Conference report: ASME 2015 ICE Fall Technical Conference

26 November 2015

The ASME Internal Combustion Engine Division 2015 Fall Technical Conference (ICEF 2015) was held November 8-11, 2015 in Houston, Texas, USA. The conference—attended by over 200 delegates and hosted by OneSubsea—included a two-day technical program with about 95 technical papers. On the third day, participants could take part in a technical tour of the GE Oil & Gas Port Northwest facility, the global headquarters for GE’s Reciprocating Compression business and the main manufacturing facility for Copper-Bessemer and Ajax gas engines and Superior separable compressors. It was the first Internal Combustion Engine conference conducted under the new “One ASME” formula, with conference administration and logistics support provided by the ASME headquarters, rather than ICE Division volunteers as was the case in the past.

Keynote Lecture. The conference opened with a keynote presentation by Mark Patterson of GE Oil & Gas who gave an overview of GEs natural gas compression engine technology. GE acquired their gas compression engine line from Cameron in 2014. GE produces engines used in a variety of natural gas extraction and transmission functions ranging from well head compression to pipeline compressor stations. Primarily these engines are 2-stroke SI engines that share a common crankshaft with the compressor. Other features that these engines share in common are lean burn combustion, direct fuel injection and port scavenging.

At the small end of the GE gas compression engine line is the Ajax. This engine first dates from the 1960s is currently produced with 1 to 4 cylinders and power ratings from 193-800 hp. It is primarily used for wellhead compression. The latest version of the engine is naturally aspirated and has a 7:1 compression ratio. To ensure adequate scavenging of burned gas from the cylinder, a 43 ft long expansion chamber is used in the exhaust line. Engine efficiency at full load is 7500 BTU/bhp-hr (about 34% BTE).

At the large end of the spectrum is the Cooper Bessemer W-330 pipeline compression engine. This engine with an 18” (457 mm) bore and 20” (508 mm) stroke is available with up to 16 cylinders and in power ratings up to 8000 hp. It is turbocharged and has a compression ratio of 9:1. Engine efficiency is reported at 6300 BTU/bhp-hr (40% BTE). Interestingly, GE does not currently produce block castings for these engines, All new engines are produced using re-claimed cylinder blocks.

Under US law, gas compression engines are considered stationary sources of pollution and are therefore subject to a complex system of federal, state and/or local regulations and permit policies. NOx emission standards for these engines can vary widely depending on where they are located. However, the strictest limits on NOx for these engines are 0.5 g/bhp-hr such as those imposed in the Houston-Galveston-Brazoria area and the engines are designed to be capable of meeting these limits. To meet a 0.5 g/bhp-hr NOx limit, GEs engines from the Ajax to the Cooper Bessemer W-330 use a lean burn strategy and a center mounted pre combustion chamber to control NOx in-cylinder. The engines also use an oxidation catalyst to limit CO. Because gas quality can be unpredictable, compression ratio has to be limited.

Tuesday’s lunch time industry talk was given by Charles Roberts, Director of Diesel Engines and Emissions R&D at Southwest Research Institute. As suggested by the title “Has the Playing Field Changed again for Future Diesels”, the talk focused on how upcoming changes to the regulatory framework will affect the diesel engine industry.

Greenhouse gas regulations for heavy-duty on-road engines will ask for a further 5% reduction in GHGs in the 2017-2027 timeframe. Certifying vehicles using these engines is a challenge because any particular engine model can be used in a wide range of vehicles with numerous drivetrain component combinations. The current approach for many vehicles is to certify the engine and then the vehicle using EPAs GEM simulation tool. Hardware in the loop (HIL) tools that simulate vehicle parameters with a computer model and couple them to a dynamometer mounted engine are another option that has been incorporated into the regulations. Testing at SwRI has shown that there is less than a 5% difference in GHG emissions between HIL simulations and chassis tests.

California’s low NOx program that is targeting 0.02 g/bhp-hr NOx for heavy-duty trucks will see significant changes in theses vehicles. Reducing cold start NOx emissions would be critical to achieving such a level of NOx emissions. For a diesel engine calibrated for relatively high engine out NOx (~3+ g/bhp-hr) to minimize GHG emissions, a cold start SCR conversion efficiency of 96% and a hot start efficiency of 99.5% would be required. Changes to the federal ozone standard provides additional impetus for a US federal NOx limit of 0.02 g/bhp-hr.

SwRI has organized a number of Clean High Efficiency Diesel Engine consortium for 24 years with the 7^th phase launched last month. One of the goals of the last phase of the CHEDE program was to achieve an engine BTE of about 48% before the addition of waste heat recovery (WHR) and to raise this to 55% using WHR. A 49% BTE has already been demonstrated in a 15 L engine. Potential topics for the next phase include managing heat loss in a way that will allow them to be exploited for waste heat recovery (e.g., insulated piston crowns and combustion chamber designs that keep the flame away from the piston wall); reducing friction and parasitic losses through such measures as engine bearing design and material selection, reducing cam lobe pressure, piston coatings for reduced friction, reducing lube oil flow requirements and pump optimization. The potential for pulse turbocharging to improve turbocharger efficiency will also be an important topic for consideration.

Gas Engines. The methane number (MN) index was developed to characterize the propensity of gaseous fuels to “knock” in spark ignited engines. Dual fuel engines where natural gas is premixed with air and ignited by a diesel pilot are being developed for a range of applications including North American locomotives. The ability of MN to predict rapid combustion in dual fuel engines was examined by Caterpillar and Southwest Research Institute [ICEF2015-1119]. This study used the MWN algorithm to estimate MN. In this study, a range of fuels with MN between 70 and 100 were blended using methane, propane and butane and tested in a dual fuel engine at SwRI. What the study found was that dual fuel combustion is sufficiently different from spark ignited combustion that MN may not capture all of the phenomena that influence rapid combustion behavior of premixed fuels in dual fuel combustion systems. For example, at a MN 80, the transition to rapid combustion occurred between a lambda of 1.95 and a value greater than 3.3 depending on whether propane, butane or both were added to methane to achieve the 80 MN. If MN was a good predictor of the transition to rapid combustion in dual fuel combustion systems, the range of lambda’s over which the transition occurred would be expected to be much narrower.

In order to better understand the knocking characteristics of gaseous fuels in spark ignition engines, researchers from Osaka Gas, Osaka Institute of Technology and Kyoto University examined the knocking behaviour of various pure gases (CH₄, H₂, C₂H₆, C₃H₈, n-C₄H₁₀ and i-C₄H₁₀) and dual component blends of these gases with methane [ICEF2015-1079]. For the pure fuels, hydrogen is the most prone to knock. When ignition properties are considered, hydrogen has an higher auto ignition temperature (when compared at similar temperatures) and longer ignition delay than most of these fuels and the reason for its extreme sensitivity to knock is not readily apparent. Upon closer examination, hydrogen has a higher ratio of specific heats that causes the unburned fuel and air mixture temperature to be considerably higher at the end of the compression stroke (more than 100K in some cases). Since ignition delay is an exponential function of temperature, the actual ignition delay with hydrogen under engine conditions can thus be about an order of magnitude shorter than for the other fuels. Additionally, the unburned gas temperature with H2 is increased easily during the combustion phase because of its high burning velocity that promotes compression by the flame front.

A team from the University of Wisconsin-Madison compared two dual-fuel (natural gas and diesel) combustion strategies: reactivity controlled compression ignition (RCCI) and diesel pilot injection (DPI) [ICEF2015-1128]. The experiments were conducted in a 2.44 L Caterpillar 3401E Single-Cylinder Oil-Test Engine (SCOTE). The transition between the combustion regimes was achieved through a change in injection timing, with SOI at -38.1° aTDC for RCCI (early injection) and SOI at -14.1° aTDC for DPI (late injection). At rich conditions (φ=0.72) both combustion modes had similar performance. At lean conditions (φ=0.5), RCCI had higher efficiency and lower emissions than DPI. At lean conditions, RCCI had about 8% higher indicated thermal efficiency than DPI; most of this (~5%) was due to lower combustion losses, as well as to lower coolant heat loss (~2%) and lower exhaust heat loss (~1%).

Another study to investigate the combustion and emissions of a natural gas - diesel dual fuel engine was conducted by NRC Canada [ICEF2015-1041]. A single cylinder version of the Caterpillar 3400 series diesel engine was modified to operate as a dual fuel engine, with natural gas injected into the intake port.The experiments were conducted at low and medium loads, with natural gas substitution rates increasing up to 50 and 70%, respectively. It was found that natural gas substitution retarded combustion phasing because of the higher ignition temperature of natural gas. The dual fuel combustion slightly decreased brake thermal efficiency, significantly reduced CO₂, and increased methane emissions. The total CO₂ equivalent GHG emissions were either decreased or increased, depending on engine operating conditions. PM emissions were significantly reduced, while NOx emissions increased in the dual fuel mode compared to diesel operation.

Locomotive Engines. ABB presented the results of a comprehensive simulation study that analyzed a number of turbocharger and EGR strategies for a US Tier 4 rail engine [S. Bernasconi, ICEF2015-1076]. The engine was equipped with a two-stage turbocharger that could provide a pressure ratio of about 11 and a wider range of volumetric flow than a single stage turbo. Three control options were compared: (1) system turbine wastegate, (2) HP turbine bypass with LP turbine VTG, and (3) stepless variable valve timing (VVT). The engine was equipped with a high-pressure EGR system based on the donor cylinder concept, where some of the engine cylinders are used to pump exhaust gas to the intake receiver. For an EGR rate of 30%, this required 4 out of 12 cylinders. A valve was used to bleed off excess EGR gas to the exhaust receiver.

The VVT configuration offered the lowest fuel consumption at high engine load. In most cases, it also enabled lower cylinder temperature. The drawbacks included a limited flexibility to control the turbocharger speed and the operating points in the compressor maps.

In its second part, the study assessed five exhaust gas recirculation strategies: (1) EGR driven by 4 donor cylinders (in a 12 cylinder engine), (2) EGR driven by an electrical blower, (3) EGR driven by a turbocharger, (4) semi-short routing, with the EGR stream introduced between the LP and HP compressors, (5) semi-short routing with 3 donor cylinders. The last configuration—semi-short routing with donor cylinders (shown in the schematic below)—seemed to offer the best compromise for rail application.

The above configuration appears to be similar to the architecture of the commercial US Tier 4 locomotive engines. While details on the GE and EMD Tier 4 engines have not yet been published, both engines are believed to use donor cylinders as the source of EGR.

Both Caterpillar and GE are also working on developing natural gas fueled locomotive engines. Both companies are pursuing dual fuel approaches where natural gas is inducted with the intake air and a diesel spray is used for ignition [ICEF2015-1119][ICEF2015-1077]. GE is investigating a strategy with very early diesel injection (RCCI).

A low emission upgrade kit for a 1.5 MW EMD GP20D switch locomotive was presented by SwRI [ICEF2015-1133]. The locomotive, powered by a Caterpillar 3516 Tier 1 engine, was upgraded to Tier 3 emissions to meet the requirements of California San Pedro Bay Ports. NOx was reduced from 6.4 g/bhp-hr to below 5 g using retarded fuel injection timing. PM emissions were reduced from from 0.33 g.bhp-hr to 0.03 g using a catalyzed, passively regenerated diesel particulate filter (2 times six DPF elements of 304 mm diameter x 254 mm length). The locomotive was also fitted with a CCV system. After the upgrade, PM emissions were reduced by 98%, CO/HC by 99% and NOx by 23%. Two locomotives equipped with the upgrade kit entered revenue service in December 2014.

Waste Heat Recovery. FEV conducted an interesting study of waste heat recovery for a US EPA Tier 4 locomotive engine using the organic Rankine cycle (ORC) [ICEF2015-1015]. In the analyzed system, the EGR cooler was replaced with an EGR evaporator and a turbine expander with 60% efficiency was used. The working fluid was ethanol under a working pressure of 30 bar. Thermodynamic calculations showed that for a 3-3.5 MW engine, a fuel economy improvement of 6-7% was achievable over the EPA and ARR line haul cycles. A similar energy recovery would be possible using the tailpipe exhaust gas stream rather than EGR. The investment cost of the ORC system could be recovered after a period of 13-26 months, depending on the fuel price. The main challenges in the application of ORC waste heat recovery to locomotive engines include the size of the components and system packaging.

A concept for waste heat recovery for light-duty hybrid vehicles was presented by Fraunhofer ICT and MOT GmbH [ICEF2015-1096]. Light-duty vehicles are a particularly challenging application for waste heat recovery because of exhaust low temperatures and relatively short driving cycles often dominated by cold start conditions. In this study, exhaust waste heat is recovered from the internal combustion engine using a Rankine cycle with water as the working fluid. However, an insulated steam accumulator is used for storage of the discontinuously available exhaust waste heat from the ICE. The insulated accumulator allows heat recovered during a previous drive cycle to be stored for up to several hours. Upon engine start-up, steam from the accumulator is fed to a expander/generator that produces electrical power that is fed into the vehicle’s electrical system. Steam from the outlet of the expander is further cooled by engine coolant; allowing the some engine preheating when the expander is used during a cold start. To quantify the benefits of this approach, a simulation study was carried out of a 1400 kg C-segment vehicle operating over the NEDC - a particularly challenging drive cycle for waste heat recovery. Using a micro hybrid drivetrain as a baseline, fuel consumption and CO₂ emissions for a parallel mild hybrid as well as a parallel mild hybrid with waste heat recovery were determined. These are summarized in the table below. Combining WHR with a mild hybrid drivetrain resulted in a 20% benefit over the base vehicle. The accumulator was assumed to be fully heated upon cold start. No estimates of cost were provided.

Controls. With the need for more precise control of combustion, some manufacturers are turning to cylinder pressure sensors to help control combustion parameters such as combustion phasing. Controlling cyclic variations would require that multiple cylinders be fitted with pressure sensors. However, cylinder pressure sensors are costly and this has limited their application. The University of Bologna and Magneti Marelli presented an alternative approach for sensing combustion phasing from multiple cylinders that requires only two crankshaft speed sensors—one mounted on each end of the crankshaft [ICEF2015-1099]. The approach relies on the torsional behaviour of the crankshaft. The difference in speed sensed by the two speed sensors is related to the torque applied to the crankshaft by a firing cylinder. Signal processing can be used to extract the instantaneous torsion applied to the crankshaft and from this, the combustion phasing. Testing on a 4 cylinder diesel engine showed that the approach worked well for the two cylinder furthest from the flywheel. However, for the two cylinders closest to the flywheel, damping from the flywheel resulted in a signal to noise ratio that was too low for accurate estimation of combustion phasing.

With advanced combustion strategies, cyclic variations can often limit the range over which these strategies can be applied. If it were possible to actively control cyclic variations, it may be possible to expand the application range of these advanced combustion strategies. This issue was examined by researchers at the University of Michigan [ICEF2015-1173]. If cyclic variations have an underlying deterministic pattern, it may be possible to use active control of injection timing or spark timing to reduce these variations. On the other hand, if the underlying variations are random, switching to a different combustion mode may be required. The researchers were able to quantify whether an underlying series of combustion phasing measurements was random or deterministic using statistical techniques called Shannon’s Entropy and “permutation entropy”; opening the door to potentially allowing active control techniques to be used to control cyclic variations.

Emission Aftertreatment. Researchers from the Tokyo University [ICEF2015-1038] investigated the phenomenon of soot layer separation from the DPF wall and collapse into the channel, which can cause a sudden increase of DPF pressure drop—an investigation that built on a study published last year by a team from General Motors. A visualization method was developed to observe the phenomenon in real time, using a DPF where a number of channels were cut open and observed through attached heat resistant glass. A test cycle was developed to invoke the soot layer collapse, and the phenomenon was photographed and filmed.

A study by Filter Sensing Technologies and Oak Ridge [A. Sappok., ICEF2015-1146] investigated the use of biodiesel blends (B0, B20, B100) with a light-duty diesel engine equipped with a catalyzed particulate filter and radio frequency sensor (RF) for the detection of the DPF soot load. DPF loading cycles were developed and used to preload the DPF to a soot level of 6 g/L and 4 g/L. Measurements of the PM oxidation rates using the RF sensor indicated more rapid oxidation of biodiesel-derived PM relative to petroleum-derived PM. The results demonstrated that the in-situ soot sensing strategy could deliver fuel savings through optimized DPF regeneration—longer time intervals between regenerations and shorter regeneration events—with the more reactive soot.

There is a growing interest in catalysts for the control of methane emissions—a powerful climate forcing agent—from stationary engines. While oxidation catalysts have been used to oxidize methane in lean burn engine exhaust, CH₄ is a highly stable compound and high activation energy (high catalyst temperature) is needed to break the C-H bond. Among the various types of catalysts, palladium formulations provide the highest CH₄ conversions. However, Pd is sensitive to sulfur poisoning—flue gases containing as little as 1 ppm SO2 can deactivate a Pd catalyst within days. DCL International has developed a sulfur trap [ICEF2015-1118] to protect Pd catalysts and extend the catalyst life. The sulfur trap utilizes porous mixed metal oxide that bounds sulfur in the form of sulphates. The trap can extend the catalyst life by up to 50 times. In applications with high sulfur gaseous fuels, such as biogas, the fuel must be still pre-treated with suitable sulfur adsorbents such as activated carbon.

Emission Testing and OBD. California OBD regulations require monitoring of the oxygen sensor (such as the UEGO sensor) upstream of the three-way catalyst in spark ignited engines. To satisfy these requirements, Ford developed a software strategy to monitor the UEGO sensor and introduce signal corrections in case a fault is detected [ICEF2015-1026].The algorithm uses a statistical approach to detect six types of faults—such as delays or lags in the lean/rich transitions—that can potentially occur in an oxygen sensor. The strategy does not require modifying the controller structure and only adapts the baseline gains of the controller and delay compensator to match the actual system dynamics. The strategy was demonstrated on a Mustang V6 3.7L vehicle where sensor faults were induced, showing a significant improvement in emissions.

A paper by the Technical University of Denmark discussed the development of an engine bench test to simulate chassis dynamometer cycles, including the NEDC, FTP-75 and WLTP. The chassis cycles were simulated in the engine test bench using two approaches: (1) a transient engine test where the inertia of the vehicle during deceleration was simulated by addition of power from an electric motor mounted on the crankshaft, and (2) steady state measurements where the total driving pattern was simulated from an integration of multiple steady state measurements. The transient method allowed, with minor deviations, to simulate the NEDC chassis dynamometer emission measurements.

Other Topics. Fouling of EGR coolers continues to receive attention, and the problem is likely to become even more important in engines meeting future low NOx emission standards, where more aggressive EGR strategies may be needed to control cold start emissions. EGR is also increasingly used to improve efficiency of gasoline engines and to enable advanced combustion modes. A study by US DOE ARPA-E and partners [ICEF2015-1110] presented experimental data from an in-situ measurement study in an EGR cooler visualization rig (University of Michigan) during the development of a 378 micron thick carbon nanoparticle based deposit layer. The results showed a non-linear deposit growth as well as an asymptotic increase in surface area of 20% compared to a flat surface. Deposit surface temperature and the temperature difference across the thickness of the layer increased with deposit thickness, and as a result lowered the heat transfer through the layer. The study quantified the composition and thermophysical properties of the deposit layer, such as the thermal conductivity. Volatile content had a large effect on the heat capacity of the cooler deposits, with a subsequent impact on EGR cooler effectiveness models.

Diesel engine combustion generated noise under steady-state operation has traditionally been correlated strongly with the maximum rate of cylinder pressure rise during the combustion event. This has typically been the case with both single injections and multiple injections. Recently, researchers at Sandia and GM have noted that significant noise reductions are possible within a narrow range of pilot/main injection separation in the range of 100-200 μs . At these short separations, combustion generated noise reductions do not correlate with changes in the maximum rate of cylinder pressure rise. Instead, noise reductions appear to be caused by an interference-type phenomena between the noise from the pressure rise from the pilot injection and that from the main injection pressure rise partially canceling each other out [ICEF2015-1004].

Dilution of crankcase oil with fuel has been a known challenge for not only diesel engines but GDI engines as well. Investigators from Ford have examined this issue more closely as it can be a source of control challenges for future GDI engines [ICEF2015-1072]. EGR control using a wide range oxygen sensor (UEGO) mounted in the intake system can be affected as fuel vapor is released from the crankcase oil and reinducted into the engine via the PCV system. After running a series of cycles intended to accumulate fuel in the crankcase lubricant, it was possible to reach fuel dilution levels as high as 10-15%. At the end of accumulation cycles, no light gasoline ends (i.e., components with a boiling temperature lower than about 100°C) were present in oil. After the accumulation phase, the engine was operated under prolonged conditions of warmed-up operation with the intend to drive off as much of the accumulated fuel as possible. This caused the mid-ends (components with boiling temperature between 100 and 150°C) to leave the oil via a slow vapour pressure driven process. Even after prolonged operation of 12 h, it was not possible to remove all the fuel components from the oil. A dilution level of about 4% remained; consisting mainly of gasoline components with a boiling temperature >150°C [ICEF-1072].

Researchers from the University of Minnesota [ICEF2015-1067] investigated emissions from a John Deere 4045 HF475 Tier 2 diesel engine fitted with an aftermarket dual fuel kit that allowed port injection of hydrous ethanol (the study was co-funded by the Minnesota Corn Growers Association). The dual fuel system incorporated port fuel injection (PFI) of hydrous ethanol (90% by vol.) and a heat exchanger to heat the ethanol to a range of 46-79°C to improve fuel vaporization in the intake port. It was found that ethanol substitution rates up to 37% were possible based on the fumigant energy fraction (FEF). As FEF increased, NO emissions decreased, but the NO reduction was balanced by an increase in NO₂ emissions, with marginal effects on total NOx. Emissions of CO, THC, and ethanol all increased with the FEF. Preheating the ethanol using engine coolant prior to injection had little benefit on engine-out emissions. Overall, the study found that the ethanol dual-fuel kit provided no emission benefit.

The results of an experimental study on in-cylinder NOx control via water injection were presented by Nostrum Energy [ICEF2015-1122]. Experiments were conducted in a light-duty 1.9 L Volkswagen diesel engine with water injection into the engine air inlet ports using 25, 50, 75 and 100% water relative to diesel fuel. A synergy was found between the effects of water injection and EGR. A 35% NOx reduction could be achieved using water alone (1:1 ratio), compared to a 92% reduction using water and 30% EGR.

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The 2016 Internal Combustion Engine Fall Technical Conference (ICEF 2016) will be held on October 9-12, 2016 in Greenville, South Carolina and hosted by Clemson University International Center for Automotive Research (CU-ICAR).

Conference website: www.asmeconferences.org/ICEF2015