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Selective Catalytic Reduction is the primary method of NOX emission abatement in lean-burn internal combustion. This process requires the decomposition of a 32.5 wt. % urea-water solution (UWS) to provide ammonia as a reducing agent for NOX, but at temperatures < 250 °C the injection of UWS is limited due to the formation of harmful deposits within an aftertreatment system and decreased ammonia production. Previous work has sufficiently demonstrated that the addition of surfactant and a urea/isocyanic acid (HNCO) decomposition catalyst to UWS can significantly decrease deposit formation within an aftertreatment system. The objective of this work was to further optimize the modified UWS formulation by investigating different types and concentrations of surfactants and titanium-based urea/HNCO catalyst. Because there is a correlation between surface tension and water evaporation, it was theorized that minimizing the surface tension of UWS would result in decreased deposit formation.

Commercial vehicles are moving in the direction of improving brake thermal efficiency while also meeting future diesel emission requirements. This study is focused on improving efficiency by replacing the variable geometry turbine (VGT) turbocharger with a high-efficiency fixed geometry turbocharger. Engine-out (EO) NOX emissions are maintained by providing the required amount of exhaust gas recirculation (EGR) using a 48 V motor driven EGR pump downstream of the EGR cooler. This engine is also equipped with cylinder deactivation (CDA) hardware such that the engine can be optimized at low load operation using the combination of the high-efficiency turbocharger, EGR pump and CDA. The exhaust aftertreatment system has been shown to meet 2027 emissions using the baseline engine hardware as it includes a close coupled light-off SCR followed by a downstream SCR system.

Simulating high amounts of exhaust gas recirculation in spark ignited engines to predict combustion using the currently available CFD modeling approaches is a challenge and does not always give reasonable matches with experimental observations. One of the reasons for the mismatch lies with the secondary circuit treatment of the ignition coil and the resulting energy deposition or a complete lack of it thereof. An ignition modeling approach is developed in this work which predicts the energy transfer from the electrical circuit to the gases in the combustion chamber leading to flame kernel growth under high EGR and high gas flow velocity conditions. Secondary circuit sub-model includes secondary side of the coil, spark plug and spark gap. The sub-model calculates the delivered energy to the gas based on given circuit properties and total initial electrical energy.

Increased electrification of future heavy-duty engines and vehicles can enable many new technologies to improve efficiency. Electrified oil pumps are one such technology that provides the ability to reduce or turn off the piston oil cooling jets and simultaneously reduce the oil pump flow to account for the reduced flow rate required. This can reduce parasitic losses and improve overall engine efficiency. In order to study the potential impact of reduced oil cooling, a GT-Power engine model prediction of piston temperature was calibrated based on measured piston temperatures from a wireless telemetry system. A simulation was run in which the piston oil cooling was controlled to target a safe piston surface temperature and the resulting reduction in oil cooling was determined. With reduced oil cooling, engine BSFC improved by 0.2-0.8% compared to the baseline with full oil cooling, due to reduced heat transfer from the elevated piston temperatures.

Water injection is an effective method for knock control in spark-ignition engines. However, the requirement of a separate water source and the cost and complexity associated with a fully integrated system creates a limitation of this method to be used in volume production engines. The engine exhaust typically contains 10-15% water vapor by volume which could be condensed and potentially stored for future use. In this study, the exhaust condensate composition was assessed for its use as an effective replacement for distilled water. Specifically, condensate samples were collected pre and post-three-way catalyst (TWC) and analyzed for acidity and composition. The composition of the pre and post-TWC condensates was found to be similar however, the pre-TWC condensate was mildly acidic. The mild acidity has the potential to corrode certain components in the intake air circuit.

The dedicated exhaust gas recirculation (D-EGR®) concept developed by Southwest Research Institute (SwRI) has demonstrated a thermal efficiency increase on several spark-ignited engines at both low and high-load conditions. Syngas (H2+CO) is produced by the dedicated cylinder (D-cyl) which operates at a rich air-fuel ratio. The syngas helps to stabilize combustion under highly dilute conditions at low loads as well as mitigating knock at high loads. The D-cyl produces all the EGR for the engine at a fixed rate of approximately 25% EGR for a four-cylinder engine and 33% EGR for a six-cylinder engine. The D-cyl typically runs up to an equivalence ratio of 1.4 for gasoline-fueled engines, beyond which the combustion becomes unstable due to the decreasing laminar burning velocity caused by rich conditions. Conventional active-fueled and passive pre-chambers have benefits of inducing multi-site ignition and enhancing turbulence in the main chamber.

The size and distribution of a vehicle’s tailpipe particulate emissions can have a strong impact on human health, especially if the particles are small enough to enter the human respiratory system. Gasoline direct injection (GDI) has been adopted widely to meet stringent fuel economy and CO2 regulations across the globe for recent engine architectures. However, the introduction of GDI has led to challenges concerning the particulate matter (PM) and particle number (PN) emissions from such engines. This study aimed to compare the particulate emissions of three SI combustion strategies: conventional SI, conventional stoichiometric low-pressure exhaust gas recirculation (LP-EGR), and Dedicated-EGR (D-EGR) at four specific test conditions. It was shown that the engine-out PM/PN for both the EGR strategies was lower than the conventional SI combustion under normal operating conditions. The test conditions were chosen to represent the WLTC test conditions.

In this study, a high-efficiency heavy-duty diesel engine platform was used to evaluate gasoline compression ignition (GCI) operation. The experiment was carried out using a single-cylinder engine (SCE) of a high compression ratio (22:1). Pump-grade gasoline fuel 87 research octane number (RON) was used throughout engine testing. Injection strategy was established including double and triple injection schemes to optimize both engine efficiency and emissions. Both low-temperature heat release (LTHR) and high-temperature heat release (HTHR) were seen from a two-stage combustion event resulting from the interaction of pilot and main injections. At low load conditions, besides fuel stratification level by pilot/main injection strategy, higher in-cylinder pressure can greatly improve the ignition of 1st stage combustion. As engine load increases, spray-wall interaction becomes more critical on engine efficiency and emissions performance.

Detailed characterization of particle emissions from three different engine technologies were performed, two of which were advanced technology engines. One of the engines was a nonroad Tier 4 Final emission regulation compliant 6.8L John Deere PSS 6068 diesel engine operated with its production calibration strategy. The other two engine platforms were advanced engine technologies whose controllers were developed by Southwest Research Institute (SwRI). These included a dual fuel Navistar MaxxForce 13L natural gas-diesel engine and a Cummins ISX 15L diesel engine. The dual fuel engine was operated in two distinct modes, conventional dual fuel (CDF) mode and low temperature reactivity controlled compression ignition (RCCI) mode. The Cummins ISX engine was operated using a “hot” or low EGR combustion strategy. For each engine technology, the test campaign involved steady-state test modes ranging from low speed low load to high speed high load conditions.

Current industry trends in both powertrain electrification and vehicle drag reduction point towards reduced peak and average power demands from the internal combustion engine in future long-haul class 8 vehicles. Downsizing the engine displacement to match these new performance requirements can yield a benefit in drive cycle efficiency through reduced friction and improved cruise load efficiency. Downsizing by reducing cylinder count avoids the heat loss and friction penalties from reduced per-cylinder displacement and could allow a manufacturer to continue to leverage the highly optimized combustion system from existing heavy-duty engines in the new downsized offering. The concept of this study is to leverage powertrain electrification and the improvement trends in vehicle aerodynamics and rolling resistance to develop a fuel economy focused, downsized heavy duty diesel powertrain for future long-haul vehicles utilizing a reduced cylinder count.

Particulate matter (PM) and NOX are two major pollutants generated by diesel engines. Modern diesel aftertreatment systems include selective catalytic reduction (SCR) technology that helps reduce tailpipe NOX emissions when coupled with diesel exhaust fluid (DEF/urea) injection. However, this process also results in the formation of urea derived byproducts that can influence non-volatile particle number (PN) measurement conducted in accordance with the European Union (EU) Particle Measurement Program (PMP) protocol. In this program, an experimental investigation of the impact of DEF injection on tailpipe PN and its implications for PMP compliant measurements was conducted using a 2015 model year 6.7 L diesel engine equipped with a diesel oxidation catalyst, diesel particulate filter and SCR system. Open access to the engine controller was available to manually override select parameters.

With the advancement of engine technologies and combustion strategies, aftertreatment architectures are expected to evolve as they continue to be the primary emissions mitigation hardware. Some of the engine approaches offer unique challenges and benefits that are not well understood beyond criteria pollutant emissions. As such, there continues to be a need to quantify engine emissions characteristics in pursuit of catalyst technology development and the use of advanced simulation tools. The following study discusses results from an extensive engine emissions assessment for current state-of-the-art technology and novel combustion regimes. The engines tested include a Tier 4 final compliant 6.8 L John Deere PSS 6068 diesel engine, a modified 15 L diesel engine, and a dual fuel 13 L natural gas-diesel engine. The dual fuel engine could operate in conventional positive ignition mode (CDF) or low temperature reactivity-controlled compression ignition mode (RCCI).

A computational fluid dynamics (CFD) model was developed to explore gasoline compression ignition (GCI) combustion. Results were validated with single-cylinder engine (SCE) experiments. It was shown that the CFD model captured experimental results well. Cylinder pressure, heat release and emissions from the CFD model were also used to analyze the performance of GCI combustion with a current heavy-duty diesel engine platform. This work also provides detailed analysis on in-cylinder combustion and emissions using CFD. It was found that multiple injection strategy can deliver desirable fuel stratification profile that benefits both engine and emissions performance. A wave contoured piston was compared with a stepped-lip type piston for both GCI and Diesel combustion scenarios on the same engine platform. Stepped-lip pistons offer an opportunity to use multiple injection strategies to overcome high UHC emissions of GCI combustion when compared to wave pistons.

Low-Speed pre-ignition (LSPI) in modern-day, heavily downsized, boosted, and direct-injection spark ignition (SI) engines is a well-known problem. Several mechanisms contribute towards stochastic pre-ignition (SPI), the most prominent being crevice material droplet induced and deposit induced pre-ignition mechanisms. The droplet mechanism is typically dominated by the detergent additives present in the lubricant formulation; more specifically calcium and sodium-based detergent additives correlate strongly with the increased LSPI rates. Deposits flaking off the combustion chamber surfaces can also induce LSPI under certain conditions. This study aimed to develop an optical method designed to investigate the nature of pre-ignition precursors. Southwest Research Institute (SwRI) utilized an optically accessible GM 2.0 L LHU engine to study the pre-ignition phenomenon and studied the nature of pre-ignition precursors using spectral information from one of the cylinders in this engine.

Low-Speed Pre-ignition (LSPI) is an undesirable abnormal combustion phenomenon observed in turbocharged, direct-injection spark-ignition engines and is characterized by early heat release, high cylinder pressures and severe, potentially damaging knock. LSPI has been studied for more than a decade and engine design, operating conditions and fuel and engine oil formulations have all been identified as contributing factors. A significant focus on engine oil has led to the establishment of the Sequence IX engine test and the second-generation of GM dexos® oil requirements, as well as a convergence of engine oil detergent causality. Conclusions about the effects of fuel on LSPI have been more varied, but as part of a recently completed research consortium, the LSPI tendency of market fuels with a range of properties, including composition, boiling point distribution, ethanol content and particulate matter index (PMI) were evaluated.

The confluence of increasing fuel economy requirements and increased use of ethanol as a gasoline blend component has led to various studies into the efficiency and performance benefits of higher octane numbers and high ethanol content fuels in modern engines. As part of a comprehensive study of the autoignition of different fuels in both the CFR octane rating engine and a modern, direct injection, turbocharged spark-ignited engine, a series of fuel blends were prepared with varying composition, octane numbers and ethanol blend levels. The paper reports on the third part of this study where cylinder pressures were recorded for fuels under knocking conditions in both a single-cylinder research engine (SCE), utilizing a GM LHU head and piston, as well as the CFR engines used for octane ratings.

Because of the thermodynamic relationship of pressure, temperature and volume for processes which occur in an internal-combustion engine (ICE), and their relationship to ideal efficiency and efficiency-limiting phenomena e.g. knock in spark-ignition engines, changing the thermo-chemical properties of the in-cylinder charge should be considered as an increment in the development of the ICE engine for future efficiency improvements. Exhaust gas recirculation (EGR) in spark-ignited gasoline engines is one increment that has been made to alter the in-cylinder charge. EGR gives proven thermal efficiency benefits for SI engines which improve vehicle fuel economy, as demonstrated through literature and production applications. The thermal efficiency benefit of EGR is due to lower in-cylinder temperatures, reduced heat transfer and reduced pumping losses. The next major increment could be modifying the constituents of the EGR stream, potentially through the means of a membrane.

As agencies and governing bodies evaluate the feasibility of reduced emission standards, additional focus has been placed on technology durability. This is seen in proposed updates, which would require Original Equipment Manufacturers (OEMs) to certify engine families utilizing a full useful life (FUL) aftertreatment system. These kinds of proposed rulings would place a heavy burden on the manufacturer to generate FUL components utilizing traditional engine aging methods. Complications in this process will also increase the product development effort and will likely limit the amount of aftertreatment durability testing. There is also uncertainty regarding the aging approach and the representative impact compared to field aged units. Existing methodologies have evolved to account for several deterioration mechanisms that, when controlled, can be utilized to create a flexible aging protocol. As a result, these methodologies provide the necessary foundation for continued development.

The worldwide trend of tightening CO2 emissions standards and desire for near zero emissions is driving development of high efficiency natural gas engines for a low CO2 replacement of traditional diesel engines. A Cummins Westport ISX12 G was previously converted to a Dedicated EGR® (D-EGR®) configuration with two out of the six cylinders acting as the EGR producing cylinders. Using a systems approach, the combustion and turbocharging systems were optimized for improved efficiency while maintaining the potential for achieving 0.02 g/bhp-hr NOX standards. A prototype variable nozzle turbocharger was selected to maintain the stock torque curve. The EGR delivery method enabled a reduction in pre-turbine pressure as the turbine was not required to be undersized to drive EGR. A high energy Dual Coil Offset (DCO®) ignition system was utilized to maintain stable combustion with increased EGR rates.

With the conclusion of the California Air Resources Board (CARB) Stage 1 Ultra-Low NOX program, there continues to be a commitment for identifying potential pathways to demonstrate 0.02 g/hp-hr NOX emissions. The Stage 1 program focused on achieving the Ultra-Low NOX (ULN) levels utilizing a turbo-compound (TC) engine, which required the integration of novel catalyst technologies and a supplemental heat source. While the aftertreatment configuration provided a potential solution to meet the ULN target, a complicated approach was required to overcome challenges from low temperature exhaust. The Stage 3 program leverages a different engine architecture more representative of the broader heavy-duty industry to meet the Phase 2 Greenhouse Gas (GHG) targets and to simplify the ULN aftertreatment solution. The following work will discuss the aftertreatment technology evaluation, down selection criteria, and the emission results for the candidate ULN systems