Pre-combustion Chamber Research Articles

Ignition processes and characteristics of charring conductive polymers with a cavity geometry in precombustion chamber for applications in micro/nano satellite hybrid rocket motors

The arc ignition system based on charring polymers has advantages of simple structure, low ignition power consumption and multiple ignitions, which bringing it broadly application prospect in hybrid propulsion system of micro/nano satellite. However, charring polymers alone need a relatively high input voltage to achieve pyrolysis and ignition, which increases the burden and cost of the power system of micro/nano satellite in practical application. Adding conductive substance into charring polymers can effectively decrease the conducting voltage which can realize low voltage and low power consumption repeated ignition of arc ignition system. In this paper, a charring conductive polymer ignition grain with a cavity geometry in precombustion chamber, which is composed of PLA and multiwall carbon nanotubes (MWCNT) was proposed. The detailed ignition processes were analyzed and two different ignition mechanisms in the cavity of charring conductive polymers were revealed. The ignition characteristics of charring conductive polymers were also investigated at different input voltages, ignition grain structures, ignition locations and injection schemes in a visual ignition combustor. The results demonstrated that the ignition delay and external energy required for ignition were inversely correlated with the voltages applied to ignition grain. Moreover, the incremental depth of cavity shortened the ignition delay and external energy required for ignition while accelerated the propagation of flame. As the depth of cavity increased from 2 to 6 mm (at 50 V), the time of flame propagating out of ignition grain changed from 235.6 to 108 ms, and values of mean ignition delay time and mean external energy required for ignition decreased from 462.8 to 320 ms and 16.2 to 10.75 J, respectively. The rear side of the cavity was the ideal ignition position which had a shorter ignition delay and a faster flame propagation speed in comparison to other ignition positions. Compared to direct injection scheme, swirling injection provided a more favorable flow field environment in the cavity, which was beneficial to ignition and initial flame propagation, but the ignition position needed to be away from the outlet of swirling injector. At last, the repeated ignition characteristic of charring conductive polymers was also investigated. The ignition delay time and external energy required for ignition decreased with repeated ignition times but the variation was decreasing gradually.

Study on Slagging Characteristics of Boiler Pre-combustion Chambers Based on Deep Learning.

The pre-combustion chamber (PCC) is commonly used to ensure stable combustion in boilers. However, when a coal-fired boiler uses a PCC combustor, the cross-sectional area and volumetric heat load in the PCC are high, which is prone to slagging, affecting the safe and stable operation of the boiler. Therefore, developing a fast and accurate prediction model is very important for judging the degree of slagging on the wall of the PCC. In recent years, artificial intelligence (AI) has been widely used in the field of thermal engineering, especially in the prediction of slagging. However, currently, using neural networks to predict the degree of boiler slagging only inputs simple parameters such as silicon ratio and acid-base ratio, without considering the actual complex flow and combustion characteristics in the furnace. In order to improve the accuracy of boiler slagging prediction, a deep parallel residual convolution neural network (DPRCNN) is proposed for automatically identifying three types of boiler wall slagging degrees. First, we simulate the boiler combustion process under various operating and structural parameters and output a dataset. Second, experimental validation is used to numerically simulate typical operating conditions, verifying the accuracy of the resulting dataset, and the generated dataset is sent to the DPRCNN model for identification. Finally, a convolutional neural network incorporating parallel thinking is proposed to predict boiler slagging. The experimental results show that the accuracy, accuracy, and area under curve (AUC) of DPRCNN reach 100%, 100%, and 100%, verifying the applicability of deep learning technology to boiler slagging prediction.

Effect of spark timing on the pre-chamber jet ignition in a lean-burn natural gas engine

An enhanced combustion concept, pre-chamber jet ignition can provide high ignition energy and a wide dispersion of ignition sources, thus improving combustion performance and realizing stable lean combustion. However, the ignition performance of the pre-chamber jets depends strongly on the pre-chamber combustion process and is sensitive to many factors. Therefore, this paper will explore the impact of spark timing on the pre-chamber combustion, turbulent jet characteristics, and main chamber combustion performance by CFD simulation based on an active pre-chamber natural gas engine. The in-cylinder flow and combustion processes of the engine are calculated with the fuel-air equivalence ratio of the main chamber maintained at 0.5, and the spark timing varied from 684°CA to 708°CA with a step of 3°CA (compression top dead center is 720°CA). The results show that, in the present engine operating point, the pre-chamber combustion heat release rate is improved when the spark timing is retarded from 696°CA to 705°CA, and the injection velocity of the pre-chamber jet accordingly increases. As the spark timing continues to be delayed until 708°CA, the pre-chamber combustion deteriorates, and the injection velocity of the pre-chamber jet decreases. Under the combustion phase CA50 no more than 725°CA and the combustion duration CA5-90 fixed around 30°CA, the IMEP will maintain a relatively stable value when the spark timing is delayed from 693°CA to 705°CA, in the meantime, the NOx emission decreases with the delay of spark timing. Therefore, on the premise of ensuring engine power performance, it is a feasible scheme to delay spark timing to reduce NOx emission for the natural gas engine with an active pre-chamber.

Numerical simulation of lean premixed combustion characteristics and emissions of natural gas-ammonia dual-fuel marine engine with the pre-chamber ignition system

As an efficient hydrogen carrier, ammonia (NH3) has great potential to realize the target of carbon neutralization. In this paper, a natural gas-ammonia dual-fuel engine model has been established to evaluate the feasibility of ammonia application in a high-pressure medium-speed four-stroke natural gas marine engine. In order to achieve the efficient and clean combustion of ammonia, a method combining the pre-chamber ignition system with lean-burn combustion technology was proposed. In addition, a CH4/NH3 combustion mechanism with reasonable accuracy was developed to simulate the combustion process of the engine. Moreover, the effect of using various ammonia concentration in the fuel on jet flame formation, thermal efficiency, unburned ammonia, and NOx and N2O emissions were compared. The results showed that the pyrolysis of ammonia mixtures in the pre-combustion chamber promoted the formation of jet flame, which had a “chain effect” on the turbulent kinetic energy in the main combustion chamber and further enhanced the flame propagation in lean conditions. In addition, NOx emission showed a decreasing function of the split ratio of ammonia, which was caused by the NO reduction by unburned NH3. However, the low-temperature generation characteristics of N2O emissions led to the opposite trend. Furthermore, the application of ammonia increased N2O emissions by 0.18–0.49 g/kWh, which is about 0.06%–0.1% of nitrogen in ammonia fuel, resulting in a partial offset of CO2 emission reduction effect.

Flame Dynamics in the Combustion Chamber of Hybrid Rocket Using Multiangle Chemiluminescence

The flame dynamics in the combustion chamber of a hybrid rocket motor were visualized using novel chemiluminescence imaging. A multidirectional visualization system employing endoscopes generated images based on methylidyne chemiluminescence (CH*), with one endoscope in the precombustion chamber and two in the postcombustion chamber. Images were collected with a high-speed camera using a 1 ms exposure and a 1 kHz frame rate. Fuel grains having a helical or a conventional circular port structures were assessed, and combustion trials were conducted using a laboratory-scale hybrid rocket motor with oxygen as the oxidizer at mass flow rates from 10.43 to : equivalent to combustion chamber pressures ranging from 0.7 to 1.24 MPa. Flame structures were observed during the ignition, combustion, and shutdown stages; and the helical grain generated a larger, more intense flame zone. A proper orthogonal decomposition analysis showed that the helical grains also produced a greater degree of turbulence and stronger oscillations. These results confirm that a helical structure increases the flow turbulence and convective heat transfer in the combustion chamber. These effects lead to higher regression rates and better mixing efficiency that may, in turn, provide greater combustion efficiency at optimized oxidizer/fuel ratios.

Computational assessment of the effects of pre-chamber and piston geometries on the combustion characteristics of an optical pre-chamber engine

Pre-chamber combustion (PCC) has the potential to extend the lean-burn limit in spark-ignition engines, which can promote engine efficiency and relieve the concern of emissions of nitrogen oxides. This work assessed the effects of pre-chamber (PC) and piston geometries on the combustion characteristics of an optical methane PCC engine with both experimental and computational approaches. Five active-type PCs with different volumes and nozzle diameters (12 nozzles distributed evenly in two layers) and two pistons (bowl and flat) were tested under lean-burn conditions. Multi-cycle pressure and heat release profiles, natural flame luminosity images, and OH* chemiluminescence images were measured and employed for CFD modeling validations. The PCs with the smaller nozzle diameter yielded more intensely-reacting jets from the upper layer of nozzles compared to the other PCs, attributed to the stronger gas choke there, which dramatically affected the flow fields. A larger PC volume allowed more air–fuel mixture to be trapped within the PC whose combustion then resulted in faster pressure buildup, which, however, led to higher heat transfer loss. Compared to the bowl piston, the flat piston generated a higher heat release rate during the late combustion period owing to the relatively longer jet propagation within the squish region.

Analysis of micro-mixing and chemical kinetic effects of ultra-lean methane-air mixture ignited by turbulent jets

The Equilibrium-PaSR and the Constant-volume reactor framework were used to construct the TJI combustion system with or without turbulence effects. Numerical investigations on micro-mixing and chemical kinetic effects of ultra-lean methane-air mixture ignited by turbulent jets were conducted. The results show that main chamber combustion (MCC) is commonly affected by the jet reactive stages and fuel mixed time. The higher mixing time leads to faster heat transfer and less temperature rise, which ultimately limits the fuel conversion. So PaSR1 fuel reactivity has a stronger effect on t50 (time of 50 % fuel conversion in MCC) than the micro-mixing effect. Besides, the methane content in the jet is particularly important for the overall combustion process in MCC. For the analysis of the chemical kinetic effects, it is known that the ignition of MCC at lower temperatures is more strongly affected by the chemical effects of the combustion products from the pre-combustion chamber (PCC). As the temperature increases, the chemical effect decreases slightly, and the physical effect presents an increasing trend. The low-carbon intermediate CH3/C2H2 radicals in the cold jet have the most significant effect on shortening the ignition delay time (IDT). The ignition ability of the hot jet is closely related to the chemical effects of H/O/OH radicals, and the chemical effects of important low-carbon intermediate species are significantly reduced. For flame instability analysis, the combustion products can reduce the flame thickness of the mixture in MCC to increase the intensity of hydrodynamic instability. With the increase of [O + OH], the destabilizing effect of the thermal-diffusion instability of methane-air premixing gradually increases.

Numerical study of slagging trends in the pre-combustion chamber at swirl-burner outlet under different secondary-air temperatures

• The slagging trend of the PCC wall at different T SA is predicted by CFD. • The temperature near the PCC wall increases with increasing T SA . • The relationship between the T SA and slagging trend of the PCCwall is established. • Low T SA is better for protecting the PCC wall from slagging. The swirl burner with the pre-combustion chamber (PCC) has good combustion stability and is usually used in industrial pulverized coal boilers (IPCBs). Due to the limited space of PCC, it is easy to cause slagging on the wall, which affects the operation of the boiler. For different IPCBs, the designed secondary-air temperature ( T SA ) varies widely. Some boilers use outdoor air as SA, thus the T SA is low; other boilers use the air heated by the air preheater as SA, thus the T SA is high. Importantly, the slagging characteristics under different design temperatures are quite different. Hence, for the safe operation of boilers, it is necessary to study the slagging characteristics of PCC walls under different designed T SA , which in turn provides a reference for the design of T SA in IPCBs. In this paper, based on a 29 MW IPCB, the influence of T SA on slagging trends in the PCC is studied by CFD. The relationship between T SA and the slagging trend of PCC walls is established. The higher the T SA , the greater the intensity of pulverized coal combustion, which is more conducive to pulverized coal burnout; meanwhile, the temperature near the PCC wall rises, resulting in the slagging trend increases. This is inconsistent with the results of studies on slagging at burner outlets in coal-fired utility boilers. When T SA is 485K, the slagging trend is about 540 times more serious than that when T SA is 385K. The results of this paper show that the designed T SA should be reduced as much as possible, which is more conducive to protecting the PCC from slagging.

Pre-Chamber Combustion Model for Pre-Chamber Gas Engine

Pre-Chamber Combustion Model for Pre-Chamber Gas Engine

Optical evaluation of orifice orientation and number effects on active pre-chamber spark ignition combustion

Pre-chamber spark ignition combustion has shown several advantages for its implementation in engines, mainly related to its capability to achieve stable operation at lean or diluted mixtures and increased combustion speed. However, such systems have two challenges compared to traditional spark-ignition combustion: on the one hand, the stratification of the combustion process implies the usage of advanced tools for the analysis and optimization of the combustion system; on the other hand, the ignition process and overall combustion development is very sensitive to variations in the pre-chamber geometry. Previous works have explored particularly the effects of the pre-chamber volume compared to the engine displacement, the relationship between this volume and the total flow area of the nozzle connecting it to the rest of the cylinder, as well as the number and distribution of the nozzle orifices. In this work, the effect of the orientation of such orifices is explored on an optically-accessible rapid compression-expansion machine. Two main configurations are used: straight nozzle, where the axes of all the orifices intersect in a single point approximately in the center of the pre-chamber volume; and tilted nozzle, where the axes of two opposed orifices are displaced 1.5 mm, inducing a swirling motion both in the pre-chamber during the compression process and in the main chamber once ejection starts. Additionally, a sensitivity to the number of orifices is performed for the tilted nozzle layout. The results show that the induced swirling motion has little effect on the pre-chamber combustion development and initial ejection velocity, but it has a positive impact on the subsequent flame propagation and combustion efficiency, especially for ultra-lean conditions.

Effect of mixing section configurations on combustion efficiency of Mg-CO2 Martian ramjet

Experiments were conducted to determine the effects of the mixing section configurations on the Mg-CO2 Martian ramjet combustion efficiency. It was carried out at a mainstream mass flow rate of 110 g/s and a temperature of 810 K. The chamber pressure was measured under different configurations and Oxidizer to Fuel (O/F) ratios. Results showed that the engine achieved self-sustaining combustion and worked stably during experiments. The pre-combustion chamber is needed to increase the combustion efficiency and promote the full combustion of the powder. After the configuration of the pre-combustion chamber, the best combustion efficiency reached 80% when radial powder injection and lateral carbon dioxide intake were used. In addition, the O/F ratio in the pre-combustion chamber decreased from 0.67 to 0.31, resulting in an 8% increase in the combustion efficiency. It was speculated that different mixing section configurations and the variations in an O/F ratio within the pre-combustion chamber impacted the combustion efficiency and in essence, all affected the flow velocity and residence time of the two-phase flow in the combustion chamber.

Hydrogen pre-chamber combustion at lean-burn conditions on a heavy-duty diesel engine: A computational study

The combustion of hydrogen generates almost no harmful emissions except for nitric oxides (NOx), which could be effectively eliminated under lean-burn conditions. In particular, the pre-chamber combustion concept has the potential to further extend the lean-burn limit. To pursue a sustainable mode of the powertrain in future transportation, this work intended to investigate the hydrogen pre-chamber combustion concept on a heavy-duty diesel metal engine under lean-burn conditions. By using the CFD modeling method, the pathway to achieving higher engine efficiency along with lower NOx emissions were explored. The results demonstrated that the lean-burn passive pre-chamber combustion effectively restrained the heat release process within the pre-chamber and yielded negligible NOx emissions while degrading complete combustion and combustion stability as a trade-off. To extend the engine operating range, an adequate amount of fuel was introduced into the pre-chamber. Compared to methane, the active pre-chamber combustion of hydrogen exhibited a significantly higher tendency to induce end-gas autoignition owing to its faster heat release within the pre-chamber. The pressure rise rate within the pre-chamber was successfully controlled by adjusting the pre-chamber throat diameter. Higher thermal efficiency was achieved with an increased compression ratio at the same spark ignition timing because of the advanced combustion phasing. However, the operating range was narrowed for the limit of end-gas autoignition and high pressure rise rate.

Comparative Study of Spark-Ignited and Pre-Chamber Hydrogen-Fueled Engine: A Computational Approach

Hydrogen is a promising future fuel to enable the transition of transportation sector toward carbon neutrality. The direct utilization of H2 in internal combustion engines (ICEs) faces three major challenges: high NOx emissions, severe pressure rise rates, and pre-ignition at mid to high loads. In this study, the potential of H2 combustion in a truck-size engine operated in spark ignition (SI) and pre-chamber (PC) mode was investigated. To mitigate the high pressure rise rate with the SI configuration, the effects of three primary parameters on the engine combustion performance and NOx emissions were evaluated, including the compression ratio (CR), the air–fuel ratio, and the spark timing. In the simulations, the severity of the pressure rise was evaluated based on the maximum pressure rise rate (MPRR). Lower compression ratios were assessed as a means to mitigate the auto-ignition while enabling a wider range of engine operation. The study showed that by lowering CR from 16.5:1 to 12.5:1, an indicated thermal efficiency of 47.5% can be achieved at 9.4 bar indicated mean effective pressure (IMEP) conditions. Aiming to restrain the auto-ignition while maintaining good efficiency, growth in λ was examined under different CRs. The simulated data suggested that higher CRs require a higher λ, and due to practical limitations of the boosting system, λ at 4.0 was set as the limit. At a fixed spark timing, using a CR of 13.5 combined with λ at 3.33 resulted in an indicated thermal efficiency of 48.6%. It was found that under such lean conditions, the exhaust losses were high. Thus, advancing the spark time was assessed as a possible solution. The results demonstrated the advantages of advancing the spark time where an indicated thermal efficiency exceeding 50% was achieved while maintaining a very low NOx level. Finally, the optimized case in the SI mode was used to investigate the effect of using the PC. For the current design of the PC, the results indicated that even though the mixture is lean, the flame speed of H2 is sufficiently high to burn the lean charge without using a PC. In addition, the PC design used in the current work induced a high MPRR inside the PC and MC, leading to an increased tendency to engine knock. The operation with PC also increased the heat transfer losses in the MC, leading to lower thermal efficiency compared to the SI mode. Consequently, the PC combustion mode needs further optimizations to be employed in hydrogen engine applications.

Study on the slagging trends of the pre-combustion chamber in industrial pulverized coal boiler under different excess air coefficients by CFD numerical simulation

Industrial pulverized coal boiler (IPCB) usually employ a pre-combustion chamber (PCC) to ensure stable combustion. However, there are potential slagging problems in the PCC, which threaten the safe operation of the boiler. Air-staged combustion technology is an effective method to reduce NOx emission, and different excess air coefficients affect slagging. CFD simulation is an important method for studying slagging in the furnace. In this paper, Using CFD simulation with slagging model embedded by user-defined function, the slagging trends in the PCC are studied under different excess air coefficients. The particles' collision rate (CR), deposition rate (DR), and sticking rate (SR) on the PCC walls are obtained by CFD simulation. As the excess air coefficient in the PCC (αPCC) increases from 0.3 to 1.1, the CR of particles on all walls of PCC (CRPCC) increases exponentially, indicating the abrasion degree on the PCC walls is growing rapidly. In addition, due to the sizeable annular recirculation zone when αPCC = 0.3, the DR of particles on all walls of PCC (DRPCC) and the SR of particles on all walls of PCC (SRPCC) are much larger than those under other conditions, the slagging trend is the worse. As the αPCC increases from 0.3 to 1.1, the slagging trends in the PCC first decrease and then increase. To improve the safety of boiler operation, it is recommended that the αPCC be adjusted between 0.5 and 0.9.

Dynamic Numerical Simulation of Hybrid Rocket Motor with HTPB-Based Fuel with 58% Aluminum Additives

The addition of aluminum (Al) to the fuel is an effective way to increase the regression rate of hybrid rocket motors (HRMs). Due to its high regression rate, the impact of the regression of combustion surface on the performance of HRMs cannot be ignored. Therefore, it is significant to establish a dynamic numerical simulation model to predict the performance of HRMs. In this study, the dynamic simulation model was established based on dynamic mesh technology and was verified by a firing test. The results show that the simulation results agree well with the experimental results, and the errors of the average thrust and combustion chamber pressure are 3.4% and 1.4%, respectively. The dynamic simulation shows that with the regression of the combustion surface, the vortex of the pre-combustion chamber is divided into two vortices. The vortex near the front of the grain will increase the regression rate downstream. The results show that the addition of Al can obviously improve the regression rate of HRMs. The fuel containing 58% Al can improve the regression rate by 88.8% compared with the fuel with pure hydroxyl-terminated polybutadiene (HTPB). Moreover, due to the higher combustion temperature and the scouring of metal particles, the ablation rate of the nozzle with carbon ceramic materials reaches 0.16 mm/s. This investigation provides a valuable reference for HRMs design and simulation.

The effect of structural parameters of pre-chamber with turbulent jet ignition system on combustion characteristics of methanol-air pre-mixture

Pre-chamber turbulent jet ignition technology is an effective way to optimize the methanol-air mixture combustion process. A literature survey of structures of currently used pre-chambers of turbulent jet ignition systems was conducted, and three levels of four key structural factors were extracted from them, and nine pre-chambers were redesigned using the Taguchi experimental design method. The test showed that there are four typical pre-chamber ignition modes in the methanol-air mixture, namely, jet flame ignition, jet ignition, jet wake ignition, and dual-jet ignition. Compared with a spark plug, these ignition modes can increase the peak heat release rate by 15.78%, 123.51%, 136.96%, and 235.19%, respectively. When the mixture concentration in the pre-chamber is stoichiometric, the lean-burn limit for jet ignition and jet wake ignition is similar to that for spark ignition. By contrast, jet flame ignition can significantly extend the lean-burn limit. Among all the pre-chamber structural parameters, the total cross-sectional area of ​​the nozzles influenced the pre-chamber combustion performance and lean-burn limit performance the most, and the weight of the influence was always greater than 80%. The effects of the transition angle in the pre-chamber, the throat diameter, and the number of nozzles on its performance are discussed in this paper.

A computational assessment of flame speed correlation in an ultra-lean pre-chamber engine

Predictive modeling of pre-chamber combustion engines relies primarily on the correct description of laminar and turbulent flame speeds. For engineering applications, the correlations of the flame speeds with physical variables involve empirical constants that are valid for a limited range of operating conditions. The current work aims at assessing the significance of laminar flame speed prediction in the simulation of ultra-lean pre-chamber engine combustion operated with methane. Gülder’s empirical correlation for laminar flame speed was chosen as a reference and was further modified for equivalence ratio, pressure and temperature ranges beyond what it was originally derived for, in order to confirm the original hypothesis; the pressure and temperature dependence were adopted as a power-law correlation. Based on the computational results using the skeletal reaction mechanism, the correlation was modified better represent the flame speeds at ultra-lean engine conditions, using GRI 3.0 as a reference. The modified correlation for methane was implemented in CONVERGE, a three-dimensional computational fluid dynamics (CFD) solver, and the results were validated against the experimental data. In all cases, the original formulation of Peters’s turbulent flame speed correlation was used and was found to have insignificant effect on the conditions under study, confirming the importance of the accurate determination of the laminar flame speed that dominates over any turbulence corrections for high Karlovitz number effects. The flame topology was also investigated to provide insights into the observed pressure behavior among the tested cases. Finally, the relevant turbulent combustion regimes encountered in the pre-chamber combustion engine conditions were examined in the Borghi-Peters diagram, further confirming the findings of the study.

Performance of a Solid-Fuel Ramjet Combustor with Bypass Air Addition

The influence of bypass air addition on the performance of a solid-fuel ramjet combustor was investigated. Experiments were performed with cylindrical center-perforated hydroxyl-terminated polybutadiene fuel grains and unvitiated heated air at flight-relevant pre-ignition combustor inlet total temperatures. The core air mass flow rate was kept constant, whereas the bypass ratio was varied from 0 to 30% with consistent pre-combustion chamber pressures. The average regression rate and mass flow rate of the fuel were greatest for the 0% bypass ratio case. The regression rate decreased for the 30% bypass ratio and for cases in which carbon black was not added to the fuel grain. Increasing the mass flow rate of air bypassed to the secondary combustion zone reduced the overall chamber pressure. The thrust increased with the increasing bypass ratio. The effect of bypass air on the chamber pressure yielded lower characteristic velocities at the 30% bypass ratio than at the 0 and 15% bypass ratios. The combustion efficiency of the device was maximized for the 15% bypass ratio. The key outcomes of the bypass air addition are to lower the global equivalence ratio and to reduce the combustion chamber pressure such that there is a nonzero bypass ratio for which the combustion efficiency is maximized.

Investigations on an active pre-chamber ignition system in a combustion chamber

Pre-chamber ignition systems are one way to enable homogeneous lean or dilute combustion. Both strategies can significantly increase the efficiency of spark ignition engines. Spark initiated combustion in the pre-chamber produces hot gases that rapidly enter the cylinder and ignite the diluted charge at multiple points. Active ignition systems with fuel in the pre-chamber can directly influence the composition of the pre-chamber to ensure good ignition properties and sufficient ignition energy. This paper shows results from a novel test facility that enables investigations on the jet propagation of an active pre-chamber inside a constant pressure vessel. Thereby, the background mixture inside the vessel is variated between λ = 1.0 and λ = 2.0. With a special designed single-hole pre-chamber the flame propagation of a single pre-chamber jet is measured both in direction of the transfer port and perpendicular to this direction. Compared to spark ignition under equal ambient conditions (350°C, 10 bar), the pre-chamber combustion propagates around eight times faster in direction of the transfer port and 60% faster in radial direction. Until λ = 1.6, the flame propagation speed in radial direction can be kept on the level of a stoichiometric spark ignition. The simultaneous record of OH*-chemiluminescence and high-speed Schlieren imaging shows that the dominant ignition mechanism of a passenger-car sized pre-chamber is jet ignition according to the classification of Biswas. In stoichiometric cylinder conditions, a rich pre-chamber hampers the ignition in the main chamber whereas in lean operation points the scavenging of the pre-chamber with a rich λ = 0.8 mixture is beneficial. These measurements indicate how the disrupted flame front of a pre-chamber jet increases the turbulence and enhances the flame propagation. The highest recorded propagation speed occurs in stoichiometric conditions both in the pre-chamber and in the combustion module.

Jet Characteristics of a Narrow Throat Pre-Chamber and Influence on the Main-Chamber Combustion

<div class="section abstract"><div class="htmlview paragraph">Lean combustion is one of the most applied methods to increase engine efficiency and maintain a good trade-off with engine emissions. The pre-chamber combustion (PCC) is one of the most promising combustion concepts to extend the lean operating limits of the engine. The Narrow throat pre-chamber has shown better lean limit extension compared to other ignition sources. The pre-chamber jets and the main-chamber combustion were studied in a Heavy-Duty optical engine using methane fuel. The tested conditions covered global excess air ratios (λ), between 1.9 to 2.3. The combustion process was recorded using three collection systems: (a) Natural Flame Luminosity (NFL) with a temporal resolution of 0.1 CAD; (b) OH* Chemiluminescence, and (c) CH* Chemiluminescence with a temporal resolution of 0.2 CAD for both. The propagating velocity of the reacting jets was studied using Combustion Image Velocimetry (CIV) based on bottom view images of the main chamber. After the pre-chamber jets ignite the main-chamber charge, a two-stage heat release rate (HRR) was observed for all the tested conditions. None of the three combustion visualizations exhibited a linear correlation with the HRR. The CIV reported high-speed jets penetrating around 400 m/s into the main chamber. The richest case of λ 1.9 presented a higher axial and radial propagation speed than the other cases. The individual vector fields have significant differences with the ensemble average fields, behavior characteristic of a high turbulent process. Finally, the ultra-lean case showed higher vorticity during the pre-chamber discharge, a synonym of high air-fuel entrainment that generates heavy waviness on the flame front. This heavy waviness generates local/partial or total extinction, resulting in abnormal combustion cycles.</div></div>