Lean-burn Gas Engine Research Articles

Modeling and Experimental Validation of Pre-Chamber Jet Penetration Considering Jet Density and Ejection Pressure Variations

Abstract Although pre-chamber (PC) is regarded as a promising solution to enhance ignition in lean-burn gas engines, a lack of comprehensive understanding of PC jet penetration dynamics remains. This study proposed a zero-dimensional (0-D) model for PC jet penetration, considering the mixing of combustion products and unburned gases and floating ejection pressure. A combustion completion degree was defined employing fuel property and heat release to estimate varying jet density. Pressure differences between PC and the main chamber (MC) were referred to as the ejection pressure. Then, this model was validated against experiments from a constant volume chamber and a rapid compression and expansion machine with CH4-H2 blends at different equivalent ratios. Results showed that the proposed model can provide a good prediction in stationary and turbulent fields with the calibrated model coefficient. The overall jet penetration exhibits a t0.5 dependence due to its single-phase characteristic and the relative lower density compared to ambient gas in MC. The flame propagation speed and heat release in PC influence the combustion completion degree at the start of jet ejection, the mass fraction of burned gas in jet increases with the equivalent ratio. Jet penetration is primarily driven by ejection pressure, with tip dynamics barely affected by the pressure difference after the peak. Tip penetration intensity increases with increased fuel equivalent ratio and H2 addition, owing to the faster flame propagation. These findings can offer useful suggestions for model-based design and combustion model development for gas engines.

Analysis of effects of pre-chamber orifices on torch flame behaviours in lean-burn gas engines

Fuel conversion from heavy oil to natural gas is favoured as a quick remedy for GHG re-duction from industrial engines in ship propulsion and power generation fields thanks to fewer carbon contents in natural gas. In medium-speed gas engines, the ejection of torch flame from a pre-chamber is often used to promote flame propagation within a main com-bustion chamber. Although orifice specifications affect the ejection behaviour of the torch flame and the following combustion in the main chamber, the effects are difficult to fully understand. Some of the authors developed a constant-volume combustion vessel that simu-lated the combustion chamber around the top dead centre of a pre-chamber type gas engine and observed the effects of orifice specifications on the torch flame ejection and the com-bustion in the main chamber. Still, the correlation was not concluded due to the lack of physical examination. In the paper, the above measurement results were confirmed by using RANS-type CFD considering the larger scale of the target engines, and the physical back-ground of the effects of orifice specifications was successfully reproduced.

Harnessing NOx emission management: A virtual sensor model for natural gas power generation engines with active pre-chamber

This paper presents a NOx Sensor machine learning model for a highly efficient 2MW power generation lean burn gas engine with an active pre-chamber. As gas power generation continues to evolve, engine efficiency and the accurate measurement of NOx emissions has taken on greater importance. However, the working life of existing NOx sensors pales in comparison to the lifecycle of an engine. This paper studies a series of machine learning NOx sensor models and carries out a comparative analysis. We introduce a predictive analytics model used for monitoring the emissions of active pre-chamber gas engines. This real deployment aims to detect the deviations in emissions across an entire fleet of gas engines, even when no physical sensors are installed in the engines. Finally, a model has been implemented that allows the prediction of NOx values, in engines that did not have them initially, with a 5–10 % precision. For example, with NOx at 120 ppm, the virtual sensor provides values close to +-10 ppm. It has been observed that such features as the setpoint value of the active pre-chamber gas pressure, in a lean burn gas engine with active pre-chamber, are among those parameters that have the greatest impact on the model estimation.

Numerical Simulation of a Prechamber-Ignited Lean-Burn Gas Engine by means of Predictive Combustion Models

Numerical Simulation of a Prechamber-Ignited Lean-Burn Gas Engine by means of Predictive Combustion Models

Experimental mild conversion of a lean burn natural gas engine with SCR to a hydrogen engine: NOx and GWP potential for marine applications

Emissions of nitrogen oxides (NOx) from marine propulsion systems have gained public interest resulting in emission limits as defined by the International Maritime Organization (IMO) with IMO Tier III, especially for vessels operating in Emission Control Areas (ECA). The reduction of greenhouse gas emissions is also increasingly important for marine propulsion. Minimizing NOx while reducing climate impact calls for technologies such as the gas engine with aftertreatment systems, preferably with the ability to run on alternative fuels. A proven technology for reducing NOx in marine engines is the Selective Catalytic Reduction (SCR) aftertreatment system. It is also possible to avoid engine raw emissions by shifting the combustion process to lower temperature levels. Hydrogen is an alternative fuel with combustion properties enabling premixed operation at significantly higher air-fuel ratio than natural gas (NG) and thus, reducing raw NOx emissions. The study uses a systematic approach to compare emissions and efficiency of a lean-burn gas engine with a natural gas and a mild conversion hydrogen setup, utilizing two different strategies: combustion of NG with the assumption of an SCR catalyst and high raw NOx emissions and combustion of pure hydrogen using the NOx reduction potential of higher excess air. The scope of the study makes it possible to illustrate engine concepts for future applications in the displacement class of 4.8 L per cylinder. The highest efficiency of 45.3% was achieved with the natural gas engine and SCR. The concept with the lowest Global Warming Potential (GWP) was the hydrogen fueled engine under the prerequisite of using green hydrogen, accompanied by a reduction in efficiency of 0.6% compared to the efficiency optimum of NG with SCR. Assuming the use of gray hydrogen, the GWP was 48% and 52% higher than with NG and NG with SCR, respectively, at the efficiency-optimal operating points.

Effects of propeller load fluctuations on performance and emission of a lean-burn natural gas engine at part-load conditions

Providing stable combustion of lean-burn natural gas engines was always a big challenge, particularly during a low load operation. In transient sea conditions, there is an additional concern due to irregular time-varying loads. Therefore, this study aimed at investigating the part-load operation of a marine spark-ignition lean-burn natural gas engine by simulating the entire engine. The engine's essential components are modeled, including air manifold, intake valves, fuel system, controllers, combustion chamber, exhaust valves, exhaust manifold and turbocharger.In steady-state, the results of emission compounds from modeling have been compared to measured data from 25% to 100% loads. For transient conditions, for the sample time of about 50 min, the fuel flow and turbocharger output are selected from the vessel logged data and compared with the simulation results. The model has shown the great potential of predicting the engine response throughout the steady-state and transient conditions. Simulating the engine at part-load transient condition showed that the unburned hydrocarbon formation, known as methane slip in lean-burn gas engines, is more than the part-load steady-state. This increase of methane slip is due to the combustion instability in lower loads and flame extinguishing in such transient conditions. The engine measured data shows a double amount of methane slip in a 25% load than the 100% load in steady-state. However, the simulation output in the transient conditions confirms an increase in methane slip over four times than equivalent steady-state load. Moreover, the lean-burn gas engine releases less NOX in part-load operation in a steady-state due to lower in-cylinder temperature. In transient conditions, there is remarkable instability in excess air ratio. Due to this instability, there is a rich mixture in instantaneous time steps during loads up. Therefore, it will result in an unusually high amount of NOX, and more than two times in comparison with the equivalent steady-state output.

Composition of Particulate Matter Emitted from Lean Burn Gas Engine with Pre-chamber Spark-plug Ignition System and Comparing Emissions with Those from Diesel Engines

When investigating the sources of particulate matter (PM) and its reduction methods, it is important to clarify its composition. In this study, PM emitted from a lean burn gas engine with a pre-chamber spark plug ignition system was analyzed by quantifying emission factors of PM components, namely Elemental Carbon (EC), Organic Carbon (OC), sulfate and nitrate, as well as “the other components” . These emission factors were compared with previous results of PM constituents emitted from diesel engines in an attempt to gauge how this gas engine could contribute to reducing PM emissions. At 75% engine load, the percentages of EC, OC, sulfate and nitrate in PM were less than 3%, 70%, less than 1% and 10% respectively with the other components being the remaining 18%. The low proportion of EC was caused by lean fuel conditions inside the gas engine. OC, which accounted for a majority of PM, is thought to have derived from vaporized lubricant oil. A slight amount of sulfur may have originated in either sulfur contents in lubricant oil or odorous components in city gas. At any engine load, the gas engine’s PM emissions were more than 70% lower than those from diesel engines. Two-thirds of reductions in PM emissions came from EC and the remaining one-third were due to a drop in emissions of the other components.

Multi-input model predictive speed control of lean-burn natural gas engine in range-extended electric vehicles

This study presents a multi-input model predictive speed control of lean-burn natural gas engine in a range extender to improve the responsiveness and anti-disturbance ability of the system. Lean combustion is recognized as an effective strategy to improve the economy and emission performance of the natural gas engine. However, the engine torque is insufficient compared with a normal combustion mode, which will result in a degraded anti-disturbance and low response performance in an engine speed tracking system in the range extender. In order to improve the performance of the lean-burn gas engine speed system, the air-fuel ratio (AFR) additional torque is introduced as another input of the system besides the throttle valve to increase the engine transient output torque, where the AFR additional torque is produced by setting AFR deviation from the nominal value. A multi-input model predictive control (MPC) controller is designed to handle the multiple inputs and constraints, guaranteeing that the AFR returns to the nominal value at steady state for efficiency and emissions, and an improved fast MPC algorithm is proposed to reduce the computation effort of the MPC strategy. Moreover, the proposed controller is evaluated by co-simulations on the platform of Matlab/Simulink with GT-Power and experiments on a range extender.

Development of a zero-dimensional method for thermodynamic analysis and NOx calculation in the prechamber of a lean-burn gas engine

Significant improvements in the power density and efficiency of lean-burn large gas-engines with a prechamber and their high flexibility in meeting fluctuating power requirements illustrate the potential for using these engines in stationary power generation and in the transportation sector. Since these engines have comparatively low CO2 and NOx-emissions, they are seen as a promising solution to meet stricter emission standards. However, current combustion concepts for these engines must be enhanced to improve their performance and emission behavior; simulation methods play a major role in this process. It is critical to know and understand the fundamental processes and their relationships in the prechamber and main combustion chamber; conducting detailed analyses makes this possible. Zero-dimensional methods are suitable for these analyses. Due to their shorter calculation times, they allow extensive parameter variations to be investigated. Common methods in this area are limited to calculating performance and emission related values only in the main combustion chamber. Since a considerable share of NOx-emissions from high-performance lean-burn gas-engines arise in the prechamber, it is imperative to conduct a separate thermodynamic analysis of the prechamber and its interaction with the main combustion chamber. This paper presents a zero-dimensional method with which NOx-emissions from the prechamber can be calculated separately from the emissions of the main combustion chamber. To this end, it is necessary to conduct thermodynamic analyses of both the chambers and to consider their interaction. The measurement data for development and validation of this method is provided by tests on a single-cylinder engine with separate cylinder-pressure indication for both the chambers. Based on the results of the analyses, it can be determined to what extent each of the two systems is involved in the formation of nitrogen-oxides. With knowledge of the origin of NOx-emissions, measures may be enacted that reduce total NOx-emissions.

Fuel consumption and emission reduction of marine lean-burn gas engine employing a hybrid propulsion concept

As the emission legislation becomes further constraining, all manufacturers started to fulfill the future regulations about the prime movers in the market. Lean-burn gas engines operating under marine applications are also obligated to enhance the performance with a low emission level. Lean-burn gas engines are expressed as a cleaner source of power in steady loading than diesel engines, while in transient conditions of sea state, the unsteadiness compels the engine to respond differently than in the steady-state. This response leads to higher fuel consumption and an increase in emission formation. In order to improve the stability of the engine in transient conditions, this study presents a concept implementing a hybrid configuration in the propulsion system. An engine model is developed and validated in a range of load and speed by comparing it with the available measured data. The imposed torque into the developed engine model is smoothed out by implementing the hybrid concept, and its influence on emission reduction is discussed. It is shown that with the hybrid propulsion system, the NOX reduces up to 40% because of the maximum load reduction. Moreover, eliminating the low load operation by a Power Take In during incomplete propeller immersion, the methane slip declines significantly due to combustion efficiency enhancement.

Dynamic Estimation Method of Effective Active Site on Palladium Methane Oxidation Catalyst in Exhaust Gas of Marine Lean Burn Gas Engine

Abstract Lean-burn gas engines have recently attracted attention in the maritime industry, because they can reduce NOx, SOx, and CO2 emissions. However, since methane (CH4) is the main component of natural gas, the slipped methane, which is the unburned methane, likely contributes to global warming. It is thus important to make progress on exhaust after-treatment technologies for lean-burn gas engines. A Palladium (Pd) catalyst for CH4 oxidation is expected to provide a countermeasure for the slipped methane, because it can activate at lower exhaust temperature comparing with platinum. However, a de-activation in higher water (H2O) concentration should be overcome because H2O inhibits CH4 oxidation. This study was performed to investigate the effects of exhaust temperature or gas composition on active Pd catalyst sites to clarify CH4 oxidation performance in the exhaust gas of lean-burn gas engines. The authors developed the method of estimating effective active sites for the Pd catalyst at various exhaust temperatures. The estimation method is based on the assumption that active sites used for CH4 oxidation process can be shared with the active sites used for carbon mono-oxide (CO) oxidation. The molecular of chemisorbed CO on the active sites of the Pd catalyst can provide effective active sites for CH4 oxidation process. This paper introduces experimental results and verifications of the new method, showing that chemisorbed CO volume on a Pd/Al2O3 catalyst is increased with increasing Pd loading in 250–450 °C, simulated as a typical exhaust temperature range of lean-burn gas engines.

Development and validation of a novel quasi-dimensional combustion model for un-scavenged prechamber gas engines with numerical simulations and engine experiments

Lean-burn gas engines equipped with an un-scavenged prechamber have proven to reduce nitrogen oxides (NOx) emissions and fuel consumption, while mitigating combustion cycle-to-cycle fluctuations and unburned hydrocarbon (UHC) emissions. However, the performance of a prechamber gas engine is largely dependent on the prechamber design, which has to be optimised for the particular main chamber geometry and the foreseen engine operating conditions. Optimisation of such complex engine components relies partly on computationally efficient simulation tools, such as quasi and zero-dimensional models, since extensive experimental investigations can be costly and time-consuming. This article presents a newly developed quasi-dimensional (Q-D) combustion model for un-scavenged prechamber gas engines, which is motivated by the need for reliable low order models to optimise the principle design parameters of the prechamber. Our fundamental aim is to enhance the predictability and robustness of the proposed model with the inclusion of the following: (i) Formal derivation of the combustion and flow submodels via reduction of the corresponding three-dimensional models. (ii) Individual validation of the various submodels. (iii) Combined use of numerical simulations and experiments for the model validation. The resulting model shows very good agreement with the numerical simulations and the experiments from two different engines with various prechamber geometries using a set of fixed calibration parameters.

Understanding sulfur poisoning of bimetallic Pd-Pt methane oxidation catalysts and their regeneration

Pd-Pt/Al2O3 and Pd-Pt/CeO2-ZrO2-Y2O3-La2O3 methane oxidation catalysts were investigated under typical lean-burn gas engine conditions with respect to sulfur poisoning and during reactivation, particularly under the most efficient rich conditions. Sulfation of the noble metal and the support material led to pronounced catalyst deactivation. A pronounced transfer of sulfates to the support, particularly alumina, only partially protects the noble metal. In situ X-ray absorption spectroscopy gave insight into the nature and evolution of Pd species during regenerative treatment. Although palladium sulfate that formed during poisoning is decomposed at approximately 200 °C in oxygen-free conditions, support regeneration requires higher temperatures, which result in PdS formation above 400 °C. Despite its high stability under rich conditions, PdS decomposition by oxidation in lean atmosphere leads to the recovery of the activity. In addition, water vapor that is present during the rich regeneration exhibited a beneficial effect on the regeneration with higher catalytic activity after regeneration.

In situ Activation of Bimetallic Pd−Pt Methane Oxidation Catalysts

AbstractThis study investigates possible pathways to reduce water inhibition over Pd−Pt methane oxidation catalysts supported on alumina and a ceria‐zirconia mixed oxide under conditions typical for lean burn gas engines. Spatially resolved concentration and temperature profiles reveal that addition of hydrogen to the lean reaction mixture leads to significant heat production and an increase in methane conversion. Moreover, reductive pulses during operation are not only able to regenerate the catalyst deactivated by water by removal of OH‐groups from the catalyst surface, but even promote its activity after repeated application of pulsing for several hours. X‐ray absorption spectroscopy reveals the formation of a partially reduced PdO−Pd mixture during the pulsing, which explains the increase in activity. This state of high activity is stable for several hours under the tested lean conditions. The results presented in this study suggest an efficient in situ activation strategy to overcome water inhibition of methane total oxidation over Pd−Pt catalysts by careful process control.

Unburned hydrocarbon formation in a natural gas engine under sea wave load conditions

Although natural gas is documented as a low-emission fuel compared to the other traditional fossil fuels in internal combustion engines, recent research indicates large amounts of methane emission released by lean burn gas engines and highlights the importance of this emission on global warming. This paper aims at illustrating the main sources of unburned fuel in internal combustion engines with an emphasis on spark ignited natural gas engines. In addition, two unburned hydrocarbon modeling patterns, empirical and thermodynamic, are proposed. Moreover, a verified engine model including all components with an implemented dynamic load based on harmonic sea waves has been set up and coupled to the unburned hydrocarbon formation models. Results show that load variation may contribute to further methane slip and this increment rises sharply when the load amplitude enlarges. The maximum amount of methane slip occurs at reduced loads when the time lag of the control system of the turbocharger causes additional fresh air to flow towards the combustion chamber and brings the flame into the quenching area. As well, inspecting unburned hydrocarbon emission in diverse air–fuel ratios but with the same wave frequency and amplitude uncovers the sensitivity of lean burn gas engines to the dynamic load.

Quasi-Dimensional Multi-Zone Combustion Diagnostic Tool for SI Engines with Novel NOx and CO Emissions Models

<div class="section abstract"><div class="htmlview paragraph">In this work a quasi-dimensional multi-zone combustion diagnostic tool for homogeneous charge Spark Ignition (SI) engines is analytically developed for the evaluation of heat release, flame propagation, combustion velocities as well as engine-out NOx and CO emissions, based on in-cylinder pressure data analysis. The tool can be used to assess the effects of fuel, design and operating parameters on the SI engine combustion and NOx and CO emissions formation processes.</div><div class="htmlview paragraph">Certain novel features are included in the presently developed combustion diagnostic tool. Firstly, combustion chambers of any shape and spark plug position can be considered due to an advanced model for the calculation of the geometric interaction between a spherically expanding flame and a general combustion chamber geometry. Also, the temperature stratification of the burned gas developed during the combustion phase, which has to be captured for the theoretically realistic estimation of the in-cylinder formation of pollutant emissions, is taken into account by a multi-zone thermodynamic treatment. According to this, multiple spherically allocated burned zones are sequentially generated at specified (user-defined) crank angle intervals, forming overlapping shells. Moreover, complex chemical equilibrium compositions are computed, which can include any user-defined mixture of species in the combustion products, using an advanced modular method based on the minimization of Gibbs energy. Furthermore, NOx and CO engine-out emissions are calculated based on novel in-cylinder formation models presented by the authors in the past. Specifically, NOx emissions are evaluated by a global algebraic NOx emissions formation model, accounting for both thermal and N<sub>2</sub>O pathway NO formation, based on the calculation of the characteristic timescales of the relevant NO formation mechanisms. CO emissions are assessed using a new kinetics-based model, consisting of a single Ordinary Differential Equation (ODE) that can be analytically integrated. The CO emissions model is derived considering the dynamics of a representative pool of active radicals in post-flame gases and explicitly describes the CO oxidation quenching process.</div><div class="htmlview paragraph">The combustion diagnostic tool is applied to a lean burn gas engine at various engine speeds under full load conditions and constant lambda value. Various combustion and NOx and CO emissions related results are presented and discussed to illustrate the capabilities of the tool for combustion diagnosis, while at the same time calculated engine-out NOx and CO emissions are found to be in satisfactory agreement with measured ones.</div></div>

Influence of Hydrogen Addition on Combustion and Exhaust Characteristics in a Lean-burn Gas Engine

Influence of Hydrogen Addition on Combustion and Exhaust Characteristics in a Lean-burn Gas Engine

A Study on the Influence of Hydrogen Addition on Combustion and Exhaust Characteristics in a Lean Burn Gas Engine for Power Generation (Second Report)

A Study on the Influence of Hydrogen Addition on Combustion and Exhaust Characteristics in a Lean Burn Gas Engine for Power Generation (Second Report)

PGM based catalysts for exhaust-gas after-treatment under typical diesel, gasoline and gas engine conditions with focus on methane and formaldehyde oxidation

The HC and CO oxidation activity of Pt/Al2O3, Pd/Al2O3 and Pd-Pt/Al2O3 catalysts was compared under three exhaust-gas model conditions typical for stoichiometric gasoline as well as lean burn diesel by means of temperature programed conversion tests on laboratory test benches. In order to understand the differences in emission reduction performance, the impact of gas mixture composition was systematically studied with a particular focus on methane and formaldehyde conversion.The catalysts used in this study were prepared by incipient wetness impregnation of Al2O3 followed by washcoating on ceramic honeycombs, and were pre-treated in an equal manner before each activity test.Distinct differences in pollutant conversion were observed over the three catalysts under the investigated conditions. Pd-based monometallic and bimetallic catalysts revealed the lowest temperature for CH4 oxidation (<450 °C) under lean conditions, being lower under lean Diesel than Compressed Natural Gas (CNG) conditions. The reason for this behavior seems to be the higher water concentration in the CNG gas mixture. Furthermore, it was found that the presence of HCs shifts the conversion of methane to higher temperatures, most probably due to produced water during combustion of the HCs. Pt/Al2O3 on the other hand only converts methane at temperatures above 500 °C but no sensitivity to water or the amount of additional HCs was observed. The lowest light-out temperature for formaldehyde oxidation in excess of oxygen was measured on Pt/Al2O3 with full conversion below 125 °C. While this was the case for a model gas mixture of HCHO, H2O and O2, under simulated lean burn gas engine conditions, formaldehyde is oxidized at lower temperature on Pd-Pt/Al2O3 than on Pt/Al2O3 due to the strong inhibiting effect of CO on Pt-particles.Under stoichiometric gasoline conditions, Pt had the highest activity for methane oxidation whereas Pd/Al2O3 and Pd-Pt/Al2O3 hardly convert methane below 500 °C. Unsaturated HCs and CO on the other hand were converted at lower temperature over Pd containing monometallic and bimetallic catalysts in comparison to Pt/Al2O3, showing once again the multiple and complex effects generated by variations in exhaust gas mixture and catalyst composition.

Study with Micro-reactor on Deactivation of Pd Methane Oxidation Catalyst for Marine Lean Burn Gas Engines

Study with Micro-reactor on Deactivation of Pd Methane Oxidation Catalyst for Marine Lean Burn Gas Engines