Pre-chamber Ignition Research Articles

Future gasoline engine ignition: A review on advanced concepts

To meet the future requirements of fuel economy and exhaust emissions, high-efficiency gasoline engines tend to employ diluted combustion concepts along with intensified charge motion and stratified mixtures. Securing the ignition of such mixtures over the full engine operation range is challenging, because of the lowered mixture reactivity and increased discrepancy of stoichiometry. In recent years, increasing research efforts have been spending on innovations of ignition technologies to tackle the challenges. In this paper, the directions of ignition improvement are highlighted based on the fundamental understanding of the ignition mechanisms. The working principles of the primary types of advanced ignition systems are introduced; and relevant engine and combustion vessel test results are reviewed. The ignition systems are categorized as: (1) high-energy spark ignition, (2) pulsed nanosecond discharge ignition, (3) radio-frequency plasma ignition, (4) laser-induced plasma ignition, and (5) pre-chamber ignition. The advanced ignition systems are commented, regarding the ignition effectiveness and the implementation challenges, according to the literatures and the extensive empirical work at the authors’ laboratory.

A comparative study to evaluate the effects of pre-chamber jet ignition for engine characteristics and emission formations at high speed

The pre-chamber ignition technology is a good solution that can make spark-ignition engines gradually more efficient. The novelty of the study is the testing of the pre-chamber jet ignition according to detailed air-fuel mixture range and fuel injection rates by combustion chambers. The main points in using this pre-chamber jet ignition were to observe the effect of reducing fuel consumption and emission formation. The tests were carried out for 0.80–1.80 lambda ranges and the pre-chamber injection/main chamber injection mass ratio ranges. A commercial RON 98 fuel was used at two ignition modes in tests for 5000 rpm high engine speed. At the pre-chamber jet ignition usage, the in-cylinder pressure for 1.00 lambda is overall 1.78% and 19.89% higher than the 0.80 lambda and the 1.80 lambda. The brake specific fuel consumption is about 8.67% lower than the spark-plug ignition usage at 0.80–1.20 lambda range. The HC formation is overall 8.12% lower than the spark-plug usage. The NOx formation for the spark-plug ignition is approximately 53.97% higher than the pre-chamber jet ignition usage as the temperature in-cylinder is high. The pre-chamber jet ignition was led to a much shorter flame development time and better combustion stability than the spark-plug.

Simulation-Aided Development of Prechamber Ignition System for a Lean-Burn Gasoline Direct Injection Motor-Sport Engine

Abstract Due to recent regulation changes to restricted fuel usage in various motor-sport events, motor-sport engine manufacturers have started to focus on improving the thermal efficiency and often claim thermal efficiency figures well above equivalent road car engines. With limited fuel allowance, motor-sport engines are operated with a lean air–fuel mixture to benefit from higher cycle efficiency, requiring an ignition system that is suitable for the lean mixture. Prechamber ignition is identified as a promising method to improve lean limit and has the potential to reduce end gas auto-ignition. This paper analyses the full-load performance of a motor-sport lean-burn gasoline direct injection (GDI) engine and a passive prechamber is developed with the aid of a computational fluid dynamics (CFD) tool. The finalized prechamber design benefited in a significant reduction in burn duration, reduced cyclic variation, knock limit extension, and higher performance.

Numerical investigation of lambda-value prechamber ignition in heavy duty natural gas engine

Turbulent Jet Ignition systems are mainly dedicated to the combustion of lean mixtures of natural gas in heavy duty engines. The use of such a system in combination with lean mixtures leads to an increase in its overall efficiency. The article presents simulation analyzes of the impact of the excess air coefficient occurring in prechamber on the combustion process: combustion indicators and emission indicators. Tests on a single-cylinder engine with a displacement of about 4 dm3 at medium mixture (IMEP = 1.0 MPa) were carried out using the AVL Fire software. It was found that the incineration of global lean mixtures (lambda = 2) is effective when initiating this process (in the prechamber) with a charge of a stoichiometric composition. A strong relationship was found between the thermodynamic indicators in both prechamber and main chamber and the excess air coefficient initiating combustion.

Computational assessment towards understanding the energy conversion and combustion process of lean mixtures in passive pre-chamber ignited engines

In this paper, a computational study was performed using a combination of several numerical tools to better understand the limiting aspects of combustion in a passive pre-chamber ignition system when operating at lean conditions. A specific methodology was developed to analyze in detail the scavenging and combustion processes of this ignition concept. Results show how the scavenging of passive pre-chambers is primarily dependent on the force that the piston makes on the gas during the compression stroke, being independent of the pre-chamber geometry as along as the ratio between the total cross sectional area of the pre-chamber holes and the pre-chamber volume is kept within a suitable range. Moreover, a successful lean combustion, with an air-to-fuel ratio around 2, cannot be achieved as the burning rates inside the pre-chamber significantly decrease due to the low laminar flame speeds, that results in low quality jets. Further results show that increasing the flow temperature can help to recover competitive combustion rates when knocking combustion is not a limiting factor. The contribution of the heat losses through the pre-chamber walls to the overall energy balance of the pre-chamber has been estimated, showing that their impact is negligible (<5%). Alternatives for increasing the laminar flame speed were proposed in order to improve combustion inside the pre-chamber. Although the pre-chamber combustion profile was successfully improved, none of the proposed solutions were able to completely burn the main chamber charge with the current pre-chamber design.

Exploring the lean limit operation and fuel consumption improvement of a homogeneous charge pre-chamber torch ignition system in an SI engine fueled with a gasoline-bioethanol blend

The transportation sector faces a big energy challenge as it looks for more advanced technologies and renewable sources, in which pre-chamber ignition systems and bioethanol have gained worldwide recognition. In this manuscript, a homogenous torch ignition (HTI) system was experimentally analyzed in a commercial four-cylinder engine equipped with port-fuel injection and fueled with a gasoline-bioethanol blend with 25% of bioethanol by volume (E25). Tests were performed at a wide range of speeds and loads for stoichiometric and lean mixtures. Through in-cylinder pressure measurement, a combustion analysis was carefully carried out. Results show that the HTI system leads to a much faster combustion rate and low engine cycle-to-cycle variation due to enhanced ignition energy and turbulence levels in the main chamber, and is able to extend the lean combustion limit with acceptable combustion covariance up to λ = 1.30. Moreover, improved combustion phasing combined with reduced pumping losses and lower heat transfer to the cooling system decreased fuel consumption. BSFC was improved up to 8.4%, 12.1% and 10.2% for engine speeds of 2500, 3500 and 4500 rpm, respectively, for the 3.5 and 4.6 BMEP conditions at λ = 1.20, while the higher load (5.8 bar BMEP) was improved up to 8.6% at λ = 1.30.

Prechamber ignition: An exploratory 2-D DNS study of the effects of initial temperature and main chamber composition

A numerical investigation was conducted to study ignition and the initial phases of methane combustion in a two-dimensional setup consisting of a pre- (PC) and main (MC) chamber. The effect of the wall thermal boundary condition (isothermal Tw=500 K or adiabatic), initial mixture temperature (Tu=300 and 800 K) and equivalence ratio in the main chamber (ϕMC=0.5 and 1.0) was studied. A stoichiometric mixture was used in the PC and the mixtures were initially quiescent in all cases. Flame propagation in the prechamber is affected mainly by the initial temperature, while the thermal state of the wall plays a minor role. The transient jet that is generated at the exit of the orifice connecting the two chambers creates an intense flow field with vortical structures that, depending on the initial temperature, persist for a long time or dissipate quickly affecting combustion in the main chamber. Depending on the local flow and mixing conditions close to the orifice exit, the hot jet can be broken into small kernels at low Tu or forms quickly a flame torch at hot conditions, strongly affecting ignition of the MC mixture and flame propagation in the main chamber. In the lean MC cases, the intense mixing with the stoichiometric PC mixture creates local compositions that are more favorable for ignition by the hot turbulent reactive jet that subsequently exits from the PC at a temperature that is significantly lower than the adiabatic flame temperature of the corresponding mixture. Despite the short residence time, the reactive state of the mixture is affected as it flows through the nozzle. The flame structures in the MC are described in terms of the progress variable and mixture fraction and compared to flamelet-type calculations. The local flame structure differs strongly from that of the 1-D unstrained premixed flame, particularly for the low Tu cases. The flamelet-type calculations show that ignition of the most reactive mixture is enhanced by the radicals in the hot reactive jet, while scalar dissipation rate accelerates the ignition of the whole mixture. The 2-D simulations show that ignition is significantly longer than what is predicted by the flamelet calculations.

Comparison of open chamber and pre-chamber ignition of methane/air mixtures in a large bore constant volume chamber: Effect of excess air ratio and pre-mixed pressure

Natural gas is an alluring choice to substitute the widely used diesel for environmental and economic reasons as it generates less particulate matter and carbon dioxide emissions. However, natural gas is comparatively difficult to be ignited and its flame penetrates slowly in a large bore combustion chamber especially for the lean condition. In order to analyze how the pre-chamber turbulent jet ignition promotes combustion in a large volume chamber, a comparative study with the traditional open chamber ignition mode was conducted to analyze the effect of excess air ratios and pre-mixed pressures on the combustion characteristics of methane/air mixtures. In rich fuel combustion, the advantage of pre-chamber is not obvious, and the flame propagation rate can only be increased by 2.8 times in maximum. In the case of lean combustion and stoichiometric combustion, the flame propagation speeds can be increased by 5–6 times, especially in lean combustion by pre-chamber. In general, the pre-chamber turbulent jet ignition technique can increase the flame propagation rate of methane/air, and improve combustion and thermal efficiency of natural gas large-bore engines under lean combustion conditions. With comparison to the open chamber ignition mode, the reduction percentage of ignition time by pre-chamber turbulent jet ignition decreases with the rise of initial pressure. However, the asymmetric placement of the spark plug inside the pre-chamber, results in the inhomogeneous spreading of flame jets in the constant volume chamber, which ought to be considered in the design of marine engine.

The influence of volume variation in a homogeneous prechamber ignition system in combustion characteristics and exhaust emissions

Research on prechamber ignition systems has become increasingly frequent as they promote significant reductions in engine-out emissions with low cost of implementation. In these systems, the combustion starts in an auxiliary chamber and flows through the interconnecting holes, in form of jets, to the main chamber, where it ignites the air–fuel mixture contained therein. Besides the air–fuel ratio, the geometry of the prechamber presents fundamental parameters that influence combustion characteristics and, consequently, the exhaust emissions. This paper aims to evaluate the effects of prechamber volume variation in combustion and emissions of a commercial engine equipped with a homogeneous charge prechamber ignition system. For this, three volumes were considered in stationary tests of a multi-cylinder engine operating under stoichiometric conditions in 1500 rpm and 3.3 bar of IMEP. The results indicated that the increase in volume within the limits considered present increase in the energy released and, hence, in the burning speed, reducing the combustion duration. Comparing to the baseline spark plug system, the prechamber with 3.8% of the main combustion chamber volume presented the best configuration among the evaluated volumes, with an increase in the evolution of pressure traces and reductions in around 13% in unburned hydrocarbons (HC) and nitrogen oxides (NOx) engine-out emissions.

Potential of bio-ethanol in different advanced combustion modes for hybrid passenger vehicles

The strong new restrictions in the vehicle CO2 emissions together with the instability of the fossil fuels reserves reinforces the necessity to continue developing high efficiency combustion engines that operate with renewable energy sources. Bio-ethanol appears as a potential fuel to replace well-established fossil fuels, such as gasoline, due to the overall carbon neutral emission. In addition, the high-octane number allows to increase the compression ratio of the engine to improve the thermal efficiency. Apart from the CO2, the emissions legislation restricts the NOx and particle matter emissions to ultra-low values, and they will continue decreasing down to almost zero. In this work, two advanced dual-fuel combustion modes using bio-ethanol as main fuel are studied. A pre-chamber ignition system (PCIS) using bio-ethanol and hydrogen, and a reactivity-controlled compression ignition (RCCI) combustion mode operating with bio-ethanol/diesel was selected due to the potential to reduce NOx emissions. These combustion technologies were studied by a numerical 0-D vehicle simulations in homologation and real-life driving cycles for a range extender hybrid powertrain. As a baseline, the original manufacturer spark ignition (SI) no-hybrid powertrain fueled with pure bio-ethanol was used. The powertrain components and control system were optimized to obtain the maximum overall vehicle efficiency, and low CO2-NOx emissions. Finally, a life cycle analysis (LCA) was performed to study the global potential of the bio-ethanol to reduce greenhouse gas (GHG) emissions. A battery electric vehicle (BEV) and a gasoline SI no-hybrid vehicle were added for comparison. The results show that the RCCI mode presents the highest potential to reduce the NOx emissions. However, the PCIS allows to reduce the tank to wheel CO2 emissions up to 60 g/km when high rates of H2 are used. The LCA-GHG for the vehicles using bio-ethanol is 50% and 95% lower than a BEV and SI-gasoline vehicle, respectively.

Experimental and Numerical Study of a Methane-Fueled Pre-chamber System in Rapid Compression Machine

ABSTRACT Pre-chamber jet ignition is a promising combustion technology to accelerate burning velocity and improve combustion stability in natural gas engines. In this study, firstly, the ignition characteristics and the dilution limits in passive pre-chamber system with different orifice diameters were experimentally investigated based on a rapid compression machine (RCM). Methane (CH4) was used as the test fuel and CO2/N2 was used as the dilution components to simulate exhaust gas recirculation conditions in engines. Real-time combustion pressures were recorded and combustion images were captured using high-speed photography to visualize the entire jet ignition and combustion process. The experimental results showed that two different ignition behaviors were observed regarding to different orifice diameters. And no capacity of extending CO2/N2 dilution limits in the passive pre-chamber system compared to conventional spark ignition system. Then three-dimensional numerical simulations were conducted based on the experimental results. Simulation results demonstrated two ignition modes, pre-chamber jet flame ignition and pre-chamber jet autoignition, were presented due to the different jet temperatures, concentrations of immediate species, and turbulence intensities. Lastly, based on the numerical model, the effects of pre-chamber structure parameters on the ignition modes and potentials of different dilution state of mixture in pre-chamber for extending dilution limits were numerically studied. It was found that the ratio of total effective cross-sectional area of orifices to pre-chamber volume (At /VPC ) was the key structure parameter of pre-chamber systems to determined different ignition modes. And there was a narrow critical range of At /VPC to achieve pre-chamber jet autoignition (PJAI) mode, beyond which PJFI mode or ignition failure occurred. The actual dilution rate of mixture in the pre-chamber affected the ignition probability and stability in the main chamber. Improving the chemical reactivity of mixture in the pre-chamber was beneficial to effectively extend the dilution limits due to the stronger thermal, chemical, and turbulent effects of pre-chamber jet. Abbreviations: PJI Pre-chamber jet ignition; CSI Conventional spark ignition; NG Natural gas; PM Particulate matter; SI Spark ignition; CI Compression ignition; THC Total hydrocarbon; SCR Selective catalyst reduction; TWC Three-way catalyst; EGR Exhaust gas recirculation; BSFC Brake specific fuel consumption; DI Direct injection; RCM Rapid compression machine; CVB Constant volume bomb; TDC Top dead center; BDC Bottom dead center; CFD Computational fluid dynamics; SOC Start of combustion; PJAI Pre-chamber jet auto-ignition; PJFI Pre-chamber jet flame ignition; TKE Turbulent kinetics energy

Лазерное зажигание топлива жидкий кислород — газообразный водород в крупноразмерной камере сгорания

The article presents a review of the results of studies of laser ignition of a cryogenic mixture (gaseous hydrogen and liquid oxygen) in an experimental combustion chamber, carried out at the bench testing facility of KBKhA (Voronezh). A laser ignition module specially designed at the Keldysh Research Centre and with parameters optimized for use in the rocket engine launch system was used during the experiments. Fuel ignition by the laser system occurred directly in the experimental chamber without the use of an ignition device or pre-chamber. To implement this ignition method, inflammation of the fuel in the chamber was carried out by focusing the laser radiation into the mixture, with the initiation of a spark of optical breakdown in the selected area with conditions favorable for the start of combustion. The results of the experiments confirmed the efficiency of the laser module during both standalone and firing tests, including multiple launches of the propulsion unit operated on a cryogenic mixture (gaseous hydrogen and liquid oxygen).

Evaluation of a stratified prechamber ignition concept for vehicular applications in real world and standardized driving cycles

The aim of this paper is to evaluate the potential of a prechamber ignition system to reduce the exhaust emissions and fuel consumption of commercial vehicles in the conditions proposed by the standardized and real-world driving cycles. For this purpose, a multi-cylinder engine was mapped in stationary conditions using two different combustion modes. First, the engine was tested under the baseline stoichiometric combustion with a spark plug ignition system. Second, the engine map was obtained using a stratified prechamber ignition system under lean conditions. Later, the experimental data was used as input for a computer model that simulates the vehicle operation with both concepts under different driving cycles. To run the model under real-world driving conditions, experimental data was acquired in a specific region in southern Brazil in conditions of heavy and free flow. Moreover, the conditions of the study were extended including two homologation cycles, the FTP-75 and WLTC. The results for the different cycles show similar average exhaust emissions and fuel consumption between WLTC and the real conditions of free flow traffic, and also between the FTP-75 and the real conditions of heavy flow traffic. The results also point out the potential of the prechamber ignition system to achieve a reduction of the engine-out CO and NOx emissions greater than 50% and 85%, respectively, as compared to the baseline stoichiometric combustion with a spark plug ignition, without penalizing the fuel consumption.

Combustion analysis of a SI engine with stratified and homogeneous pre-chamber ignition system using ethanol and hydrogen

Environmental regulations have been increasingly demanding reduction of fossil fuel consumption and emission in industrial activities and in the transportation sector. In this context, the use of biofuels such as ethanol has become increasingly attractive. With similar purpose, several technologies have been explored, among which stands out the pre-chamber ignition system. In this context, this paper aims to evaluate the viability of pre-chamber system use in a commercial SI engine, considering combustion and emission analysis of both homogeneous and stratified with hydrogen injection pre-chamber systems. To conduct this research, a flex-fuel engine under stoichiometric conditions and ethanol as fuel in main chamber was used. In this work it was identified that the use of pre-chambers can reduce the combustion time by up to 20%, increase the thermal efficiency by up to 5% and reduce CO and NOx emissions by up to 12% and 33% respectively, when compared to the baseline ignition system, without significant changes in the combustion efficiency. Moreover, the research proves that output power in stoichiometric mixtures can be increased with the use of both pre-chamber ignition systems.

Gasoline Fueled Pre-Chamber Ignition System for a Light-Duty Passenger Car Engine with Extended Lean Limit

Gasoline Fueled Pre-Chamber Ignition System for a Light-Duty Passenger Car Engine with Extended Lean Limit

Evaluation of the passive pre-chamber ignition concept for future high compression ratio turbocharged spark-ignition engines

The pre-chamber ignition concept is an attractive strategy to enable the operation of spark-ignition engines in lean or diluted conditions keeping a suitable combustion process. According to the results the benefits in lean conditions include the combustion process shortening, the improvement of combustion stability and the increase of combustion efficiency by lowering carbon monoxide and hydrocarbons emissions. Thus, the pre-chamber ignition concept, especially in its passive version, arises as a promising alternative for future spark-ignition engines for passenger car applications. In this framework, an experimental investigation has been carried out to evaluate the potential of passive pre-chamber ignition concept in a high compression ratio, turbocharged, port fueled spark-ignition engine, using 95 Research Octane Number gasoline. As a first step, a 1D Wave Action Model was generated to design the pre-chamber geometry taking the fuel available at the start of pre-chamber combustion and the pressure difference between the main chamber and pre-chamber as key parameters. In a second step, these pre-chamber designs were experimentally validated at high load/speed conditions (4500 rpm, 12.5 bar Indicated Mean Effective Pressure) and compared with the conventional spark-ignition concept. Experimental results show how the passive pre-chamber concept increases efficiency with good combustion stability and high combustion efficiency in stoichiometric conditions. Nevertheless, maximum lambda attainable with the passive system is similar than that of the conventional spark and much lower compared to the maximum levels reported for the active system.

Large Eddy Simulation of Pre-Chamber Ignition in an Internal Combustion Engine

Using homogeneous lean mixtures is an efficient way to reduce fuel consumption and pollutant emissions in internal combustion engines. However, lean combustion requires breakthrough technologies to induce reliable ignition and fast combustion. One of these technologies uses pre-chamber to create multiple hot turbulent jets and provide ignition sites for the lean mixture. In this paper, the behaviour of a pre-chamber ignition system used to ignite the main chamber of a real engine is studied using large eddy simulation with direct integration of analytically reduced chemistry using the dynamic thickened flame model. The large eddy simulation allows to analyze the flow entering and leaving the pre-chamber, to measure the cooling and quenching effects introduced by the hot gas passages through the ducts connecting pre-and main chambers and to analyze the ignition and combustion sequences. For the case studied here, small amount of flame kernels are exhausted from the pre-chamber. Hot products penetrate the main chamber, disperse and mix with the fresh reactants and lead to ignition. The combustion in the main chamber starts in a distributed reaction mode before reaching a flamelet propagation mode.

Development of a homogeneous charge pre-chamber torch ignition system for an SI engine fuelled with hydrous ethanol

Energy is the key to wellbeing and sustainability of modern civilization and its demand continues to increase. With the end of oil availability perspectives and the world energy crisis, technological solutions are needed from the scientific community to promote the reduction of fossil fuel consumption, the maximization of fuel conversion efficiency and the reduction of emission levels in internal combustion engines. Aiming at reaching these needs, the use of a pre-chamber ignition system in spark-ignition (SI) engines is a potential alternative enabling such engines to operate with lean mixtures and with a wide variety of fuels. In this study, a methodology was developed to design and characterize experimentally a homogeneous charge pre-chamber torch ignition system fuelled with hydrous ethanol (with 6–7% in mass of water content) and using lean burn mixtures (excess air ratio (λ) > 1.0). The methodology, which has not been reported previously in other works, consisted of a one-dimensional mathematical model, that allowed for the definition of pre-chamber geometrical parameters. The device was manufactured and adapted to an SI engine, requiring no additional work to the cylinder head, as the pre-chamber was mounted in the original spark-plug screw thread. The prototype was experimentally characterized on an active dynamometer, and performance, combustion, emission and combustion visualization were studied. The pre-chamber ignition engine expanded the flammability limit in comparison with the baseline engine. For λ = 1.4, engine fuel conversion efficiency was increased by 5.4%, specific fuel consumption decreased by 22% and nitrogen oxides (NOx) emissions reduced by 52%, but total hydrocarbons (THC) emissions increased. Improvements achieved were due to the faster burn rates characterized by the reduced MBF 0–10%, combustion duration and combustion instability, and also the increased thermodynamic efficiency and the lower combustion temperatures achieved with lean burn technology. From the conclusions obtained in this research, the homogeneous pre-chamber torch ignition system developed for hydrous ethanol has potential for application and marketability integration, as an alternative technology able to help meet energy demands in a sustainable manner.

Combustion and emissions of gasoline, anhydrous ethanol, and wet ethanol in an optical engine with a turbulent jet ignition system

Turbulent jet ignition is a pre-chamber ignition system for an otherwise standard gasoline spark ignition engine. Turbulent jet ignition works by injecting chemical active turbulent jets to initiate combustion in a premixed fuel/air mixture. The main advantage of turbulent jet ignition is its ability to ignite and burn completely very lean fuel/air mixtures in the main chamber charge. This occurs with a very fast burn rate due to the widely distributed ignition sites that consume the main charge rapidly. Rapid combustion of lean mixtures leads to lower exhaust emissions due to more complete combustion at lower combustion temperature. The purpose of the paper is to study the combustion characteristics of gasoline, ethanol, and wet ethanol when operated with the pre-chamber combustion system and the ability of the pre-chamber ignition to extend the lean-burn limits of such fuels. The combustion and heat release process was analyzed and exhaust emissions measured. Results show that the effect of turbulent jet ignition system on the lean-burn limit and exhaust emissions varied with fuels. The lean limit was extended by using fueled pre-chamber furthest, to λ = 1.71 with gasoline, followed by λ = 1.77 with wet ethanol and λ = 1.9 with ethanol. NOx emissions were significantly reduced with increased lambda for each fuel under stable combustion conditions. For ethanol, at maximum lean limit lambda 1.9, the NOx emissions were almost negligible due to lower combustion temperature.

Control-oriented analysis of a lean-burn light-duty natural gas research engine with scavenged pre-chamber ignition

Natural gas is well-suited as a fuel in the transport sector. Due to its excellent combustion characteristics, engines operating with compressed natural gas (CNG) reach high efficiency, especially if operated at lean conditions. However, CNG engine research mainly focusses on stoichiometric conditions in order to use a three-way catalytic converter for the exhaust gas after treatment system. With the objective to explore the potential of CNG engines operated at lean conditions, a turbo-charged CNG engine with high com-pression ratio is developed and optimized for lean operation. In order to increase the ignition energy, the CNG engine is equipped with scavenged pre-chambers. A specific control structure is developed, which allows to operate the engine at a pre-defined (lean) air-to-fuel ratio. Further functionalities such as the combustion placement control and algorithms to estimate the conditions inside of the pre-chamber are implemented. The first part of this paper describes this engine control structure, which is specifically developed for the lean-burn CNG engine. In the second part, the effects of pre-chamber scavenging on engine performance criteria such as the combustion stability, engine efficiency or engine emissions are analyzed. With the objective to use pre-chamber scavenging to improve engine performance, a scavenging feed-back control strategy is proposed. In order to control the ignition delay, this strategy adapts the amount of CNG injected into the pre-chamber with a linear controller or an extremum seeking algorithm depending on the air-to-fuel ratio of the main chamber.