Written by Joel Paynton Thursday, 08 April 2010 09:15
Volume 3 Issue 1 - Diesel Articles
Fuel Economy, Coming Right Up!
The main feature that I am excited about in the new 2011 Chevrolet Silverado HD Duramax LML is not the exhaust brake, not the trailer sway control or hill start assist, not the new body style, or even the USB connectivity, mobile WiFi or Bluetooth. Don't get me wrong, those are all great features. What is truly going to make this truck far more usable than the LMM generation is the selective catalyst reduction (SCR) system. Now this does add complexity to the exhaust system with another series of emissions components. And yes, the extra complexity can create more possibilities for failure. In general, we can always expect some teething problems when a newly designed vehicle is initially produced. But the SCR system buys for us one critical feature: fuel economy.
2011 Duramax LML diesel engine with new Allison 1000 transmission
Actually, the SCR system provides a potential cascade of benefits which improves driveablility and convenience as well as fuel economy. The SCR emission system utilizes an additional catalytic converter located behind the diesel particulate filter. When a reductant is injected into this catalytic converter (the reductant in this case is a urea-based solution known as diesel exhaust fluid) it allows oxides of nitrogen to be converted and broken down into harmless nitrogen and water. This is the main reason the new 2011 LML Duramax reduces NOx emissions by 63%.
Jim Minneker, Assistant Chief Engineer for Duramax Diesel, introduces the 2011 Duramax Diesel
Traditionally, NOx emissions were controlled by heavy use of the EGR valve. This has several drawbacks, including soot buildup in the intake duct system. The additional soot does not bode well for the diesel particulate filter (DPF) either and the use of the EGR valve plugs the diesel particulate filter more frequently, increasing the frequency of regeneration cycles. Basically, the more soot the EGR produces the faster it wills clog the DPF. As we all know, regenerating a diesel particulate filter consumes diesel fuel and so reduces fuel economy. By adding the SCR system, use of the EGR valve can be greatly reduced. This translates into several benefits, including reducing the need for regeneration cycles, which, of course, improves fuel economy and extends the life of the diesel particulate filter. It also has a side benefit of reducing soot build up that normally occurs in the intake manifolds of an EGR-equipped diesel.
Many of us who owned the LMM diesel have been greatly annoyed by the clean exhaust filter message. Once the message appears, the driver is obligated to take the truck and drive it faster than 50 mph for an extended period of time in order for the ECM to complete a regeneration cycle. At times, the diesel particulate filter can become so clogged that the ECM sets a trouble code and operates in limp mode. Any improvement here will be certainly welcome (at least by the owners of the new trucks) and GM is claiming that there is a 75% extension between regeneration cycles.
The SCR system is not the only reason for the improved NOx emissions. There is also a redesigned fuel system which includes fuel injectors that can operate up to 30,000 PSI. These are piezo-actuated fuel injectors which are faster and more precise than previous generations. Improved fuel injection strategies can reduce peak combustion pressures and temperatures that form NOx. Improved fuel injection control also translates into quieter engine operation.
Bringing this back down to the bottom line, these improvements all contribute to improved fuel economy and reduced driver inconvenience. That in itself is worth the added exhaust system components and the diesel exhaust fluid reservoir.
Stopping the Beast
A second very welcome feature is a larger brakes. In my opinion, the brakes on the previous generation GMT 800 and GMT 900 trucks have left much to be desired. It is not uncommon to see heat stressing and surface cracking on the front rotors of a heavy-duty Chevrolet Silverado or GMC Sierra. Improving the brake system has been long overdue.
Several changes have been made to the breaks including larger rotors, a re-calibrated hydroboost and redesigned calipers. The braking feel will be more positive because the brakes will be able to handle longer braking cycles and reject heat better.
The exhaust brake system will also help preserve the life of the brakes and help prevent brake rotor overheating with large loads. This, however, is not an entirely new system. The exhaust brake feature has been available on medium duty trucks since 2006. It is simply an additional software routine in the ECM that allows the turbo vanes to close completely under certain breaking conditions, creating additional exhaust back pressure which helps to hold the vehicle and load back. There is no additional exhaust brake that is physically installed in the exhaust system. It is simply a modification of the way the existing turbocharger vane system is used. It surprises me that this feature has not been included with Duramax trucks since 2006. It is a long overdue but welcome feature.
Crazy Towing Payload
In what seems to be a race to haul the biggest load, GM has again leapfroged the competition. I don't know of anyone who owns a 20,000-pound fifth-wheel trailer. I do know some people who terribly overload trailers, but that does not count. Still, we can be assured that improving the payload capacity translates into a number of other areas in the truck: the cooling system, axles, bearings, transmission, transfer case, front and rear differential, suspension system, frame and even the fuel capacity. All of these areas have to be addressed and improved in order to handle the much higher payloads the new Duramax is capable of.
A first for the HD line of trucks: GM is offering a Denali package
Little Things
There are a number of little things that I'm excited about in the 2011 Duramax.
- The availability of 20-inch wheels. Finally!
- A larger fuel tank. Finally!
It seems that General Motors is actually listening or at least paying attention to what their customers are doing to their trucks after they purchase them. First thing I do with a truck when I get one is to make modifications to it so that it can handle real-world work applications better. Combined, these little modifications make the truck much better, in my opinion, than when it rolled off the factory line. My own truck features greatly improved handling due to careful choice of steering modifications, wheels and tires. Frankly, I wouldn't have it any other way and I intend to continue modifying my truck with a larger fuel tank, better entertainment system and further enhancements to the suspension and brakes to make my truck more, well, mine. Likewise, it is the sum of all the little enhancements, combined with a few big ones, that make the new 2011 Chevrolet Silverado a far more capable truck. It would seem that the General is reading my mind. When I consider all of the new refinements included on the 2011 Duramax-powered trucks, I am much more likely to actually buy one.
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Chris Novosad
said:
 |
czech tech the General needs to take notes from Czech truck maker Tatra they build diesels that meet Euro 5 emmissions with NO E.G.R. PARTICULATE FILTEWR AND THEY STILL USE MECHANICAL INJECTION NOT COMMON RAIL IMAGINE IF THEY USED A BOSCH PIZO SYSTEM THE TATRA DIESEL IS ALSO LABLED AS A NEAR ZERO EMMISSIONS DIESEL |
Ernie McFerrin
said:
 |
N/A All the new enhancments sound great. I do not understand why GM does not offer an auxilliary fuel tank option. I added an extra tank to the bed of my 2003 Dually and can now put about 75 Gallons on board which allows me to generally have sufficient fuel to do a round trip run on the initial fill up. This cost me about $750.00 and I would be happy to pay for a factory install under the bed. 36 gallons does not cut it for a long all day drive and I do not enjoy dealing with getting in with my 36 foot trailer to fill up. Do not even get me started with trying to fill up at a truck stop. No Way! Listen up GM, this is overdue and should be offered as an upgrade to new buyers. |
Mike Moorehead
said:
 |
... I own a 2011 Chevy crewcab dually and anytime I drive in the north where the temp is below freezing, the def tank and lines freeze also causing the speed limiter to kick in. I then have to stop at a dealer to have the system reset. This has happened 4 times in 6 months and I use this vehicle for my business |
BEAU BELL
said:
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... MIKE MOOREHEAD, YOU NEED TO TAKE YOUR TRUCK INTO THE DEALER AND HAVE THEM RUN THE RECALL THAT IS ON THAT TRUCK PERTAINING TO THE DPF FILTER, ALSO THAT TANK WILL HOLD UP TO 7 GALLONS BUT YOU NEED TO ONLY FILL IT UNTILL IT BURPS WHICH IS ABOUT 5 GALLONS. IT NEEDS THE EXTRA ROOM TO EXPAND AND CONTRACT |
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