mercedes would like to join in on the fun in the U.S. with its so-called "lean burn" engines. These engines are able to run a leaner air/fuel ratio that improves fuel economy and reduces emissions. The problem for Mercedes and fans of the vehicles wanting the most efficient engine available is that the gasoline in the U.S. has too much sulfur in it today for the lean burn engines to be offered here.
Mercedes notes that lean burn engines can operate with fuel that has up to 50 parts per million of sulfur. The problem is in the U.S. the EPA allows gasoline to have 80ppm at the refinery gate and 95ppm downstream. Mercedes-Benz VP for powertrain development Bernhard Heli told Wards Auto, "That’s definitely too much."
The reason the new Mercedes lean burn engines can't operate with high levels of sulfur is that the cars use a special trap to gather up the various oxides of nitrogen created during combustion and trap them from escaping into the environment. The high sulfur concentration would produce more of the oxides than the trap could handle.
Mercedes notes that the U.S. isn’t the only country with high sulfur concentrations. Sulfur is even worse in Africa and other developing nations. Heli said, "In the rest of the world, we do have a situation that we are right now forced whenever we develop new engines to have a (lean-burn) concept for gasoline engines for Europe, but we are not able to operate them internationally."
The lean burn engine will power the SLK roadster in Europe and the engine will come to the U.S. sans lean burn tech in the 2012 C350 sport sedan. It will be rated for 302hp and 273 lb-ft torque. The fuel economy is up 5% from the previous year to 21 mpg.
I found this to be an interesting way to increase fuel economy. Do other manufacturers do this already? I wonder how lean they push it considering a really lean engine is not a good thing.
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Re: Mercedes Says No Lean Burn Engines for U.S. Thanks to "Dirty" Fuel
The systems all have cut-off points for load and RPM - lean burn only works on a very narrow band of conditions. Even then, the trade-offs are noticed - the engines are more expensive, the O2 sensors cost a fortune, and warranty costs were substantially higher and were all very difficult to troubleshoot.
With today's more sophisticated controls systems, the hardware is simpler and easier to manage. As the next generation of economy engines comes around (HCCI over current DI) we'll see lean burn come back into the fold.
FWIW a 2000 Civic was rated 32/37mpg (now 27/33) and a Civic HX was rated 35/43mpg (now 30/39).
I'm guessing (at the time) the warranty costs and upfront costs to manufacture and price to consumers could not justify the mpg increase - which lead to their decline and disuse.
And I'm guessing if Mercedes *really* wanted to, they'd have the car here and are just making excused. Honda, Nissan, and Toyota were able to do it 15 years ago. And Chrysler had a lean-burn carburetor system nearly 30 years ago!
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Re: Mercedes Says No Lean Burn Engines for U.S. Thanks to "Dirty" Fuel
I'm pretty sure a lot of late 80's/early 90's vehicles, especially cars like the CRX had lean tuning under certain conditions. I think I read they had to cut back on that to combat NOx. Burning too lean causes higher combustion chamber temps which causes NOx to rise.
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Re: Mercedes Says No Lean Burn Engines for U.S. Thanks to "Dirty" Fuel
Lean-Burn tech has been around for quite some time - Honda's had VX and HX civics since the early 90s - but stopped using them in 05/06 (Civic and Insight hybrids). Nissan and Toyota have also had their own variants... but they too have gone out of production.
The systems all have cut-off points for load and RPM - lean burn only works on a very narrow band of conditions. Even then, the trade-offs are noticed - the engines are more expensive, the O2 sensors cost a fortune, and warranty costs were substantially higher and were all very difficult to troubleshoot.
With today's more sophisticated controls systems, the hardware is simpler and easier to manage. As the next generation of economy engines comes around (HCCI over current DI) we'll see lean burn come back into the fold.
FWIW a 2000 Civic was rated 32/37mpg (now 27/33) and a Civic HX was rated 35/43mpg (now 30/39).
I'm guessing (at the time) the warranty costs and upfront costs to manufacture and price to consumers could not justify the mpg increase - which lead to their decline and disuse.
And I'm guessing if Mercedes *really* wanted to, they'd have the car here and are just making excused. Honda, Nissan, and Toyota were able to do it 15 years ago. And Chrysler had a lean-burn carburetor system nearly 30 years ago!
The systems all have cut-off points for load and RPM - lean burn only works on a very narrow band of conditions. Even then, the trade-offs are noticed - the engines are more expensive, the O2 sensors cost a fortune, and warranty costs were substantially higher and were all very difficult to troubleshoot.
With today's more sophisticated controls systems, the hardware is simpler and easier to manage. As the next generation of economy engines comes around (HCCI over current DI) we'll see lean burn come back into the fold.
FWIW a 2000 Civic was rated 32/37mpg (now 27/33) and a Civic HX was rated 35/43mpg (now 30/39).
I'm guessing (at the time) the warranty costs and upfront costs to manufacture and price to consumers could not justify the mpg increase - which lead to their decline and disuse.
And I'm guessing if Mercedes *really* wanted to, they'd have the car here and are just making excused. Honda, Nissan, and Toyota were able to do it 15 years ago. And Chrysler had a lean-burn carburetor system nearly 30 years ago!
Engine out NOx for a lean burn engine is not high, but when the normal catalyst doesn't work, post-catalyst NOx is high, compared to a stoichiometric car.
Our gasoline has more sulfur, because the oil we have access to has more sulfur. It would take more refining to get rid of it than it does for Europe.
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