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Work was performed to determine the feasibility of operating heavy-duty natural gas engines over a wide range of fuel compositions by evaluating engine performance and emission levels. Heavy-duty compressed natural gas engines from various engine manufacturers, spanning a range of model years and technologies, were evaluated using a diversity of fuel blends. Performance and regulated emission levels from these engines were evaluated using natural gas fuel blends with varying methane number (MN) and Wobbe Index in a dynamometer test cell. Eight natural gas blends were tested with each engine, and ranged from MN 75 to MN 100. Test engines included a 2007 model year Cummins ISL G, a 2006 model year Cummins C Gas Plus, a 2005 model year John Deere 6081H, a 1998 model year Cummins C Gas, and a 1999 model year Detroit Diesel Series 50G TK. All engines used lean-burn technology, except for the ISL G, which was a stoichiometric engine.

The diesel engine can be an effective solution to meet future greenhouse gas and fuel economy standards, especially for larger segment vehicles. However, a key challenge facing the diesel is the upcoming LEV III and Tier 3 emission standards which will require significant reductions in hydrocarbon (HC) and oxides of nitrogen (NOx) emissions. The challenge stems from the fact that diesel exhaust temperatures are much lower than gasoline engines, so the time required to achieve effective emissions control after a cold-start with typical aftertreatment devices is considerably longer. To address this challenge, a novel diesel cold-start emission control strategy was investigated on a 2L class diesel engine. This strategy combines several technologies to reduce tailpipe HC and NOx emissions before the start of the second hill of the FTP75. The technologies include both engine tuning and aftertreatment changes.

A push for more stringent emissions regulations has resulted in larger, increasingly complex aftertreatment solutions. In particular, oxides of nitrogen (NOX) and particulate matter (PM) have been controlled using two separate systems, selective catalytic reduction (SCR) and the catalyze diesel particulate filter (CDPF), or the functionality has been combined into a single device producing the SCR on filter (SCRoF). The SCRoF forgoes beneficial NO2 production present in the CDPF to avoid NH3 oxidation which occurs when using platinum group metals (PGM) for oxidation. In this study, mixed-metal oxides are shown to oxidize NO to NO2 without appreciable NH3 oxidation. This selectivity leads to enhanced performance when combined with a typical Cu-zeolite catalyst.

The most recent 2010 emissions standards for heavy-duty engines have established a tailpipe limit of oxides of nitrogen (NOX) emissions of 0.20 g/bhp-hr. However, it is projected that even when the entire on-road fleet of heavy-duty vehicles operating in California is compliant with 2010 emission standards, the National Ambient Air Quality Standards (NAAQS) requirement for ambient particulate matter and Ozone will not be achieved without further reduction in NOX emissions. The California Air Resources Board (CARB) funded a research program to explore the feasibility of achieving 0.02 g/bhp-hr NOX emissions.

In-cylinder emission controls were the focus for diesel engines for many decades before the emergence of diesel aftertreatment. Even with modern aftertreatment, control of in-cylinder processes remains a key issue for developing diesel vehicles with low tailpipe emissions. A reduction in in-cylinder emissions makes aftertreatment more effective at lower cost with superior fuel economy. This paper describes a study focused on an in-cylinder combustion control approach using a Delphi E3 flexible fuel system to achieve low engine-out NOx and PM emissions. A 2003 model year Detroit Diesel Corporation Series 60 14L heady-duty diesel engine, modified to accept the Delphi E3 unit injectors, and ultra low sulfur fuel were used throughout this study. The process of achieving premixed low temperature combustion within the limited range of parameters of the stock ECU was investigated.

Nitrous Oxide (N₂O) is a greenhouse gas with a Global Warming Potential (GWP) of 298-310 (298-310 times more potent than carbon dioxide (CO₂)). As a result, any aftertreatment system that generates N₂O must be well understood to be used effectively. Under low temperature conditions, N₂O can be produced by Selective Catalytic Reduction (SCR) catalysts. The chemistry is reasonably well understood with N₂O formed by the thermal decomposition of ammonium nitrate. Ammonium nitrate and N₂O form in oxides of nitrogen (NOx) gas mixtures that are high in nitrogen dioxide (NO₂). This mechanism occurs at a relatively low temperature of about 200°C, and can be controlled by maintaining the nitric oxide (NO)/NO₂ ratio above 1. However, N₂O has also been observed at relatively high temperatures, in the region of 500°C.

Experiments were performed on a 2.4L boosted, MPI gasoline engine, equipped with a low-pressure loop (LPL) cooled EGR system and an advanced ignition system, using fuels with varying anti-knock indices. The fuels were blends of 87, 93 and 105 Anti-Knock Index (AKI) gasoline. Ignition timing and EGR sweeps were performed at various loads to determine the tradeoff between EGR level and fuel octane rating. The resulting engine data was analyzed to establish the relationship between the octane requirement and the level of cooled EGR used in a given application. In addition, the combustion difference between fuels was examined to determine the effect that fuel reactivity, in the form of anti-knock index (AKI), has on EGR tolerance and burn rate. The results indicate that the improvement in effective AKI of the fuel from using EGR is constant across commercial grade gasolines at about 0.5 ON per % EGR.

A 13 L HD diesel engine was converted to run as a flame propagation engine using the HEDGE™ Dual-Fuel concept. This concept consists of pre-mixed gasoline ignited by a small amount of diesel fuel - i.e., a diesel micropilot. Due to the large bore size and relatively high compression ratio for a pre-mixed combustion engine, high levels of cooled EGR were used to suppress knock and reduce the engine-out emissions of the oxides of nitrogen and particulates. Previous work had indicated that the boosting of high dilution engines challenges most modern turbocharging systems, so phase I of the project consisted of extensive simulation efforts to identify an EGR configuration that would allow for high levels of EGR flow along the lug curve while minimizing pumping losses and combustion instabilities from excessive backpressure. A potential solution that provided adequate BTE potential was consisted of dual loop EGR systems to simultaneously flow high pressure and low pressure loop EGR.

The diesel engine can be an effective solution to meet future greenhouse gas and fuel economy standards, especially for larger segment vehicles. However, a key challenge facing the diesel is the upcoming LEV III emissions standard which will require significant reductions of hydrocarbon (HC) and oxides of nitrogen (NOx) from current levels. The challenge stems from the fact that diesel exhaust temperatures are much lower than gasoline engines so the time required to achieve effective emissions control with current aftertreatment devices is considerably longer. The objective of this study was to determine the potential of a novel diesel cold-start emissions control strategy for achieving LEV III emissions. The strategy combines several technologies to reduce HC and NOx emissions before the start of the second hill of the FTP75.

A high-efficiency NOx aftertreatment system has been proposed for use in Diesel engines. This system includes a Lean NOx Trap (LNT) in series with a Selective Catalyst Reduction (SCR) catalyst [6], [7], [8], and is hereinafter referred to as the LNT-SCR system. The combined LNT-SCR system can potentially overcome many of the drawbacks of LNT-only and SCR-only operation and achieve very high NOx conversion efficiency without external addition of ammonia (or urea). A laboratory test procedure was developed to validate the LNT-SCR system concept, and a series of tests was conducted to test the NOx conversion of this system under various conditions. A Synthetic Gas Reactor (SGR) system was modified to accommodate LNT and SCR catalyst cores and synthetic gas mixtures were used to simulate rich-lean regeneration cycles from a diesel engine. A Fourier Transform Infrared (FTIR) system was used to measure gas compositions within the LNT-SCR system.

The minimum oxides of nitrogen (NOx) emissions over the U.S. Federal Test Procedure (FTP) using exhaust gas recirculation (EGR) were investigated on a heavy-duty diesel engine featuring a pump-line-nozzle fuel injection system. Due to the technical merits of electronic fuel injection systems, most accounts of EGR system development for heavy-duty diesel engines have focused on these types of engines and not engines with mechanical fuel systems. This work details use of a high-pressure-loop EGR configuration and a novel, computer-controlled, EGR valve that allowed for optimizing the EGR rate as a function of speed and load on a 6L, turbo-charged/intercooled engine. Cycle NOx levels were reduced nearly 50 percent to 2.3 g/hp-hr using conventional diesel fuel and application of only EGR, but particulates increased nearly three-fold even with the standard oxidation catalyst employed.

The goal of this project was to demonstrate a low emissions, high efficiency heavy-duty on-highway natural gas engine. The emissions targets for this project are to demonstrate US 2010 emissions standards on the 13-mode steady state test. To meet this goal, a chemically correct combustion (stoichiometric) natural gas engine with exhaust gas recirculation (EGR) and a three way catalyst (TWC) was developed. In addition, a Sturman Industries, Inc. camless Hydraulic Valve Actuation (HVA) system was used to improve efficiency. A Volvo 11 liter diesel engine was converted to operate as a stoichiometric natural gas engine. Operating a natural gas engine with stoichiometric combustion allows for the effective use of a TWC, which can simultaneously oxidize hydrocarbons and carbon monoxide and reduce NOx. High conversion efficiencies are possible through proper control of air-fuel ratio.

A zero-dimensional cycle simulation model coupled with a chemical equilibrium model and a two-zone combustion model has been extended to predict nitric oxide formation and emissions from spark-ignited, lean-burn natural gas engines. It is demonstrated that using the extended Zeldovich mechanism alone, the NOx emissions from an 8.1-liter, 6-cylinder, natural gas engine were significantly under predicted. However, by combining the predicted NOx formation from both the extended Zeldovich thermal NO and the Fenimore prompt NO mechanisms, the NOx emissions were predicted with fair accuracy over a range of engine powers and lean-burn equivalence ratios. The effect of injection timing on NOx emissions was under predicted. Humidity effects on NOx formation were slightly under predicted in another engine, a 6.8-liter, 6-cylinder, natural gas engine. Engine power was well predicted in both engines, which is a prerequisite to accurate NOx predictions.

A new on-board portable emission measurement system (PEMS) for gaseous emissions has been designed and developed to meet CFR Part 1065 requirements. The new system consists of a heated flame ionization detector (HFID) for the measurement of total hydrocarbon, a heated chemiluminescence detector (HCLD) for the measurement of NOx, and a heated non-dispersive infra-red detector (HNDIR) for the measurement of CO and CO2. The oxygen interference and relative sensitivity of several hydrocarbon components have been optimized for the HFID. The CO2 and H2O quenching effect on the HCLD have been compensated using measured CO2 and H2O concentration. The spectral overlap and molecular interaction of H2O on the HNDIR measurement has also been compensated using an independent H2O concentration measurement. The basic performance of the new on-board emission measurement system has been verified accordingly with CFR part 1065 and all of the performances have met with CFR part 1065 requirement.

A system for injection of diesel fuel and water with real-time control, or real-time water injection (RTWI), was developed and applied to a heavy-duty diesel engine. The RTWI system featured electronic unit pumps that delivered metered volumes of water to electronic unit injectors (EUI) modified to incorporate the water addition passages. The water and diesel mixed in the injector tip such that the initial portion of the injection contained mostly diesel fuel, while the balance of the injection was a water and diesel mixture. With this hardware, real-time cycle-by-cycle control of water mass was used to mitigate soot formation during diesel combustion. Using RTWI alone, NOx emissions were reduced by 42%. Using high-pressure-loop exhaust gas recirculation (EGR) and conventional diesel combustion with RTWI, the NOx was reduced by 82%.

The engine selected for this work was a Caterpillar 3176 engine. Engine exhaust emissions, performance, and heat release rates were measured as functions of engine configuration, engine speed and load. Two engine configurations were used, a standard 1994 design and a 1994 configuration with EGR designed to achieve a NOx emissions level of 2.5 gm/hp-hr. Measurements were performed at 7 different steady-state, speed-load conditions on thirteen different test fuels. The fuel matrix was statistically designed to independently examine the effects of the targeted fuel properties. Cetane number was varied from 40 to 55, using both natural cetane number and cetane percent improver additives. Aromatic content ranged from 10 to 30 percent in two different forms, one in which the aromatics were predominantly mono-aromatic species and the other, where a significant fraction of the aromatics were either di- or tri-aromatics.

The US EPA emission standards for 2010 on-highway and 2014 non-road diesel engines are extremely stringent, both in terms of oxides of nitrogen (NOX) and particulate matter (PM). Diesel engines typically operate lean and use at least 40-50 percent more air than what is needed for stoichiometric combustion of the fuel. As a result, significant excess oxygen (O₂) is present in diesel exhaust gas which prevents the application of the mature three-way catalyst (TWC) technology for NOX control used in gasoline engines. The objective of this work was to investigate whether or not the catalyzed DPF had a TWC-type of effect on NOX emissions and if so, why and to what extent when used on a diesel engine operating at reduced A/F ratio conditions.

The Texas Department of Transportation began using an emulsified diesel fuel in 2002. They initiated a simultaneous study of the effectiveness of this fuel in comparison to 2D on-road diesel fuel and 2D off-road diesel. The study included comparisons of fuel economy and emissions for the emulsion, Lubrizol PuriNOx®, relative to conventional diesel fuels. Two engines and eight trucks, four single-axle dump trucks, and four tandem-axle dump trucks were tested. The equipment tested included both older mechanically-controlled diesels and newer electronically-controlled diesels. The two engines were tested over two different cycles that were developed specifically for this project. The dump trucks were tested using the “route” technique over one or the other of two chassis dynamometer cycles that were developed for this project In addition to fuel efficiency, emissions of NOx, PM, CO, and HCs were measured. Additionally, second-by-second results were obtained for NOx and HCs.

The 2007 emission standards for both light-duty and heavy-duty diesel vehicles remain a challenge. A level of about 90% NOx conversion is required to meet the standards. Technologies that have the most potential to achieve very high NOx conversion at low temperatures of diesel exhaust are lean NOx traps (LNTs) and Selective Catalytic Reduction (SCR) of NOx using aqueous urea, typically known as Urea SCR. The LNT has the advantage of requiring no new infrastructure, and does not pose any new customer compliance issues. However, Urea SCR has high and durable NOx conversion in a wider temperature window, a lower equivalent fuel penalty, and lower system cost. On a technical basis, Urea SCR has the best chance of meeting the 2007 NOx targets. This paper reviews the results of some demonstration programs for both light-and heavy-duty applications.

Results of engine bench tests on a 1998 heavy-duty diesel engine have confirmed the emissions reduction performance of a U.S. Environmental Protection Agency (EPA) registered platinum/cerium bimetallic fuel borne catalyst (FBC) used with several different catalyzed and uncatalyzed diesel particulate filters (DPF's). Performance was evaluated on both a 450ppm sulfur fuel (No.2 D) and a CARB 50ppm low sulfur diesel (LSD) fuel. Particulate emissions of less than 0.02g/bhp-hr were achieved on several combinations of FBC and uncatalyzed filters on 450ppm sulfur fuel while levels of 0.01g/bhp-hr were achieved for both catalyzed and uncatalyzed filters using the FBC with the low sulfur CARB fuel. Eight-mode steady state testing of one filter and FBC combination with engine timing changes produced a 20% nitrogen oxide (NOx) reduction with particulates (PM) maintained at 0.01g/bhp-hr and no increase in measured fuel consumption.