27 October 2012
The 18th DEER (Directions in Engine-Efficiency and Emissions Research) Conference was held this year on October 15-19 in Dearborn, MI. The focus of the conference—organized by the US Department of Energy (DOE)—was on engine efficiency, including both diesel and gasoline powertrains. The conference included about 80 presentations and about 85 posters, as well as an exhibition. With about 700 registered participants, conference attendance was down from previous years. Other notable differences to past conferences included: a full-conference registration fee of $495 for all conference attendees as a result of “new federal agency regulations” and the absence of corporate sponsors.
Technology & Regulatory Trends. The stage for the conference was set by a plenary session “A View from the Bridge”, devoted to trends in fuels and technology for both light- and heavy-duty vehicles. Engine development trends were also the subject of a panel discussion, “The Next ICE Age” that opened the second day. Hydrocarbon fuels will remain indispensable to fulfill growing energy demand. Renewables will be important to meet some of the increased demand but will unlikely be able to fill the entire gap. Most of the demand growth is expected in non-OECD countries while demand in OECD countries is expected to remain flat. Natural gas, crude and coal will meet most of the demand for the foreseeable future while biofuels and other sources will play a smaller but still important role. Current vehicle support infrastructure has a life of about 50 years while vehicle life is about 10 years. Because of these life expectancy differences, addressing future mobility challenges in the next few decades will fall on changes to vehicles while their maintaining ability to use the existing infrastructure. LNG is attractive in North America where it’s landed price is in the neighborhood of $3/MMBtu. In the EU, the landed price is over 3 times higher around $10 while in Asia it’s in the $13-15 range. Developments in “Small scale” LNG facilities are important for mobile applications such as marine [W. Warnecke, Shell].
The cost differential between natural gas and diesel is expected to persist. By 2050, 40% of heavy-duty Volvo trucks are expected to be natural gas fueled. However, diesel fuel will still account for 77% of the fuel used by heavy-duty vehicles—the difference presumably relates to the different applications for which the infrastructure around the two fuels will likely develop. It is unlikely that the “conventional” diesel engine cycle will achieve efficiencies beyond about 50%. Higher efficiencies will require “different thermodynamic cycles”. Expected engine BSFCs for 2018 are 0.29 lb/bhp-hr (176 g/kWh) and for 2050 are 0.26 lb/bhp-hr (158 g/kWh). If California proceeds with the recently discussed heavy-duty NOx limit of 0.05 g/bhp-hr, fuel economy gains may be harder to achieve [A. Greszler, Volvo].
Engine downspeeding can provide 1.5-3% fuel economy improvement per 100 rpm. Current heavy-duty engines operate at about 1400 rpm at highway cruise conditions. Future cruise targets of 900 rpm are considered possible. To get there, automated manual transmissions (AMTs) would be required as manual transmissions can become too difficult to drive. Current drivelines limit downspeeding of highway cruise to about 800 rpm while current engines limit it to about 700 rpm. Supercharging and its ability to boost low engine torque and improve throttle response could also deliver fuel economy benefits that range from about 2.3% for highway trucks to 22% for some vocational applications. While hybrid drivelines have already seen use in heavy-duty applications, they have been almost entirely supported by incentives. In order to be viable, hybridization must be “affordable” and provide a payback in 3 years or less via fuel savings [T. Stover, Eaton].
SuperTruck Program. Heavy-duty engine and vehicle manufacturers talked about progress on their SuperTruck engines and vehicles. The SuperTruck program, sponsored by the US DOE, includes several goals: (1) a 50% increase in vehicle freight efficiency measured in ton-miles per gallon, (2) at least 20% of this improvement should be achieved through engine efficiency developments and the engine should achieve 50% engine brake thermal efficiency (BTE) under highway cruise conditions and (3) evaluate potential approaches for a 55% BTE engine. However, there are some differences in the objectives of the various participants—perhaps reflecting differences in the details of individual proposals. For example, Cummins has an additional objective to demonstrate a 68% freight efficiency improvement over a defined 24 hour duty cycle that includes an extended idle and is representative of line haul applications. Most participants focused their presentations on the first two objectives and with one exception noted below, approaches to meeting the 55% BTE objective remain unclear at this time.
Elements of some of the approaches developed during the Supertruck program may eventually see commercial application for meeting EPA heavy-duty GHG regulations after 2017. Some view the 2017 limits (e.g., 460 g/bhp-hr CO2 and 4.52 gallons/100 bhp-hr fuel for engines in on-highway tractors) as technology forcing.
Cummins Supertruck platform is based on their 15 L ISX engine. They have demonstrated the highest BTE efficiency to date, 49.3%. The 50% target is expected to be achieved via further optimization. Engine design changes to reach this efficiency included: a compression ratio increase, piston bowl shape modifications, injector specification and calibration optimization. Gas flow optimization improvements included: lower pressure drop EGR loop and improved turbocharger matching. Parasitic losses were addressed with a lower friction cylinder kit, lowering cooling pump power requirements and by using waste heat recovery (WHR). The WHR system is based on an Organic Rankine Cycle (ORC) and included an EGR boiler/superheater, an exhaust boiler (located after the aftertreatment system (ATS)) and a recuperator. Power output from the WHR system is fed via a mechanical transmission to the engine output shaft. The 50% freight efficiency improvement will rely on aerodynamic improvements, the 50% BTE engine, transmission/axle optimization, tire rolling resistance reductions, route management and vehicle weight reductions and is expected to be demonstrated in December 2012. A 65% freight efficiency improvement will rely on further aerodynamic improvements, a further increase in engine efficiency and the use of engine idle management and is expected to be demonstrated in December 2013 [D. Koeberlein, Cummins].
Aftertreatment Technologies. An update on the Amminex gaseous ammonia delivery system was presented by Tue Johannessen of Amminex. While the relationship with Faurecia has been ongoing, they have also been working with Tenneco to explore the potential for gaseous ammonia in North America. It was noted that the value of the system is that gaseous ammonia can be introduced in the exhaust system at lower exhaust temperatures than urea can be injected. This can provide a significant cold start NOx emissions benefit. In heavy-duty applications where cold start emissions are less of an issue, a case for gaseous ammonia is harder to make [T. Johannessen, Amminex].
A number of videos illustrating the movement of ash within the individual channels of a DPF were shown by MIT. Engine out ash particles are very small and usually dispersed within the individual engine-out PM particles. PM (and thus ash) is deposited relatively uniformly over the DPF channel surfaces. As the carbon fraction is oxidized, the ash particles are left behind and tend to agglomerate together into “sheet-like” deposits. These are then transported to the end of the channel where they agglomerate further to form an ash cake with significant void volumes [A. Sappok, MIT].
Challenges of integrating an SCR catalyst into a DPF were discussed by Haldor Topsoe. The SCR catalyst must be able to survive the temperatures experienced during active regeneration—about 800-900°C. Common copper and iron zeolites as well as vanadium pentoxide based SCR catalysts are not stable at these temperatures and may not be suitable if DPF temperatures exceed the above values. However, copper chabazite and similar materials are stable and even require high temperatures to become fully activated. An integrated DPF/SCR catalyst with such an SCR catalyst applied to the outlet side of the DPF was tested on a Euro 5 light-duty engine. It was noted that ammonia emissions control requires an ammonia slip catalyst and the presence of urea on the DPF caused some reduction in passive regeneration [K. Johansen, Haldor-Topsoe].