29 September 2012
The ASME Internal Combustion Engine Division 2012 Fall Technical Conference was held September 23 - 26, 2012 at the Sheraton Wall Centre Hotel in Vancouver, British Columbia. The meeting, hosted by Westport Innovations, had a significant natural gas focus. There were about 200 registered attendees and the two-day technical program included 98 technical papers. On the third day, participants could attend a tour of the Vancouver facilities of Westport Innovations.
Keynote Lectures. The conference started with a keynote address by Dr. Patric Ouellette (Vice President and Chief Technology Officer, Westport Innovations) on Technology Choices for Up and Coming New Applications of Natural Gas as an Engine Fuel. While fuel cost savings is an important driver for adopting natural gas across all categories ranging from passenger car applications to marine vessel propulsion engines, other factors come into play in each category as well.
Natural gas fueled passenger car and light-duty vehicles are almost all based on spark ignition (SI) gasoline engines that have been adapted for bi-fuel operation and fuel storage is primarily CNG. Light trucks and other work vehicles are the most common natural gas vehicles in North America in this category. Stricter CO2 and fuel economy regulations are important drivers for technology development with downsizing and on-board fuel storage presenting significant challenges.
Medium-duty and medium heavy-duty applications are typically based on diesel engines that have been converted to natural gas. Fuel storage can be either CNG or LNG. Refuse trucks are an important class of vehicles adopting natural gas in this category. Engine strategies include electronically controlled SI lean burn and stoichiometric SI engines with a three-way catalyst such as that used by Cummins Westport. Important differences between this segment and the light- duty segment include: higher engine loads, the relative importance of high load engine efficiency, reliability and durability expectations, higher firing pressures and limitations on piston shape and in- cylinder air motion. Natural gas’s lower carbon intensity and its potential to facilitate meeting the upcoming EPA limits on CO2 emissions from heavy-duty engines is an important driver for this category.
Heavy-heavy-duty on-road vehicles applications are also primarily based on diesel engines adapted for natural gas. Technology options include direct-injection (such as Westport’s HPDI), dual fuel options that use a diesel injection to ignite a premixed natural gas/air mixture, lean SI and stoichiometric SI with a three-way catalyst. On- board fuel storage is either CNG or LNG. For some of these approaches, methane emissions can pose a significant challenge. Other factors that must be considered here include the compatibility of vehicle aerodynamic features, such as fairings, with the fuel storage system and the effect of new engine technologies such as advanced combustion, exhaust waste heat recovery and no-idle strategies. Technology drives are similar to those for medium-heavy-duty. In DI applications where the natural gas burns in a diffusion flame, up to 80% of combustion generated soot can originate from the natural gas at high loads and a diesel particulate filter and SCR catalyst is still required for US EPA 2010 applications. However, DI does offer higher torque than the premixed options making it preferable for long-haul trucking applications.
Locomotive Engines. While the conference has evolved to cover all sizes and applications of internal combustion engines, large bore engines have traditionally received a lot of attention. This year, several large bore engine papers focused on emission control, a trend driven in part by the approaching US EPA Tier 4 (2015) locomotive emission standards, locomotive upgrade requirementsunder the voluntary agreements between railways and the California ARB and other local programs.
Paul Park of Caterpillar [Paper No. ICEF2012-92198] discussed SCR- based aftertreatment system designed for repowered locomotives to meet California low NOx targets. Five 2,240 kW (3,005 hp) PR30C line-haul Progress Rail locomotives equipped with the aftertreatment system have been operated in revenue service by Union Pacific. The aftertreatment module included 4 DOC catalysts (2x2), followed by urea injection and mixing and 16 SCR catalysts (4x4). All catalysts used metallic Emitec substrates, either round (606 mm diameter x 90 mm) or square (606x606x90 mm) with rounded corners, with 100 cpsi cell density. Resonance frequency analysis was used during the design process to ensure mechanical durability. Catalyst coating was supplied by BASF. The technical challenges included high percentage of idle in real operation and high SOF fraction of the PM emissions, especially at lower notches (98% SOF at idle, 72% at notch 1). Dual DOC technology was used: a front DOC with high Pt on alumina, to provide protection from HC and the NO2 function, followed by a DOC with low Pt with Ce on alumina for SOF control. Vanadia-based technology was used for the SCR catalysts. The system included a 1,000 liter urea tank. High NOx conversions were achieved (87-90% above 340 C, 81-83% over the line haul cycle) with very low ammonia slip, even though the system did not include an ammonia slip catalyst. The control system utilized NOx sensors upstream and downstream of the catalyst module. The system controlled NOx, HC and CO emissions to below Tier 4 levels. PM emission reductions were 38-58%. Hence, with minor development, the system has potential for meeting Tier 4 standards in new locomotives.
One of the Progress Rail locomotives with the DOC+SCR system was evaluated at the Southwest Research Institute (SwRI) . The evaluation involved a field trial with data logging equipment installed and laboratory emission testing at 0, 1,500 and 3,000 hours. Cycle composite HC, CO, and NOx remained below Tier 4 limits, and PM remained at approximately half of Tier 3 limits. Emissions remained stable, with the results from the 1,500-hour and 3,000-hour conditions similar to the 0-hour condition. NOx reductions during the field operation depended on the route and the percentage of idle, light- and heavy load operation. On average, NOx was reduced by 54% during the field trial. In total, the five PR30C-LE locomotives equipped with the aftertreatment system completed a cumulative 30,800 hours of revenue service through June 2012 without report of a major issue.
Combustion. Traditionally, the conference program included a number of fine papers on combustion topics. ETH Zürich presented a fundamental study of the effect of post injections on diesel soot emissions using multi-color pyrometry . Among other things, they found that the time phasing of soot evolution has a significant impact on the optimal post injection dwell time. Soot reduction potential with post injection decreases rapidly when it is timed late in the soot oxidation phase. Soot oxidation can only be improved by induced turbulence from the post injection when it occurs near the in-cylinder soot peak.
Clemson University and the University of Michigan carried out cycle-to- cycle air fuel ratio calculations during transient engine operation using fast response CO and CO2 analyzers . For the engine tested (SI engine with low dilution), they found a maximum difference of approximately 10% compared to more conventional methods. The difference was expected to be higher with more charge dilution.
Other Topics. A team of researchers from AVL and partners reported on an investigation of the limits for NOx reduction using EGR . Nonroad engines were the focus of the study, but a modified Euro V engine was used in the experiments. With the used test engine, NOx emissions could not be lowered below 0.6 g/kWh over the NRTC test without a significant deterioration in load response. Thus, EGR alone was not sufficient to meet the nonroad Stage IV limit of 0.4 g/kWh. The high EGR rates required very high cooling power—approximately 43% of the brake engine power, compared to about 22% in typical Euro V applications.
Using their mobile chassis dynamometer facility, the West Virginia University evaluated drayage truck test cycles  that were developed by TIAX and commissioned by the Long Beach and Los Angeles port authorities. The tested vehicle was a 2011 Class 8 Mack truck with DOC, DPF and SCR aftertreatment. Drayage cycles were run using two approaches: (1) as a series of shorter tests (called drayage activities) and (2) as a single continuous drayage operation cycle. Emissions calculated from integrated drayage activities were significantly higher than those measured over single continuous drayage operation, approximately 14% to 28% for distance-specific NOx emissions. This was likely explained by differences in the state of the SCR system (temperatures, adsorbed NH3). Relatively high NOx emissions were measured at some low- to medium-load segments, probably due to urea injection being shut off at the particular conditions due to insufficient temperatures.
CANMET researchers tested retrofit urea-SCR systems on underground mining vehicles . The project was conducted at the Sifto salt mine in Goderich, Ontario. Salt mines often have problems with NO2 exposures due to the large volumes and slow ventilation rates in salt mining. In the case of the Godrich mine, with production areas located underneath the bottom of Lake Huron, the problems are even more severe as ventilation air must be pumped over long distances under the lake. Two SCR systems were installed: one on a Cat 990G loader (SCR system by Tenneco) and one on a Cat 775D truck (Nett Technologies). Both systems provided similar NOx reduction efficiencies: 60-65% over the vehicle duty cycle and a peak reduction of about 80%. The Nett SCR package proved to be more robust and had fewer technical issues—after the trial, the mine ordered several Nett systems. The SCR technology had good acceptance at the mine.
Conference website: asmeconferences.org/ICEF2012