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The California Air Resources Board (CARB)-funded Stage 3 Heavy-Duty Low NOX program focusses on evaluating different engine and after-treatment technologies to achieve 0.02g/bhp-hr of NOX emission over certification cycles. This paper highlights the controls architecture of the engine and after-treatment systems and discusses the effects of various strategies implemented and tested in an engine test cell over various heavy-duty drive cycles. A Cylinder De-Activation (CDA) system enabled engine was integrated with an advanced after-treatment controller and system package. Southwest Research Institute (SwRI) had implemented a model-based controller for the Selective Catalytic Reduction (SCR) system in the CARB Stage 1 Low-NOX program. The chemical kinetics for the model-based controller were further tuned and implemented in order to accurately represent the reactions for the catalysts used in this program.

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 new diesel engine system adopting alternative combustion with rich and near rich combustion, and an airflow-dominant control system for precise combustion control was used with a 4-way catalyst system with LNT (lean NOx trap) to achieve Tier II Bin 5 on a 2.2L TDI diesel engine. The study included catalyst temperature control, NOx regeneration, desulfation, and PM oxidation with and without post injection. Using a mass-produced lean burn gasoline LNT with 60,000 mile equivalent aging, compliance to Tier II Bin 5 emissions was confirmed for the US06 and FTP75 test cycles with low NVH, minor fuel penalty and smooth transient operation.

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 combination of premixed charge compression ignition (PCCI) and conventional DI diesel combustion was studied on a light-duty diesel engine equipped with EGR and a common rail fuel injection system. This combustion mode is referred to as PCCI-DI combustion. The main objectives of the study were to examine the emissions, performance and combustion characteristics of the engine operating under various levels of PCCI-DI combustion to determine if this mode of combustion was a viable in-cylinder NOX emissions reduction strategy. The premixed charge was obtained with early pilot injections (up to three) using a custom engine controller. The engine test conditions were limited to light and medium loads and moderate engine speeds. Engine tests consisted of sweeps of pilot injection timing and quantity, and number of pilot injections.

The use of small-hole diesel injector tips and high injection pressures was investigated as a countermeasure to the increased particulate matter (PM) emissions formed when using exhaust gas recirculation (EGR) in diesel engines. This study examined the use of injector tip hole sizes down to about 0.09-mm (0.0035 in.), and injection pressures to 300 MPa (3000 bar, or 43,500 psi). The first phase of these studies was conducted in a high-temperature, high-pressure combustion bomb, with supporting calculations using a unit injector model, a jet-mixing model, and a diesel jet evaporation model. The second phase was conducted in a commercial diesel engine of 12.7-liter displacement designed to meet U.S. 1998 emissions levels. Engine tests were conducted with a baseline cam and a faster rise-rate cam, and three different hole tip sizes. The cams consisted of a baseline cam and a cam of similar design, but with a 12 percent faster rise rate.

An experimental investigation of the effects of partial premixed charge compression ignition (PCCI) combustion and EGR temperature was conducted on a Caterpillar C-12 heavy-duty diesel engine (HDDE). The addition of EGR and PCCI combustion resulted in significant NOx reductions over the AVL 8-mode test. The lowest weighted BSNOx achieved was 2.55 g/kW-hr (1.90 g/hp-hr) using cooled EGR and 20% port fuel injection (PFI). This represents a 54% reduction compared to the stock engine. BSHC and BSCO emissions increased by a factor of 8 and 10, respectively, compared to the stock engine. BSFC also increased by 7.7%. In general, BSHC, BSCO, BSPM, and BSFC increased linearly with the amount of port-injected fuel.

For the US market, an abundant supply of natural gas (NG) coupled with recent green-house gas (GHG) regulations have spurred renewed interest in dual-fuel combustion regimes. This paper explores the potential of co-direct injection to improve the efficiency and reduce the methane emissions versus equivalent fumigated dual-fuel combustion systems. Using the Westport HPDI engine as the experimental test platform, the paper reports the results obtained using both diffusion controlled (HPDI) combustion strategy as well as a partially-premixed combustion strategy (DI2). The DI2 combustion strategy shows good promise, as it has been found to improve the engine efficiency by over two brake thermal efficiency (BTE) points (% fuel energy) compared to the diffusion controlled combustion strategy (HPDI) while at the same time reducing the engine-out methane emissions by 75% compared to an equivalent fumigated dual-fuel combustion system.

The CO2 advantage coupled with the low NOX and PM potential of natural gas (NG) makes it well-suited for meeting future greenhouse gas (GHG) and NOX regulations for on-road medium and heavy-duty engines. However, because NG is mostly methane, reduced combustion efficiency associated with traditional NG fueling strategies can result in significant levels of methane emissions which offset the CO2 advantage due to reduced efficiency and the high global warming potential of methane. To address this issue, the unique co-direct injection capability of the Westport HPDI fuel system was leveraged to obtain a partially-premixed fuel charge by injecting NG during the compression stroke followed by diesel injection for ignition timing control. This combustion strategy, referred to as DI2, was found to improve thermal and combustion efficiencies over fumigated dual-fuel combustion modes.

This paper explores the possibility of on-board fuel classification for fuel property adaptive compression-ignition engine control system. The fuel classifier is designed to on-board classify the fuel that a diesel engine is running, including alternative and renewable fuels such as bio-diesel. Based on this classification, the key fuel properties are provided to the engine control system for optimal control of in-cylinder combustion and exhaust treatment system management with respect to the fuel. The fuel classifier employs engine input-output response characteristics measured from standard engine sensors to classify the fuel. For proof-of-concept purposes, engine input-output responses were measured for three different fuels at three different engine operating conditions. Two neural-network-based fuel classifiers were developed for different classification scenarios. Of the three engine operating conditions tested, two conditions were selected for the fuel classifier to be active.

The aim of this study was to establish a fully capable diesel exhaust treatment system (4-way catalyst system) based on a catalyzed diesel particulate filter (cDPF) and a Lean NOx trap (LNT) for meeting US Tier 2 emissions. In this study, two modified combustion technologies, LTC (Low Temperature Combustion) and PCCI (Premixed Controlled Compression Ignition), were used and improved to achieve high catalyst bed temperatures and to provide rich exhaust gas with low smoke to utilize a 4-way catalyst system. The LTC operation area was expanded to both lower and higher loads using a dual loop EGR system (high-and low-pressure-loop EGR). The effect of air-fuel ratio, injection timing, and intake manifold temperature on combustion stability and soot emissions of LTC were investigated. PCCI, characterized by increased and advanced pilot injection, combined with retarded main injection timings and without EGR was used to achieve low-smoke, rich combustion at medium loads.

Reactivity Controlled Compression Ignition (RCCI) natural gas/diesel dual-fuel combustion has been shown to achieve high thermal efficiency with low NOX and PM emissions, but has traditionally been limited to low to medium loads. High BMEP operation typically requires high substitution rates (i.e., >90% NG), which can lead to high cylinder pressure, pressure rise rates, knock, and combustion loss. In previous studies, compression ratio was decreased to achieve higher load operation, but thermal efficiency was sacrificed. For this study, a multi-cylinder heavy-duty engine that has been modified for dual-fuel operation (diesel direct-injection and natural gas (NG) fumigated into the intake stream) was used to explore RCCI and other dual-fuel combustion modes at high compression ratio, while maintaining stock lug curve capability (i.e., extending dual-fuel operation to high loads where conventional diesel combustion traditionally had to be used).