Search Results (278)

This paper investigates nanoparticle emissions from older diesel passenger cars in four European countries outside of PTI (periodic technical inspection) testing facilities, using a methodology similar to that of the PTI. Per opportunistic sampling and voluntary testing, 618 diesel cars with an average mileage of 163,348 km were measured between 2020 and 2022 on the streets around university campuses and in public areas in Brussels (Belgium), Aveiro (Portugal), Belgrade (Serbia) and Birkenfeld (Germany). Through subsequent research, 109 vehicles were found not to be equipped with a diesel particulate filter (DPF) and were separated. Portable nanoparticle detectors were used to measure PN emissions in a PTI-like approach at low idle. From the 509 analysed diesel cars equipped with DPF, a high share of 31% revealed PN tailpipe concentrations of over 250 kP/cm³ and would therefore have failed the PTI established in Germany. That rate is 2–9 times higher than that found in Belgian and German PTI PN measurements, possibly caused by the fact that vehicles are serviced immediately before the PTI. Moreover, 45% of all tested diesel cars with DPF emitted concentrations higher than 20 kP/cm³. This level was found, both in the literature and in our measurements, to be indicative of a DPF operating outside its normal performance range, taking into account the measurement uncertainty. Even among relatively new vehicles with DPF (up to mileages of 180,000 km), 13% emitted as much PN as diesel cars without DPF (1000 kP/cm³ or more). In Portugal and Serbia, a higher share of cars showed elevated emissions compared to Germany and Belgium. DPF technology can in principle greatly reduce particle emissions of diesel cars. However, its efficiency degrades with time and vehicle mileage. Several factors leading to higher PN emissions have been reported; however, they cannot be discriminated in the results. This is primarily because active filter regeneration generates particle emission peaks every several 100 km, which were found to be up to four orders of magnitude higher than normal. Within the fleet on the streets, up to 4% of all diesel cars equipped with a modern DPF can be found in active regeneration mode. While at present politics and carmakers focus on electrifying the new vehicle generation, the emission problem of around 69 million diesel cars with elevated PN emissions on European streets remains unresolved so far. In European countries with a particularly high share of diesel cars, an old vehicle fleet, and a low income level, emission problems may be exacerbated. Full article

Heavy-duty methanol engines are regarded as a promising low-carbon solution for commercial vehicle decarbonization, yet the comprehensive coupled characteristics of fuel consumption, multi-dimensional exhaust emissions, and the corresponding aftertreatment adaptability between stoichiometric and lean-burn technical routes remain insufficiently quantified, restricting the optimized application of methanol powertrains for China-VI emission compliance. To address this research gap, this study systematically investigates two China-VI compliant heavy-duty methanol engines with stoichiometric and lean-burn combustion strategies under cold-start and hot-start Worldwide Harmonized Transient Cycle. And a comparative analysis is conducted to clarify the differences in the fuel consumption, raw exhaust emission (including regulated pollutants, particulate matters, greenhouse gases, and unregulated pollutants), and the catalytic performance of aftertreatment systems between two engines with stoichiometric and lean-burn strategy. Results demonstrate that the lean-burn strategy achieves a 6% reduction in methanol fuel consumption compared with stoichiometric combustion, delivering superior fuel economy. In terms of regulated gaseous pollutants, both combustion strategies satisfy China-VI emission limits for CO and NO, while lean-burn combustion effectively lowers raw CO and NO emissions and reduces the purification pressure of aftertreatment systems. Non-methane Hydrocarbon emission under cold-start condition is identified as the primary compliance challenge, requiring a minimum aftertreatment conversion efficiency of 95%. Although lean-burn increases raw exhaust NMHC emission under hot-start condition, the post-catalyst emission could still meet the regulation limits. For particulate pollutants, lean-burn strategy realizes substantial reductions in both PM and PN emissions, which can meet emission standards without the corresponding aftertreatment system. In contrast, the stoichiometric combustion faces a risk of PN emission exceeding the regulation limit under cold-start conditions even with aftertreatment system. Additionally, lean-burn strategy optimizes greenhouse gas emission performance by cutting CO and CH₄ emissions. Regarding unregulated pollutants, lean-burn strategy increases raw exhaust unburned methanol and formaldehyde emissions, particularly under cold-start condition, but significantly inhibits NH₃ emission. This study quantitatively clarifies the performance trade-offs and adaptation advantages of lean-burn and stoichiometric strategy for heavy-duty methanol engines, providing fundamental data support and technical guidance for the low-carbon and low-pollution optimization of heavy-duty methanol vehicles. Full article

Ammonia is increasingly regarded as a carbon-free energy carrier for hard-to-electrify power sectors, including marine propulsion, heavy-duty transport, and distributed generation. Its direct use in internal combustion engines, however, is constrained by high ignition energy, low laminar flame speed, narrow flammability limits, slow low-temperature chemistry, and strong trade-offs among efficiency, nitrogen-containing emissions, and unburned ammonia slip. Hydrogen enrichment is one of the most effective routes for improving ammonia combustion reactivity, but it also introduces a multivariable control problem: hydrogen fraction, ammonia injection timing, injection mode, air-path dilution, ignition strategy, and aftertreatment operation are tightly coupled and strongly condition-dependent. This review synthesizes recent progress in ammonia–hydrogen and ammonia-based dual-fuel engine control from a control-oriented perspective. The discussion first summarizes application scenarios, nonlinear combustion-mode transitions, emission-formation pathways, and control-relevant metrics. It then compares actuator-level strategies, including ammonia injection timing and staging, port and direct injection, hydrogen energy-fraction scheduling, excess-air-ratio and EGR control, high-energy ignition, and turbulent jet ignition. Advanced optimization methods are further reviewed, with emphasis on model predictive control, control-oriented combustion and emission models, artificial-intelligence-based virtual sensors, and reinforcement-learning control. The analysis shows that the central challenge is no longer whether ammonia can burn in an engine, but how a controller can keep the system inside a narrow moving window bounded by misfire, knock, NO_x, N₂O, and NH₃ slip. Finally, future research priorities are proposed, including engine–aftertreatment co-optimization, physics-informed virtual sensing, digital-twin-assisted calibration, lightweight deployment on electronic control units, and robust control under fuel and aging uncertainty. Full article

Diesel-powered equipment is widely used in underground coal mines for auxiliary transportation, material handling, and equipment relocation because of its long operating endurance, convenient refueling, and strong adaptability to complex operating conditions. However, carbon monoxide (CO) emissions from such equipment can accumulate locally under restricted ventilation, idling, and frequent start–stop operation, thereby threatening occupational health and mine safety. This review focuses on CO purification technologies for diesel-powered mining equipment. The operating characteristics and influencing factors are analyzed, and different technical routes are compared, including in-cylinder control, wet scrubbing, adsorption, non-thermal plasma (NTP), and catalytic oxidation. Recent advances in noble-metal catalysts, transition-metal and CeO₂-based reducible oxide catalysts, and single-atom catalyst (SAC) design strategies are summarized. Research progress in exhaust aftertreatment systems is also discussed. Overall, CO purification for diesel-powered mining equipment requires coordinated optimization of low-temperature activity, safety-oriented thermal management, flow resistance, and long-term operational stability. Future research should focus on structured catalytic units, durability under coupled exhaust conditions, online monitoring, and field validation to improve the compatibility of CO purification systems with underground mining conditions. Full article

Advanced biofuels represent a key option for transport decarbonization, particularly in sectors where electrification is constrained by technical and economic barriers. Their compatibility with existing vehicle fleets and fuel distribution infrastructure enables rapid deployment without the need for major capital investments. In local public transport, biodiesel (FAME), hydrotreated vegetable oil (HVO), and biomethane are mature solutions capable of delivering greenhouse gas emission reductions of 60–90% compared with fossil fuels. Among these, HVO is particularly promising, as an extensive body of literature has consistently shown its potential to significantly reduce engine-out emissions, especially particulate matter (PM) and nitrogen oxides (NO_x). This study reports the results of an experimental campaign carried out on a diesel-powered local public transport bus equipped with a Euro III engine and lacking particulate matter and NO_x after-treatment systems. Emissions were measured using a portable emissions measurement system (PEMS) under real driving conditions, operating the vehicle with neat diesel, a 15% HVO blend, and a 70% HVO blend. Tests were conducted over urban and extra-urban routes. The results show that NO_x emissions decrease proportionally with increasing HVO content, with high-blend ratios (HVO70) yielding estimated reductions of approximately 13–18%, and up to 23% under carefully controlled and comparable urban driving conditions. Based on these findings and the existing literature, HVO proves to be a useful instrument to meet 2025–2030 climate and air quality targets (particularly NO_x and PM emission reductions), alongside electrification and modal shift measures, if used in public transport fleets. Full article

Electrocatalytic nitric oxide reduction (NORR) shows great potential for mitigating NO_x emissions from motor vehicles and other internal combustion engine exhausts, enabling the resource utilization of pollutant NO and the synthesis of NH₃ under mild conditions. The overall performance of NORR largely depends on the development of efficient electrocatalysts. Based on a coordination-engineering strategy, this study constructs a series of Sc-based single-atom catalyst systems coordinated with nonmetal heteroatoms (X = B, C, O, Si, P, S, As, Se, Te), denoted as Sc@XN₃, and systematically investigates their NORR reaction pathways, limiting potentials (U_L, the minimum applied potential required to make all elementary steps downhill in free energy), and selectivity using density functional theory (DFT) calculations. The results indicate that Sc@CN₃, Sc@PN₃, and Sc@SN₃ possess relatively low U_L, with values of −0.17, −0.31, and −0.07 V, respectively, among which Sc@SN₃ is thermodynamically the most favorable. Moreover, Sc@CN₃ and Sc@SN₃ can suppress the hydrogen evolution reaction (HER) and the formation of N₂O/N₂ by-products, thereby affording higher selectivity toward NH₃ formation. Considering the characteristics of NO_x emissions from engine exhaust, these coordination-engineered Sc centers show promising potential for future electrified aftertreatment systems that couple NO_x control with ammonia-based energy utilization in vehicles. This study clarifies at the atomic scale how the coordination environment modulates the electronic structure and catalytic behavior of Sc single-atom centers and provides theoretical guidance for the rational design of high-performance NORR electrocatalysts targeted at automotive exhaust NO_x control. Full article

Marine diesel engines generate high concentrations of sub-micron particulate matter (PM) that requires effective exhaust aftertreatment. While conventional wire-in-tube electrostatic precipitators (ESP) offer a low-drag solution, their practical efficiency is limited by particle re-entrainment at elevated flow velocities. This study investigates a novel application of corrugated cylindrical ducts—standard vibration-compensating couplings—as electrostatic collectors. A fully coupled two-dimensional axisymmetric COMSOL Multiphysics 6.4 model was developed, integrating turbulent flow (k–ε), electrostatics, ion charge transport, and particle tracing. Numerical results demonstrate that while smooth and corrugated geometries yield identical theoretical Deutsch–Anderson efficiency (61.1% at Uin = 0.5 m/s, the corrugated profile significantly suppresses re-entrainment. The corrugations reduce wall shear stress by a factor of 7.7 to 13.5 at flow velocities of 0.3–0.8 m/s, maintaining aerodynamic conditions below critical particle detachment thresholds. With a pressure drop penalty representing less than 6% of the localized corona power, these findings show that existing marine exhaust infrastructure can be repurposed as high-efficiency, low-re-entrainment particle collectors through the integration of cold plasma electrodes. Full article

Ammonia, as a carbonless carrier of energy, presents considerable potential for hydrogen storage and production, as well as for power generation, thanks to its high energy density and relatively easy transportability. However, the practical adoption of ammonia in combustion systems faces major stability challenges—chiefly its low reactivity, slow laminar burning velocity, narrow flammability envelope, and high ignition temperature. These attributes increase the risks of flame instability, misfire, and incomplete combustion, which, in turn, can elevate levels of unburned ammonia and greenhouse gas emissions such as NOx—posing significant health and climate concerns. Stable ammonia combustion demands optimization of several interrelated factors: the air–fuel equivalence ratio, flame temperature, flow regime, and combustor design are critical for maintaining reliable operation. Particularly pivotal is the control of the air–fuel equivalence ratio; excessively lean conditions can trigger flameout. Modern systems utilize real-time monitoring of flame and exhaust properties to diagnose and prevent instabilities. Advanced combustion strategies, such as transitioning to diffusion or flameless (MILD) regimes, substantially expand the stable operating window, especially under lean conditions. Overall, sustaining stable ammonia combustion is essential for maximizing efficiency and emission control, and integrating aftertreatment (deNOx) technologies is crucial for sustainable, clean-energy implementation. Full article

The transition to a hydrogen-based energy economy emphasizes the potential of hydrogen as a fuel for plug-in hybrid electric vehicles (PHEVs). The performance of a hydrogen engine within a PHEV depends on the choice of its operating modes, which influence both efficiency and emissions. This study proposes a method for developing engine operating lines (EOLs) on engine maps based on minimizing nitrogen oxide (NOx) emissions while considering constraints on maximum engine power. A total of 15 EOLs are proposed for configurations with both constant and variable maximum engine power. Using mathematical modeling of PHEV operation under the Worldwide Harmonized Light Vehicles Test Cycle (WLTC), the impact of EOL selection on engine characteristics, as well as on battery and generator parameters, is analyzed. For a comprehensive evaluation of EOL effectiveness, five criteria are introduced, considering fuel energy consumption, NOx emissions, wear, mechanical fatigue, and noise, vibration, and harshness (NVH). The Analytic Hierarchy Process (AHP) and the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) are applied to determine the weighting factors of the criteria and to rank the proposed EOLs, thereby identifying the most efficient configurations. The results show that, for the base hydrogen engine configuration, selecting appropriate operating modes alone enables NOx emissions to be reduced significantly below Euro 6 limits, without any hardware modifications or exhaust aftertreatment. Full article

To promote the green and low-carbon transition and achieve sustainable development in the transportation sector, virtual calibration technology was employed for the efficient and precise control of emissions from heavy-duty diesel engines and aftertreatment systems. A data-driven, semi-empirical and semi-physical simulation modeling method was proposed. By constructing core modules based on physical mechanisms and refining empirical parameters using experimental data, the method improves computational efficiency while maintaining the prediction accuracy of key parameters. Additionally, a collaborative architecture combining physical actuators and virtual sensor signals was introduced, laying the foundation for the validity of virtual calibration. By innovatively introducing a closed-loop system with real actuators and virtual sensors, the dynamic response characteristics of the control system are faithfully reproduced, providing a reliable environment for validating the results of virtual calibration. Under steady-state conditions, the results demonstrated an average relative error of 1.7% for brake-specific fuel consumption (BSFC) and 6.1% for NOx emissions. An open-loop system for the virtual calibration testing platform was constructed for steady-state calibration. Using the main injection timing and common rail pressure as independent variables, a D-optimal design was utilized to generate 43 sets of experimental points, from which a polynomial regression model was established (R² ≥ 98%). Under the constraints of NOx and pre-turbine temperature, fuel consumption in the low-load range is reduced by 0.5–3 g/kW·h, aftertreatment NOx emissions are reduced by 0.5–3 g/kW·h, and exhaust temperature is increased by 10 °C. This study establishes a complete development workflow consisting of “operating condition design-virtual optimization-bench validation,” significantly enhancing calibration efficiency and engineering applicability. This method shortens the calibration cycle and reduces the number of physical bench tests, providing the industry with a comprehensive calibration methodology tailored to engine operating conditions that is both reproducible and scalable. Full article

The emission of hydrogen cyanide (HCN) from formaldehyde (CH₂O) during ammonia-assisted selective catalytic reduction (NH₃-SCR) remains a critical challenge for aftertreatment of bio-hybrid fuel combustion exhaust. The mechanistic details of HCN formation are still poorly understood, especially on widely deployed commercial catalysts like Cu-SSZ-13. In this work, we employed density functional theory calculations in combination with the Energetic Span Model to elucidate HCN formation pathways from CH₂O in the presence of NO₂ and H₂O over Cu-SSZ-13. The results revealed the HCN formation pathway with intermediate methylene imine as the dominant one under typical reaction conditions. These findings resonate very well with reports of hexamethylenetetramine (HMT) formation during NH₃-SCR with CH₂O, for which methylene imine is a critical intermediate. Turnover frequency (TOF) estimations highlighted the strong influence of NO₂ and H₂O: higher NO₂ concentrations promoted CO selectivity and suppressed HCN by oxidizing CH₂O to HCOOH, while lower H₂O enhanced HCN formation. These findings establish a detailed mechanistic framework for HCN emission on Cu-SSZ-13 and suggest that controlling NO₂/NO_x ratios and water content can mitigate HCN formation during NH₃-SCR. Full article

This study investigates the synergistic promotional effects of CeO₂ and La₂O₂SO₄ as composite catalytic oxygen storage systems for soot oxidation in Gasoline Particulate Filters (GPFs) across a broad operating temperature range. Two 5 wt % CeO₂-promoted Lanthanum oxysulfate compounds were prepared by mechanical mixing of pure phases or by supporting CeO₂ via incipient wetness impregnation with a cerium nitrate precursor. The soot oxidation activity was evaluated using Thermogravimetric Analysis coupled with Mass Spectrometry (TG-MS) under both anaerobic and lean-O₂ (1% vol.) environments, with the performance benchmarked against pure La- or Pr-oxysulfates and CeO₂ reference materials. Comprehensive characterization via XRD, SEM, N₂-physisorption, and H₂-TPR revealed that the observed synergistic effects transcend the simple additive properties of the individual components. Full article

Aviation heavy-fuel piston engines are widely used in UAVs, general aviation, and military platforms due to their fuel efficiency and adaptability. However, emissions of NO_x, PM, and other pollutants pose significant environmental challenges. This paper reviews emission-reduction strategies, including combustion-chamber optimization, fuel-injection control, alternative fuels, and exhaust after-treatment technologies. Research indicates that optimizing combustion-chamber geometry, high-pressure common-rail injection, and turbulence enhancement improve combustion efficiency and reduce emissions. Biofuels, synthetic aviation fuels (SAF), and hydrogen-based fuels demonstrate strong potential for low-carbon emissions, while after-treatment technologies such as SCR, DPF, and EGR effectively mitigate NO_x and PM emissions. Despite technological advancements, challenges remain in balancing combustion efficiency with NO_x control and ensuring compatibility between EGR and combustion stability. Future advancements in intelligent combustion control, novel catalytic materials, low-temperature combustion, and high-efficiency after-treatment systems will drive aviation diesel engines toward lower emissions, higher efficiency, and greater intelligence, contributing to the green and sustainable transformation of aviation propulsion systems. Full article

DOC coupled with SCR represents a key technological approach for reducing gaseous pollutant emissions from diesel engines. Based on engine bench testing using a light-duty diesel engine as a prototype, this study investigates the impact of DOC coupled with SCR at different catalyst loadings on diesel engine emission characteristics. Results indicate that higher DOC loadings lead to greater exhaust backpressure losses, with a maximum pressure difference reaching 4.3 kPa. The temperature difference across the DOC was minimally affected by catalyst loading. Higher DOC loading enhanced catalytic activity toward CO and THC. At medium-to-low loads, this effect was pronounced, while at high loads, the influence of catalyst loading diminished. Higher DOC loading enhances NO oxidation capacity. Under external characteristic conditions, elevated engine exhaust temperatures maximize post-DOC NO₂ formation, increasing post-DOC NO₂ production by over 100%. These findings provide useful guidance for optimizing diesel aftertreatment systems to achieve a better balance between pollutant reduction, energy consumption, and environmental sustainability, thereby supporting the sustainable development of cleaner diesel engine technologies. Full article

Exhaust after-treatment (EAT) thermal management remains a critical challenge for diesel engines operating under low-load conditions, where low exhaust temperatures delay catalyst light-off and reduce emission control efficiency. This operating regime is common in marine auxiliary engines and onboard diesel generator sets during hoteling, maneuvering, and partial-electrical-load conditions. Conventional strategies such as late fuel injection or exhaust throttling can increase exhaust temperature but often result in significant fuel consumption penalties. This study numerically investigates the combined use of late exhaust valve opening (LEVO) and cylinder deactivation (CDA) to enhance EAT thermal management with a reduced fuel penalty. A six-cylinder diesel engine is analyzed at a low-load condition (1200 RPM, 2.5 bar BMEP) using a calibrated one-dimensional engine simulation model. LEVO applied to all cylinders increases exhaust temperature to approximately 250 °C, but with a considerable increase in fuel consumption. When two cylinders are deactivated and the remaining cylinders operate with LEVO, airflow and pumping losses decrease, enabling higher exhaust temperatures at comparable fuel consumption levels. Despite a 30% reduction in exhaust mass flow rate, the higher exhaust temperature dominates EAT heat transfer. Consequently, the combined strategy increases EAT heat transfer by up to 143% and achieves exhaust temperatures approaching 295 °C. These results indicate that combined valve timing and load redistribution through CDA can improve the exhaust temperature–mass flow trade-off, providing a potential pathway for enhanced EAT warm-up during low-load operation within the limitations of the numerical model. Full article