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To increase the efficiency of a natural gas engine, the use of a Miller camshaft was analysed. To avoid a decline in the low-end torque and also in the transient response, a pressure wave supercharger (Comprex™) was compared to the conventional single-stage turbocharger. The analyses for this conceptual comparison were performed experimentally, and the data were then used to run simulations of driving cycles for light commercial vehicles. A torque increase of 49% resulted at 1250 rpm when the Comprex™ was used in combination with a Miller camshaft. Despite the Miller camshaft, the Comprex™ transient response was still faster than the turbocharged engine. Using the same camshaft, the turbocharged engine took 2.5-times as long to reach the same torque. Water injection was used to increase the peak power output while respecting the temperature limitations. As the Comprex™ enables engine braking by design, we show that the use of friction brakes was reduced by two-thirds. Finally, a six-times faster catalyst warmup and an up to 90 °C higher exhaust gas temperature at the three-way catalytic converter added to the benefits of using the Comprex™ supercharger. The known drawbacks of the Comprex™ superchargers were solved due to a complete redesign of the machine, which is described in detail.

Diesel soot is a significant contributor to air pollution. Soot particles present in diesel engine exhaust have a negative impact on the environment and human health. Diesel oxidation catalysts (DOCs) and diesel particulate filters (DPFs) currently use noble metal-based catalysts for soot oxidation. Due to the use of noble metals in the catalyst, the cost of diesel after-treatment systems is steadily rising. As a result, diesel vehicles have become commercially less viable than gasoline vehicles and electronic vehicles. The study focuses on an alternative diesel oxidation catalyst with efficiency similar to that of a noble metal catalyst but with a much lower cost. CeO 2 -Al 2 O 3 catalysts are known for their oxygen storage capacity and high redox activity, making them suitable for soot oxidation. Adding Zr to these catalysts has been shown to influence their structural and chemical properties, significantly affecting their catalytic behavior. Therefore, the current study is focused on using Zr/CeO 2 -Al 2 O 3 as a substitute for noble metal-based catalysts to enhance its performance for diesel soot oxidation in automotive exhaust. Evaporation-induced self-assembly (EISA) was used to prepare 1, 3, and 5 weight (wt) % Zr supported mesoporous CeO 2 -Al 2 O 3 catalysts. Morphological, structural, and physicochemical properties of the synthesized catalysts were examined using Brunauer–Emmett–Teller (BET) absolute isotherm, Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Temperature programmed reduction (TPR), and Temperature-programmed desorption of ammonia (NH 3 -TPD). XRD, BET, and SEM data confirmed that the catalysts were mesoporous and low-crystalline with a high surface area. The soot oxidation activity of the catalysts was evaluated using a thermogravimetric analysis (TGA) technique. The loose contacts soot oxidation activity test suggested that 50% oxidation of soot occurred at 390 °C in the absence of a catalyst. T 50 of CeO 2 -Al 2 O 3 catalyzed soot oxidation was 296 °C. Adding Zr to the catalyst significantly improved catalytic activity for diesel soot oxidation. We observed a further drastic change in T 50 of soot over 1, 3, and 5% Zr/CeO 2 -Al 2 O 3 , which were 220 °C, 210 °C, and 193 °C, respectively. According to these results, incorporating Zr into the CeO 2 -Al 2 O 3 catalyst significantly improved the oxidation process of soot. Graphical Abstract

The design of modern aftertreatment systems to meet Real Driving Emissions (RDE) regulations is a significant challenge faced by manufacturers today. This is because testing vehicles under RDE conditions is both time consuming and expensive. In this study, we quantify the effect of real driving conditions on vehicle performance (efficiency and emissions) using a system model comprised of vehicle and aftertreatment subsystems, built using the commercial simulation software GT-SUITE. The developed system model will allow manufacturers to predict vehicle performance and prospective emissions under real driving conditions early in the development cycle and to ensure compliance with current and future regulations. The engine used in this study is a 2.0 L turbocharged diesel engine, while the aftertreatment system consists of a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), and a selective catalytic reduction (SCR). The simulated real driving route was generated by using a new feature that uses real-time global positioning system (GPS) data to calculate a driving route from a defined starting point to a destination. The feature considers current traffic conditions (traffic lights, traffic density, speed limits, etc.) and allows different driver profiles to be simulated. In this study, a city driving route in Los Angeles (LA) County and a highway driving route from New York City (NYC) to LA were simulated with average traffic light durations of 15 s and 90 s. In addition, two driver profiles were simulated for each route and traffic light duration. The effect of all these factors on the observed engine efficiency and emissions is quantified and discussed. The aftertreatment system features a high-fidelity DOC model that was developed based on synthetic gas bench (SGB) data from the literature with additional mechanisms for sulfur poisoning and platinum oxidation. The effects of sulfur poisoning, as well as platinum oxidation on DOC-out emissions, were also investigated under the real driving scenarios.

Hydrogen presents a promising opportunity for the reduction of CO 2 emissions in combustion processes. Due to its wide ignition limits, operation in lean mode is possible, which significantly reduces NO x emissions. However, this lean operation also leads to a reduction in the resulting torque. In contrast, stoichiometric operation increases maximum power output but leads to increased NO x emissions. In particular, a cost-effective three-way catalyst can be used in stoichiometric operation, enabling effective emission control. This investigation proposes an innovative approach that involves lean-burn operation at part load conditions and switching to stoichiometric operation at full load. The transition between these two modes has a considerable impact on overall NO x emissions. To optimize this process, new functions were developed that implement countermeasures such as lambda control, ignition timing adjustment, catalyst purging, and shortening the switching range through the use of variable valve timing and variable turbine geometry. The results show that nitrogen oxide (NO x ) emissions downstream of the three-way catalyst are kept below in the lean operating range and below in the stoichiometric operating range. By optimizing the transition between the two operating modes and using advanced emission control technologies, it is possible to reduce NO x emissions by 84% while maintaining power efficiency under different load conditions. In addition, the almost torque-neutral switching between the two operational modes ensures that the vehicle’s drivability is not impaired. By incorporating additional dosing of a urea-water solution in an active SCR system, a significant improvment in NO x reduction is attained, achieving levels comparable to those of diesel internal combustion engines. This dual-mode operation strategy improves the feasibility of hydrogen as a viable fuel alternative in future energy systems.

Worldwide emission standards are now required to cover engine operation under extreme ambient conditions, which affect the raw emissions and the efficiency of the exhaust aftertreatment systems. These regulations also target new combustion technologies for decarbonization, such as neat hydrogen (H2) combustion or dual-fuel strategies, which involve a challenge to the analysis of exhaust aftertreatment system requirements and performance. This work addresses the impact of high altitude and low ambient temperature conditions on the reactivity of an oxidation catalyst in the presence of H2. A reaction mechanism is proposed to cover the main conversion paths of CO, HC, and H2, including the formation and consumption of high-energy surface reaction intermediates. The mechanism has been implemented into a faster-than-real-time reduced-order model for multi-layer washcoat honeycomb catalytic converters. The model was utilized to investigate the effect of H2 concentration on the reactivity of CO and HC within the catalyst under various operating and ambient conditions. By applying the model and examining the selectivity towards different reaction pathways in the presence of H2, insights into surface intermediates and reactivity across different cross-sections of the monolith were obtained. This analysis discusses the underlying causes of reactivity changes promoted by H2 and its relative importance as a function of driving boundary conditions.

Emissions of marine traffic can be lowered by switching to less polluting fuels or by investing in exhaust aftertreatment. Electrostatic precipitation is a widely used method for particle removal but it is not currently used in combination with marine engines. This study presents the particle filtration characteristics of an emission reduction system designed for marine applications and consisting of a scrubber and a Wet Electrostatic Precipitator (WESP) in series. Partial flow of exhaust from a 1.6 MW marine engine, operated with light and heavy fuel oil, was led to the system. Particle concentrations were measured before the system, after the scrubber and after the WESP. Particle removal characteristics were determined for different engine loads. The scrubber alone removed 15–55% of non-volatile particle number, 30–40% of particle mass and 30–40% of black carbon mass depending on engine load, when HFO fuel was used. By studying particle size distributions, scrubber was found also to generate particles seen as an additional mode in 20–40 nm size range. The system combining the scrubber and WESP removed over 98.5% of particles in number, mass and black carbon metrics when HFO fuel was used. With MDO fuel, 96.5% of PN and 99% of black carbon were removed.

Hydrogen as carbon-free fuel is a very promising candidate for climate-neutral internal combustion engine operation. In comparison to other renewable fuels, hydrogen does obviously not produce CO2 emissions. In this work, two concepts of hydrogen internal combustion engines (H2-ICEs) are investigated experimentally. One approach is the modification of a state-of-the-art gasoline passenger car engine using hydrogen direct injection. It targets gasoline-like specific power output by mixture enrichment down to stoichiometric operation. Another approach is to use a heavy-duty diesel engine equipped with spark ignition and hydrogen port fuel injection. Here, a diesel-like indicated efficiency is targeted through constant lean-burn operation. The measurement results show that both approaches are applicable. For the gasoline engine-based concept, stoichiometric operation requires a three-way catalyst or a three-way NOX storage catalyst as the primary exhaust gas aftertreatment system. For the diesel engine-based concept, state-of-the-art selective catalytic reduction (SCR) catalysts can be used to reduce the NOx emissions, provided the engine calibration ensures sufficient exhaust gas temperature levels. In conclusion, while H2-ICEs present new challenges for the development of the exhaust gas aftertreatment systems, they are capable to realize zero-impact tailpipe emission operation.

Particle emissions from marine activities next to gaseous emissions have attracted increasing attention in recent years, whether in the form of black carbon for its contribution to global warming or as fine particulate matter posing a threat to human health. Coastal areas are particularly affected by this. Hence, there is a great need for shipping to explore alternative fuels that both reduce greenhouse gas emissions, as anticipated through IMO, and also have the potential to reduce particle emissions significantly. This paper presents a comparative study of the particulate emissions of two novel synthetic/biofuels (GTL and HVO), which might, in part, substitute traditionally used distillate liquid fuels (e.g., MDO). HFO particulate emissions, in combination with an EGCS, formed the baseline. The main emphasis was laid on particle concentration (PN) and particulate matter (PM) emissions, combining gravimetric and particle number measurements. Measurements were conducted on a 0.72 MW research engine at different loads (25%, 50%, and 75%). The results show that novel fuels produce slightly fewer emissions than diesel fuel. Results also exhibit a clear trend that particle formation decreases as engine load increases. The EGCS only moderately reduces particle emissions for all complaint fuels, which is related to the formation of very fine particles, especially at high engine loads.

Particulate Matter (PM) is one of the most sought-after exhaust emissions from Heavy-Duty Diesel Engines (HDDEs) to reduce. Several regulations in Europe and North America have led the way in drastically reducing PM of both on-road and off-road engines through stringent adoption of Diesel Particulate Filters (DPFs) and advanced combustion techniques. The effects of these advanced aftertreatment systems were studied using standardized testing procedures and equipment. While PM is defined as a “single” criteria pollutant, its complex structure entails several chemical compounds and molecules, displaying a whole spectrum of particle sizes. In addition, the morphology of some volatile compounds is shown to be affected by the interaction with background air during exhaust dilution and cooling. Although a variety of studies have attempted to fully capture dilution conditions taking place in the wake of a vehicle and reproduce those in a laboratory environment, a gap still exists in the understanding of the formation and maturation of diesel exhaust aerosols once the exhaust is emitted into the atmosphere. This work aims to contribute to bridging the gap by offering particle characterizations obtained by both artificial dilution and direct sampling from the exhaust plume developing in the wake of a vehicle in a wind tunnel. Three heavy-duty trucks were selected for this study representing three different states of engine technologies. Results suggest that laboratory techniques commonly used in diesel exhaust particle characterization work may not fully capture the evolution of PM particles once they leave the tailpipe. This appears to be especially true for particles in the nucleation mode size range in the case of vehicles equipped with DPFs.

Worldwide emission standards are extending their requirements to cover engine operation under extreme ambient conditions and fill the gap between the type-approval and real driving conditions. The new ambient boundaries affect the engine performance and raw emissions as well as the efficiency of the exhaust aftertreatment systems. This study evaluates the impact of high altitude and low ambient temperature on the light-off temperature and conversion efficiency of an oxidation catalyst. The results are compared in a common range of exhaust mass flow and temperature with the baseline sea-level operation at 20 °C. A reduction of CO and HC conversion efficiencies was found at 2500 m and −7 °C, with a relevant increase of the light-off temperature for both of the pollutants. The analysis of the experimental data was complemented with the use of a catalyst model to identify the causes leading to the deterioration of the CO and HC light-off. The use of the model allowed for identifying, for the same exhaust mass flow and temperature, the contributions to the variation of conversion efficiency caused by the change in engine-out emissions and tailpipe pressure, which are, in turn, manifested in the variation of the reactants partial pressure and dwell time as governing parameters.