Fleet Management News & Business Info | Commercial Carrier Journal
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EQUIPMENT: 13L vs 15L ENGINES will debut in January,��� he says. ���Our broad horsepower range works for most customers.��� Navistar saw the trend toward 13-liter power coming some years ago as customers became more focused on weight, payload and fuel ef���ciency, said Steve Gilligan, vice president of vocational and product marketing. ���That���s what drove us in our development of our MaxxForce 13,��� Gilligan said. ���The added weight of emissions-related equipment and ���uid is offset by the 13-liter engine.��� Jennifer Rumsey, executive director of heavy-duty engineering for Cummins, notes that most of today���s 13-liter engines actually are 12- to 13-liter engines. While engines in this class have displacements ranging from 11.9 to 13 liters, 13-liter and 15-liter displacements ���ll different needs within the Class 8 truck market, she says. The Cummins ISX12 ��� which shares common components with the ISX15 ��� has been optimized for regional hauling and less-thantruckload operations, as well as vocational applications such as dumps and mixer trucks and ���re and emergency vehicles. ���The older thinking was to buy a larger engine and run it easy ��� it���ll get good fuel ef���ciency and last forever,��� says David McKenna, powertrain sales and marketing manager for Mack Trucks. ���There is a perception that bigger is better for a long-life engine ��� I strongly disagree. Our 13-liter Mack MP8 engines have accumulated a phenomenal amount of miles. During disassembly and inspection, we were more than pleased with our design criteria being met easily based upon million-mile wear observations.��� Going even smaller, Mack now has customers using its 11-liter MP7 who are seeing a documented 2 percent fuel ef���ciency improvement compared with a 13-liter and 3 percent compared with a 15-liter, McKenna says. ���Correct engine sizing is the base from which to optimize performance,��� he says. ���If you start from the wrong base, nothing else you do will be correct, and maximum optimization will never be achieved.��� Ed Saxman, drivetrain product manager for Volvo Trucks, says Volvo had a 12-liter engine that it increased to 13 liters due to power density so that the top rating could be increased to a full 500 horsepower with 1750 lb.-ft. of torque. ���We also introduced our 11- and 16-liter engines to be able to offer additional lighter-weight and higher power options,��� he says. Gilligan contends that the market shift isn���t de���ned wholly by displacement for displacement���s sake. ���What you���re seeing more in more, in terms of engine technology, is a smaller-displacement, lighter-weight and more ef���cient engine delivering the same level of horsepower that was only achieved in the past with a 15-liter engine,��� he says. ���Average horsepower has shifted only slightly over the past 10 years. The same ���eets that were running 430-horsepower Correct engine sizing is the base from which to optimize performance.��� ��� David McKenna, powertrain sales and marketing manager, Mack Trucks engines a few years ago may have shifted peak horsepower upward, but torque is relatively unchanged and is well within the ef���cient operating range of 13-liter engines.��� Larger-displacement engines can offer higher torque without adversely increasing peak cylinder pressure, Saxman says. ���Horsepower and displacement are less connected than many think,��� he says. In Volvo���s case, the average delivered horsepower of the 13-liter engine in its tractors has been slightly higher than the average horsepower of the 15-liter supplier engine that it delivers. ���The same was true for our 12-liter, which preceded the 13-liter.��� Volvo uses similar designs for both displacements, and the design concept can be used across three displacements, but some part sizes may vary out of necessity. ���While one might surmise that a larger displacement means more robust part design, that is not necessarily true,��� Saxman says. ���The Volvo D13 connecting rod is more robust than those of other larger-displacement engines.��� McKenna believes Mack���s MP7 at the 32-horsepowerper-liter power density has proven to be the right balance DAIMLER���S FREIGHTLINER AND WESTERN STAR BRANDS SUPPLY 13-, 15- AND 16-LITER DIESEL ENGINES, INCLUDING THE DD13, FROM ITS INHOUSE DETROIT LINEUP. for engine fuel economy and performance versus power output. ���Potentially, the largerdisplacement engines should see the power density number increase, as the larger mass platform can offer greater strength in the block and crank areas,��� he says. If an acceptable power density from each engine is maintained, the smallerdisplacement engine should get better fuel economy since it has lower internal friction, less reciprocating mass and a lower weight. ���Reducing tare weight alone contributes to better TWELVE POWER RATINGS ARE AVAILABLE FOR VOLVO���S 13-LITER D13 ENGINE IN THE RANGE FROM 375 TO 500 HP. COMMERCIAL CARRIER JOURNAL | JANUARY 2013 41