Lean NOx Trap Research Articles

Experimental Investigation on Compact Current Non Thermal Plasma Assisted Hydrocarbon Reforming Hydrogen Rich Gas

On-board vehicle hydrogen-rich gas extraction of gasoline reforming utilizing for fuel cells and GDI-engine lean burn combustion enhancement NOx trap applications. A non-thermal plasma discharge electrode that produces a reduce current, increased voltage 15kV source arc plasma fuel reformer is designed to operate at an arc frequency of 50 Hz. The operating factors gasoline equivalence ratio between 4 and 6.and electronically control by the fuel injector and eliminating ground spark plug plasma arc generation. The plasma arc non-thermal reformer gasoline converted into gas that contains partial oxidation contains combustible gases like hydrogen (H2), CO, non-combustible gases like CO2, N2, and a small quantity of H2O. The nonthermal plasma technology alternative for on-board hydrogen vehicle applications.

A novel Pd-doped perovskite-based LaCo0·9Pd0·1O3–Ba/Al2O3 catalyst enhances NOx to ammonia reaction

The effect of Pd doping on the NOx removal efficiency and NH3 selectivity was studied over lean NOx trap LaCo1-xPdxO3-Ba/Al2O3-type catalysts. Two catalysts were prepared by the sequential impregnation of 15 wt% of LaCo1-xPdxO3-type perovskites and 20 wt% of barium over alumina. The results of X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, temperature programmed techniques, UV–vis diffuse reflection absorption spectroscopy, and X-ray photoelectron spectroscopy demonstrated that perovskite and barium grains uniformly distribution over the alumina surface. Cobalt partial substitution by palladium changed the chemical coordination environment, thus leading to the redox properties of perovskites getting different. Moreover, the LaCoO3–Ba/Al2O3 catalyst exhibited a high reduction on NOx by H2 between 450 and 550 °C. Whereas Pd-doped LaCo0·9Pd0·1O3–Ba/Al2O3 catalyst decreased the best activity interval around 100 °C, as well as improved the NH3 selectivity. The NOx reduction conversion of the LaCo0·9Pd0·1O3–Ba/Al2O3 catalyst increased significantly from 72.9% to around 100% at H2/NO ratio = 1, and the production of NH3 was increased from 20.1% to 58.6% at H2/NO ratio = 3.

Pt–Cu dual-site synergistic construction in lean NOx traps(LNTs)towards high NH3 selectivity

The traditional NH3-SCR technology has some drawbacks since it requires an additional NH3 source; nevertheless, the LNT-SCR coupling system could efficiently use the byproduct (NH3) of the lean NOx traps (LNTs) as a NH3 source for the NH3-SCR catalyst to reduce NOx. Therefore, the regulation of NH3 selectivity in LNT to enhance NOx removal efficiency in LNT-SCR coupling system have been a prominent focus of research. As previously discovered, the LNT catalyst Cu(5)/Ba(5)/CeO2 demonstrated high NOx storage efficiency with low NOx removal and NH3 slip efficiencies; however, the Pt(1)/ZrO2 catalyst exhibited low NOx storage efficiency and high NH3 slip efficiency. In this study, a Pt–Cu dual-site LNT catalyst was prepared using the high-energy ball milling method with the aim of ensuring that the Cu and Pt sites can perform their respective roles in enhancing NOx removal efficiency and NH3 selectivity. The Pt(1)/ZrO2+Cu(5)/Ba(5)/CeO2 exhibited NOx storage and removal efficiencies of 98.8 % and 92.1 %, respectively, as well as the NH3 slip efficiency of 83.6 %. A comprehensive characterization was also conducted to analyze the effects of co-impregnation and high-energy ball milling methods on a Pt–Cu dual-site LNT catalyst. XPS, CO-DRIFTs, and HRTEM-EDS results demonstrated that the Pt and Cu in Pt(1)/ZrO2+Cu(5)/Ba(5)/CeO2 were less influenced compared to Pt(1)/Cu(5)/Ba(5)CeO2–ZrO2, resulting in relatively independent and aggregated reaction sites favoring the Pt and Cu sites in their respective roles and generating high concentrations of Ce3+ species and surface oxygen, which facilitated effective NOx storage. The exceptional NH3-generation capability displayed by the Pt(1)/ZrO2+Cu(5)/Ba(5)/CeO2 holds significant promise for NOx purification in the LNT-SCR coupling system.

Thermally Induced Structure and Functionality Evolution of a Pt‐based Lean NOx Trap Catalyst

Applying a NOx trap catalyst to effectively remove NOx contaminants from the oxygen‐rich exhaust is still very challenging, due to the lack of use guidance based on deactivation mechanisms. The temperature‐dependent Pt sintering rate constant was described using Pt dispersion determined by pulse CO chemisorption. It was found that 700‐850 ºC was the determining temperature regions for the significant Pt sintering, according to the sintering kinetics and the evolution of active Ptδ+ sites. The weak basicity plays a critical role in trapping NOx at low‐temperature (≤ 300 ºC), and the NOx trap efficiency decreases because of the loss of catalytic activity and medium basicity caused by forming BaAl2O4 phase. The reduction of NOx towards N2 on the Pt crystallites smaller than 18 nm is structure sensitive and decreases with losing the reducibility of catalysts. The security for long‐time use of a NOx trap catalyst should be exposed to the exhaust gas within 750 ºC, and effectively removing NOx contaminants requires it to be worked in the 350‐500 ºC regions. These findings can guide engineers and applied chemists how to efficiently use a NOx trap catalyst in the automotive exhaust purification system.

Catalytic NO<sub>x</sub> Aftertreatment—Towards Ultra-Low NO<sub>x</sub> Mobility

Article Catalytic NOx Aftertreatment—Towards Ultra-Low NOx Mobility Navjot Sandhu * , Xiao Yu, and Ming Zheng Department of Mechanical, Automotive and Materials Engineering, University of Windsor, 401 Sunset Avenue, Windsor, ON N9B 3P4, Canada * Correspondence: sandh12p@uwindsor.ca Received: 26 January 2024 Accepted: 13 March 2024 Published: 20 March 2024 Abstract: The push for environmental protection and sustainability has led to strict emission regulations for automotive manufacturers as evident in EURO VII and EPA2027 requirements. The challenge lies in maintaining fuel efficiency and simultaneously reducing the carbon footprint while meeting future emission regulations. Nitrogen oxides represent one of the major and most regulated components of automotive emissions. The need to meet the stringent requirements regarding NOx emissions in both SI and CI engines has led to the development of a range of in-cylinder strategies and after-treatment techniques. In-cylinder NOx control strategies including charge dilution (fresh air and EGR), low-temperature combustion, and use of alternative fuels (as drop-in replacements or dual fuel operation) have proven to be highly effective in thermal NOx abatement. Aftertreatment methods are required to further reduce NOx emissions. Current catalytic aftertreatment systems for NOx mitigation in SI and CI engines include the three-way catalyst (TWC), selective catalytic reduction (SCR) and lean NOx trap (LNT). This review summarizes various approaches to NOx abatement in IC engines using aftertreatment catalysts. The mechanism, composition, operation parameters and recent advances in each after-treatment system are discussed in detail. The challenges to the current after-treatment scenario, such as cold start light off, catalyst poisoning and the limits of current aftertreatment solutions in relevance to the EURO VII and 2026 EPA requirements are highlighted. Lastly, recommendations are made for future aftertreatment systems to achieve ultra-low NOx emissions.

Green ammonia synthesis from stationary NOx emission sources on a catalytic lean NOx trap

The NOCCRA (NOx capture and catalytic reduction to ammonia) process enables local ammonia/fertiliser production out of NOx in the flue gas of stationary engines. The two-phase process adsorbs NOx on a lean NOx trap, followed by reduction to NH3 by H2.

Lean NOx trap catalyst formulation for selective ammonia synthesis from captured NOx

In the Lean NOx Trap (LNT) technology, ammonia (NH3) occurs as reaction intermediate in conversion of trapped nitrogen oxides (NOx) to nitrogen gas (N2) using hydrogen gas (H2) reductant. The use of an LNT for synthesizing NH3 from NOx is potentially an attractive option for small-scale green NH3 production by converting locally produced NOx pollutant to an important chemical. In this work, it is investigated to what extent the product selectivity towards NH3 on the standard model catalyst Pt/BaO/Al2O3 can be maximized depending on reaction conditions for trapping and reducing NOx with H2 in the temperature range of 75–200 °C. The LNT catalyst preparation was varied by using Pt, Pd and bimetallic combinations, as well as different support materials, namely Al2O3, TiO2, ZrO2 and MgO. NOx adsorption and selectivity of captured NOx reduction to ammonia is discussed in terms of texture and the chemical nature of the support. The NH3 selectivity is influenced by the water vapor content in the gas feed. Storage of NOx in absence of water followed by reduction with hydrogen gas in presence of water vapor was found to be the most favorable operation mode of the LNT for NH3 formation. The NH3 selectivity reached 82% at 150 °C. Explanations for the role of water and in this catalytic chemistry are offered and its consequences for catalyst preparation are discussed. The optimum water content of the reacting gases is predicted to be strongly dependent on catalyst preparation.

Advancements in low-temperature NH3-SCR of NOx using Ba-based catalysts: a critical review of preparation, mechanisms, and challenges.

Presently, selective catalytic reduction (SCR), with either carbon monoxide, urea, hydrocarbons, hydrogen, or ammonia as a reductant, has become a nitrogen oxide (NOx) removal technology (NOx conversion) of many catalytic companies and diesel engine exhaust gas. Although, there exists a serious threat of low-temperature limitations. So far, certain scientists have shown that barium-based (Ba-based) catalysts have the potential to be highly effective at SCR of NOx at low temperatures when ammonia is used as the reducing agent. The process of NOx storage and reduction which alternate SCR is known as the Lean NOx trap. Herein, we give the condensed advancements and production of the catalysts that involve BaO in low-temperature NH3-SCR of NOx, the advantages of BaO catalysts compared to the recently hot electrocatalysis, the stability of BaO catalyst materials, and the condensed advancements and production of the catalysts that involve BaO in low-temperature NH3-SCR of NOx. These catalysts are viewed in the light of their preparation method, particulate, and posture in mixed oxides. Also, the characteristic features of Ba-based catalysts are carefully considered and briefed under the following areas: preparation method and precursor, crystallinity, calcination temperature, morphology, acid sites, the specific surface area for reaction, redox property, and activation energy of catalysts. More to these are the discussions on Eley-Rideal [E-R] and Langmuir-Hinshelwood [L-H] mechanisms, the H2O/SO2 and O2 permissiveness, and the NH3-SCR reaction mechanism over Ba-based catalysts highlighting their possible effects. Finally, we proposed the prospect and the likely future research plan for the low-temperature NH3-SCR of NOx.

Theoretical study on the migration of NOx to the Pt in proximity of Ba on γ-Al2O3(100)

Based on density functional theory (DFT) calculations, NOx tends to migrate from Ba to Pt sites within the Lean NOx trap (LNT), rather than reacting at Pt sites before migrating to Ba sites for storage as traditionally believed. Compared with NO and N2O, NO2 has the highest migration energy barrier, and there is a good linear relationship between the adsorption energy of NOx and its migration energy barrier. Furthermore, the essential cause of the above phenomenon is revealed. This study contributes to the exchange of NOx between noble metal catalytic sites and alkaline earth metal storage sites within the LNT.

Investigating the adsorption behavior of NOx molecules on γ-Al2O3(1 0 0)-supported proximal Pt-Ba clusters using density functional theory

The advancement of low to zero carbon fuels for internal combustion engines has made Nitrogen oxides (NOx) emissions a focal point of engine aftertreatment. Lean NOx Trap (LNT) is one of the most promising technologies for reducing NOx emissions in light-duty vehicles. The proximity of barium (Ba) to platinum (Pt) sites plays a significant role in the adsorption, reduction, and desorption of NOx inside LNT. A simultaneous loading of Pt clusters (Pt3) and barium oxide clusters ((BaO)2) on γ-Al2O3(100) was innovatively established in this study, and the effect of oxide carrier - triatomic catalyst clusters - bimolecular alkaline earth metal oxide clusters was considered comprehensively to examine the effect of Pt-Ba proximity on the NOx adsorption behavior. Interesting trends in the adsorption energy and activation of NOx molecules (including NO/NO2 and the strong greenhouse gas N2O) due to differences in the adsorption sites (from Pt sites to Pt-Ba proximity sites and finally to Ba sites) were found, and the essential reasons for such variations were elucidated by an exhaustive electronic structure analysis. The results of this study are an interesting complement to the current mechanism for storage and reduction of NOx.

Enhanced low-temperature NOx storage and reduction performance using Cu-loaded lean NOx trap catalysts

Lean NOx trap (LNT) used in diesel-powered vehicles exhibit poor NOx storage and reduction (NSR) performance during low-temperature operation, particularly under cold-start conditions. To overcome this limitation, Cu was added to a conventional LNT catalyst (Pt-Ba/γ-Al2O3, PBA) to improve the NOx storage and regeneration performance of the Cu-loaded Ba adsorbent (Cu-Ba/γ-Al2O3) during low-temperature operation. However, a Pt-Cu complex was formed when Pt and Cu were used together as a one-body catalyst (Pt-Cu-Ba/γ-Al2O3, PCBA), leading to decreased catalytic performance. Physical mixing was investigated as a method to prevent the catalytic performance degradation caused by the Pt-Cu complex. The physical mixture of Pt/γ-Al2O3 and Cu-Ba/γ-Al2O3 (PA + CBA) could prevent the formation of Pt-Cu complex and yielded the highest NSR performance at 150 ℃ among the synthesized LNT catalysts. PA + CBA maintained a significantly improved NSR performance in lean-rich cycling tests using CO or H2 as a reducing agent.

Emissions of currently non-regulated gaseous pollutants from modern passenger cars

The current vehicle type approval regulation in Europe controls specific exhaust gas constituents, while additional species may prove harmful for the environment and human health. This paper presents emission results of currently non-regulated gaseous pollutants from passenger cars. To this aim, four cars of different powertrain and exhaust aftertreatment technologies have been tested in a wide range of conditions. Ammonia (NH3), nitrous oxide (N2O) and methane (CH4) were included in the measurements, together with the currently regulated gaseous pollutants. The results showed that NH3 forms in the three-way catalyst (TWC) in harsh accelerations, while CH4 is the main hydrocarbon emitted by natural gas and diesel vehicles, the latter equipped with lean NOx trap. In spark-ignition engines, N2O formation was observed during the warm-up period of the TWC.

Study on Model-Based Development for Lean NOx Trap (Second Report)

Study on Model-Based Development for Lean NOx Trap (Second Report)

Optimizing model parameters of artificial neural networks to predict vehicle emissions

This paper presents a novel approach to predict carbon dioxide (CO2), nitrogen oxides (NOx), and carbon monoxide (CO) emissions of diesel vehicles using artificial neural network (ANN), which offer high degrees of accuracy and practicality. Six operating parameters (velocity, engine speed, engine torque, engine coolant temperature, fuel/air ratio, and intake air mass flow) collected through on-board diagnostic interface were used as predictors of exhaust emissions. The importance of each parameter to the emission predictions were comprehensively analyzed by comparing the coefficient of determination, root mean square error, cumulative emissions, and instantaneous emission rates. The emission prediction accuracy of ANN tends to increase as more parameters were considered as model inputs at the same time. However, the level of accuracy improvement depends on the input parameters. For CO2 emissions, engine torque and fuel/air ratio were good predictors for achieving high prediction accuracy. The relative importance of intake air mass flow rate and fuel/air ratio was high for NOx and CO predictions, respectively. In addition, the emission prediction accuracy of ANN depends on the vehicle type (Euro 5, Euro 6b, Euro 6d-temp). The emission prediction accuracy of vehicles equipped with after-treatment devices (selective catalytic reduction and lean NOx trap) was lower than that of vehicles without after-treatment devices.

Effects of substituting iron for aluminum on the low-temperature catalytic activity and sulfur resistance of hydrotalcite-derived LNT catalysts.

The storage and reduction of NOx on a series of Fe-modified hydrotalcite-based lean NOx trap catalysts were assessed, together with the product selectivity. The crystal structures and micromorphologies of these materials were characterized using X-ray diffraction and scanning electron microscopy, while in situ diffuse reflectance Fourier transform infrared spectroscopy was used to evaluate the evolution of transition state species. The introduction of Fe was found to improve the synergistic interaction between the Mg and Fe in the hydrotalcite structure, allowing these catalysts to work efficiently at low temperatures. In addition, both Pt/BaO/MgAlO and Pt/BaO/MgFeO catalysts exhibited better NOx adsorption and reduction performance compared with Pt/BaO/Al2O3. The superior performance of the former two materials was attributed to the enhanced adsorption of NOx in the form of nitrates and nitrites by Fe and Mg and to the ready decomposition of these nitrates at low temperatures. A Pt/BaO/MgFeO catalyst showed excellent low temperature activity and high selectivity for N2 together with superior sulfur resistance compared with Pt/BaO/Al2O3.

Contributions of Washcoat Components in Different Configurations to the NOX and Oxygen Storage Performance of LNT Catalysts

In addition to SCR systems, lean NOX traps (LNTs) are also used for exhaust aftertreatment of lean burn internal combustion engines to sustainably reduce NOX emissions. Modern LNTs consist of different functional compounds to maximize the performance during NOX storage and regeneration. Based on the material analysis of a serial production LNT, PGM loaded BaO, Al2O3, MgAl2O4, and CeO2 were identified as the main base materials. In this paper, the NOX storage capacity (NSC) of these compounds is investigated both as single catalysts and as physical mixtures to identify possible synergistic effects. Therefore, commercially available support materials were loaded with Platinum and tested in granular form under realistic conditions. To optimize the performance by reducing the diffusion pathways for NOX molecules during storage, PGM, BaO, and Ceria were combined in a composite by the incipient wetness impregnation of alumina. As a result, the temperature dependent NSC of the commercial LNT could be reached with the Pt/Rh/Ba10Ce25/Al2O3 infiltration composite, while reducing the oxygen storage capacity by about 45%. Without the additional Rhodium coating, the low-temperature NSC was insufficient, highlighting the important contribution of this precious metal to the overall performance of LNTs.

Impact of Active Diesel Particulate Filter Regeneration on Carbon Dioxide, Nitrogen Oxides and Particle Number Emissions from Euro 5 and 6 Vehicles under Laboratory Testing and Real-World Driving

Particulate mass concentration is a crucial parameter for characterising air quality. The diesel particulate filter (DPF) is the primary technology used to limit vehicle particle emissions, but it needs periodic cleaning, a process called regeneration. This study aims to assess the impact of active DPF regeneration on the performance and emissions of Euro 5 and 6 vehicles. The study examined both carbon dioxide (CO2) and pollutant (nitrogen oxides (NOx) and particle number (PN)) emissions for eight vehicles tested in the laboratory and on the road. Apart from the DPF, a wide range of emission control systems was covered in this experimental campaign, including exhaust gas recirculation (EGR), diesel oxidation catalyst (DOC), lean NOx trap (LNT) and selective catalytic reduction (SCR) catalyst, revealing the different impacts on NOx emissions. The regeneration frequency and duration were also determined and used to calculate the Ki factor, which accounts for the emissions with and without regeneration, weighted over the distance driven between two consecutive regeneration events. Based on these outcomes, representative emission factors (EF) were proposed for the regeneration phase only and the complete regeneration interval. In addition, the effect of regeneration on efficiency was estimated and compared with other energy consumers. The results indicated a significant impact of DPF regeneration on CO2, NOx and PN emissions, higher in the case of driving cycle testing in the laboratory. The relevant mechanisms behind the elevated emission levels were analysed, focusing on the regeneration period and the test phase following immediately after. The calculation of the Ki factor and the comparison with the official values revealed some weaknesses in its application in real-world conditions; to overcome these, new NOx EF values were calculated, depending on the emission control system. It was revealed that Euro 6 vehicles equipped with SCR could comply with the applicable limits when considering the complete regeneration interval. Finally, it was indicated that the DPF regeneration impact on vehicle efficiency is similar to that of driving with the air conditioning (A/C) system and headlights on.

NOx and Hydrocarbon Trapping and Conversion in a Sequential Three-Zone Monolith: Spatiotemporal Features

The spatiotemporal features of the multifunctional monolithic lean hydrocarbon NOx trap (LHCNT), for eliminating NOx (x = 1 and 2) and ethylene (C2H4), are examined using spatially resolved mass spectrometry (SpaciMS), spanning the sequentially positioned passive NOx adsorber (PNA; Pd/SSZ-13), hydrocarbon trap (HCT; Pd/BEA), and oxidation catalyst (OC; Pt/Al2O3–CeO2). The overall LHCNT performance is captured in temporal trapping efficiency profiles, which show the integral NO and C2H4 uptake followed by delayed NO release along with NO and ethylene oxidation. Spatially resolved transient concentration profiles spanning uptake, release, and conversion of NO, H2, and C2H4, alone or as mixtures in feeds containing H2O, provide detailed insight into the transient coupling not attainable with effluent concentration monitoring alone. The PNA serves as the primary zone for NO uptake, followed by the OC and HCT. NO oxidation to NO2 occurs during NO uptake in the PNA due to Pd(II) reduction, while more extensive oxidation occurs in the OC at higher temperature. C2H4 uptake and oxidation occur in each of the functions with oxidation occurring the earliest (lowest temperature) in the OC. NO uptake in the PNA and HCT is negligibly affected by H2 but protracted oxidation of H2 during the temperature ramp delays NO release, suggesting persistence of NO bound on Pd(I). Both the PNA and HCT exhibit excellent C2H4 uptake, which diminishes in the presence of NO. Spatially resolved concentration data reveal several interesting features, such as high-temperature, sequential NO oxidation (by O2 to NO2) and C2H4 oxidation (by NO2 to NO + CO2) in the PNA. Simulated warmup experiments reveal that the LHCNT NO trapping is enhanced with C2H4 addition but that a reduction in space velocity may be needed to improve performance. A previously developed PNA model predicts satisfactorily the main features of spatially resolved NO and NO + C2H4 data.

K2CO3/Al2O3 Composite Pellet as Room-Temperature NO2 Sensor

K₂CO₃, an alkaline carbonate, is commonly used as lean NOx trap device at elevated temperatures. In this device, K₂CO₃ along with some appropriate additives are coated on two interdigitated Au contacts, which previously patterned on an insulator support, such as Al₂O₃. Failure to spontaneous recovery in the sensor's operating conditions causes to a problem in the application of this structure as an NO₂ sensor. In this letter, we show that if K₂CO₃ is combined with Al₂O₃ in the form of a pellet and Au contacts are transferred to the top of the structure, a new device is obtained that can detect NO₂ at room temperature in both resistometric and potentiometric modes. In resistometric mode, this sensor exhibits response and recovery time of 65 and 473 s upon exposure to 900 ppb NO₂ at room temperature. Under the same conditions, these times reduce to 16 and 62 s, respectively, when the sensor is operating in potentiometric mode. Using both measurement modes, the relative accuracy of the sensor for prediction of NO₂ concentration level from 15 ppb to 900 ppb is less than 25%. Brick-wall modeling of the grains for resistometric mode and Nernstian electrochemical cell for potentiometric mode could successfully interpret the experimental behavior of the K₂CO₃/Al₂O₃ composite pellet in the exposure of NO₂.

Exploring the part load lean limit of a direct injection spark ignition engine fueled with ethanol

Stringent environmental legislation demands development of internal combustion engines seeking higher thermal efficiency to reduce greenhouse gas emissions. Brazilian governmental programs like ROTA 2030 and RenovaBio drive the research and development of highly efficient engines fueled with biofuels, like sugarcane bioethanol, that has a near to zero carbon footprint. Some technologies such as gasoline direct injection, variable valve train, and turbocharging were implemented in downsized Spark Ignition (SI) engines in order to reach higher thermal efficiencies and decrease CO2 emissions. Homogeneous lean combustion in SI operation can improve fuel consumption and reduce exhaust gas emissions. However, it is limited by combustion instability and the three-way-catalyst (TWC) inability to work properly converting nitrogen oxides (NOx). With lean combustion the NOx emissions could be significantly reduced, enabling the use of lean NOx trap (LNT) as an effective lower cost after treatment system. To explore the limits of homogeneous lean combustion in SI engines, experimental tests were performed to investigate performance, efficiency, combustion, and emission parameters of a multi-cylinder Ford 1.0l Ti-VCT EcoBoost engine fueled with hydrous ethanol. Hydrous ethanol is a commercial Brazilian fuel which has greater laminar flame speed and higher dilution tolerance than gasoline, and thus can increase combustion stability. Different fuel direct injection strategies were explored at part load (below 8.0 bar IMEP) at engine speed of 1500 rpm. Air-to-fuel ratio was varied from stoichiometric (lambda 1.0) to lambda 1.5. The limit of stable homogeneous lean combustion (COVIMEP ≤ 3.0%) was achieved in lambda 1.4. The lowest indicated load of 2.1 bar IMEP was limited by combustion stability at lambda 1.3. The maximum indicated efficiency was 36.9% at indicated load of 8.0 bar IMEP and lambda 1.4. The NOx emissions dropped below 1.4 g/kWh at 4.0 bar IMEP and lambda 1.4.