Pre-chamber Jet Ignition Research Articles

Visualization study on the effects of pre-chamber jet ignition and methane addition on the combustion characteristics of ammonia/air mixtures

As a carbon-free green fuel, ammonia has recently attracted more and more attention. However, the application of ammonia as an alternative fuel in internal combustion engines is a challenge due to its low chemical reactivity. Thus, more fundamental researches on the combustion characteristics of ammonia are necessary to enhance the ignition and combustion of ammonia in internal combustion engines. In this study, the effects of pre-chamber jet ignition and different methane additions on the combustion characteristics of ammonia/air mixtures were investigated experimentally. The experimental results showed that pre-chamber jet ignition could improve the combustion performance of the premixed ammonia/air and ensure combustion stability at a low equivalence ratio, compared with spark direct ignition. For the jet ignition mode, the optimal equivalence ratio of the ammonia/air mixtures was between 1.0 and 1.1. The combustion duration was determined by the flame transverse propagation velocity, which was minimally influenced by the jet flame. For both jet ignition and direct ignition modes, a higher initial pressure would hinder the flame propagation resulting in a longer combustion duration, while an increase in the maximum pressure led to an increase in the average pressure rise rate. And for both ignition modes, the promotion of increasing methane addition from 0 to 10% on the pure ammonia combustion was higher than that of increasing methane addition from 10% to 20% on the combustion, and small amounts (10% and 20%) of methane addition had a less promotion on pure ammonia combustion at a higher initial pressure.

Effects of Cooled Exhaust Gas Recirculation Combined With Prechamber Jet Ignition on the Combustion Characteristics in a Kerosene-Fueled Spark Ignition Engine

Abstract For security and logistical convenience, the single fuel forward policy hopes to use a single kerosene fuel to replace a variety of military fuels, especially the unsafe gasoline. However, the performance of kerosene-fueled spark ignition (SI) engines is severely restricted by knock, slow combustion rate, and poor combustion stability. This work innovatively applies cooled exhaust gas recirculation (EGR) combined with prechamber jet ignition (PJI) to a kerosene-fueled engine to suppress knock and improve performance. The results show that applying cooled EGR at a fixed throttle opening can suppress knock and improve fuel economy. However, the power decreased due to the decreased intake of energy. While applying EGR with constant fresh air mass flow makes the knock more prominent because of the microboosting effect caused by the increased throttle opening. This indicates that cooled EGR alone cannot improve the power output. Moreover, combustion instability was also caused due to the slower combustion rate. Therefore, PJI was introduced to compensate for the negative impact of EGR. As a result, a synergistic effect of cooled EGR and PJI was discovered, improving the IMEP by 5% and reducing the ISFC by 4.9% compared to the baseline. The PJI can shorten the combustion duration and improve the combustion stability because of the high kinetic energy jet and high turbulence flame. In addition, a novel two-stage heat release process which includes the unusual first-stage low-temperature heat release was discovered. Overall, EGR dominates the knock suppression, and PJI contributes to the combustion rate improvement.

Experimental Study of the Effects of Pre-Chamber Geometry on the Combustion Characteristics of an Ammonia/Air Pre-Mixture Ignited by a Jet Flame

In the future, ammonia is expected to become a carbon-free fuel for internal combustion engines. However, the flammability of ammonia is poorer compared to conventional fuels such as gasoline and diesel fuel. Pre-chamber jet ignition may be an effective way to ensure stable ignition and enhance the combustion of ammonia. In this paper, the effects of pre-chamber geometric parameters, including volume and orifice diameter, on the jet ignition and combustion processes were studied using visualization methods, combined with pressure acquisition. The results showed that ignition energy increased and the jet duration was prolonged with the increase in pre-chamber volume, resulting in a higher maximum pressure and pressure rise rate in the main chamber. The jet characteristics of a larger volume pre-chamber exhibited higher stability when the ambient parameters were changed. The smaller volume pre-chamber showed the superiority of a shorter flame propagation distance inside the pre-chamber, which advanced the timing of the jet appearance and shortened the ignition delay when the flammability of the pre-mixture was adequate. The larger pre-chamber orifice diameter caused an earlier jet ignition timing, shorter ignition delay, and higher ignition location. The jet duration for the pre-chamber with a smaller orifice was longer, which was beneficial for increasing the pressure rise rate in the main chamber. Too small a pre-chamber orifice led to ignition failure in the main chamber.

Effects of Orifice Diameter of Pre-Chamber Jet Ignition on the Combustion Characteristics and Pressure Oscillations in a Kerosene-Fueled Engine

Abstract Jet orifice diameter directly impacts the combustion process of the pre-chamber jet ignition (PJI) engine and the optimized diameter is varied with the fuel properties. However, research on the optimization of the jet orifice diameter based on aviation kerosene fuel has not been reported. So, this paper investigates the effect of orifice diameter on combustion, pressure oscillation, and performance based on a kerosene-fueled single-cylinder test engine. Two pressure sensors are respectively fitted in the main combustion chamber and the pre-chamber, which can capture the pressure change process and pressure oscillations phenomenon at the two positions, respectively. The result demonstrates that the throttling of the jet orifice leads to a significant three-stage pressure imbalance between the combustion chambers. With the reduction of the orifice diameter, the combustion acceleration of PJI is enhanced, resulting in an advanced combustion phase, improved combustion stability, and enhanced knock. The time-frequency analysis proves that the pressure oscillation propagation to the pre-chamber is frequency-selective and related to the orifice diameter. By matching the pre-chamber Helmholtz resonance frequency with the main chamber resonance frequency, strong pressure oscillations can be excited in the pre-chamber. Meanwhile, the pressure oscillation energy can be absorbed by the pre-chamber, which may help reduce the engine's combustion noise. Moreover, the PJI with an orifice diameter between 2 mm and 4 mm can improve the combustion stability with the ISFC reduced by 4.7–5.6%, and the IMEP increased by 1.2–2.6%.

Lean combustion and emission performance of a gasoline direct injection engine with active pre-chamber

Pre-chamber jet ignition technology can effectively improve flame propagation speed and in-cylinder combustion rate, so it is conducive to the improvement of thermal efficiency and fuel economy. While, studies on the key parameters of the influence of active pre-chamber on combustion and emissions are not systematic. The influence of the key parameters of injection control in active pre-chamber on combustion and emission is not clear at present. Thus, in this paper, an active pre-chamber jet ignition system was designed and used in a single cylinder GDI engine, and the effects of compression ratio and pre-chamber injection strategy on pre-chamber jet ignition were experimentally studied, as well as the comparison of pre-chamber jet ignition and conventional spark ignition. The results show that, at 2750 r/min, IMEP 11 bar operation point, lean burn can effectively reduce the fuel consumption and increase the thermal efficiency of gasoline engine. Adopting traditional spark plug system can extend the lean burn limit to excess air ratio of 1.5 with the gross indicated thermal efficiency (GITE) of 45% limited by unstable combustion, while resembling active pre-chamber system can achieve GITE of 46.5% with the excess air ratio of 2.0 with the help of much more stable combustion. And the NOx emission of active-pre-chamber system has been reduced by 78% compared by conventional spark plug system. Increasing the compression ratio to 14.8 can further reduce the indicated fuel consumption to 177 g/kWh, and increase the GITE to 48.5% and further reduce the NOx emission to lowest 0.53 g/kWh with the excess air ratio of 2.1. With the increase of pre-chamber injection pressure, the ignition stability increases, the combustion duration decrases, and thermal efficiency increases. With the increase of the pre-chamber injection duration, the ignition delay first decreases and then increases. When the injection duration increases to 800 μs, COV is greater than 3%. If the pre-chamber injection duration further increase, the COV increases, the combustion phasing retard, and the thermal efficiency decreases. With the increase of pre-chamber injection duration and pressure, the wetting wall fuel increases, which leads to the increase of PN emission.

Experimental study of aviation kerosene engine with PJI system

The spark-ignition (SI) piston engine has become the main power source for unmanned aerial vehicles owing to its small size and large power/weight ratio. While gasoline is the commonly used fuel in SI engines, it affords poor safety and stability. Aviation kerosene is highly suitable as an alternative to gasoline; however, its high kinematic viscosity and low saturated vapour pressure afford poor evaporation and atomisation in SI engine. Moreover, aviation kerosene has a low octane number, and easy to cause knock, particularly in four-stroke engines. Those issue limits the wide use of kerosene in SI engines. In this study, the pre-chamber jet ignition (PJI) technology is used to suppress the knock of kerosene engine. The combustion characteristics of gasoline-SI, kerosene-SI and kerosene-PJI were compared and analysed. The variation law of indicated mean effective pressure (IMEP) at different speeds is obtained. It is found that PJI system can accelerate the flame propagation speed and shorten the combustion duration, and IMEP can be increased by 10%–27%. The experimental results show that PJI can optimise kerosene combustion to a certain extent and broaden its knock limit in SI engine. It is one of the effective ways to suppress knock in kerosene engine.

Effects of passive pre-chamber jet ignition on combustion and emission at gasoline engine

Pre-chamber jet ignition is a promising way to improve fuel consumption of gasoline engine. A small volume passive pre-chamber was tested at a 1.5L turbocharged GDI engine. Combustion and emission characteristics of passive pre-chamber at low-speed WOT and part load were studied. Besides, the combustion stability of the passive pre-chamber at idle operation has also been studied. The results show that at 1500 r/min WOT, compared with the traditional spark ignition, the combustion phase of pre-chamber is advanced by 7.1°CA, the effective fuel consumption is reduced by 24 g/kW h, and the maximum pressure rise rate is increased by 0.09 MPa/°CA. The knock tendency can be relieved by pre-chamber ignition. At part load of 2000 r/min, pre-chamber ignition can enhance the combustion process and improve the combustion stability. The fuel consumption of pre-chamber ignition increases slightly at low load, but decreases significantly at high load. Compared with the traditional spark ignition, the NOx emissions of pre-chamber increase significantly, with a maximum increase of about 15%; the HC emissions decrease, and the highest decrease is about 36%. But there is no significant difference in CO emissions between pre-chamber ignition and spark plug ignition. The intake valve opening timing has a significant influence on the pre-chamber combustion stability at idle operation. With the delay of the pre-chamber intake valve opening timing, the CoV is reduced and can be kept within the CoV limit.

Comparison of Excess Air (Lean) vs EGR Diluted Operation in a Pre-Chamber Air/Fuel Scavenged Dual Mode, Turbulent Jet Ignition Engine at High Dilution Rate (~40%)

<div class="section abstract"><div class="htmlview paragraph">Charge dilution is widely considered as one of the leading strategies to realize further improvement in thermal efficiency from current generation spark ignition engines. While dilution with excess air (lean burn operation) provides substantial thermal efficiency benefits, drastically diminished NOx conversion efficiency of the widely used three-way-catalyst (TWC) during off-stoichiometric/lean burn operation makes the lean combustion rather impractical, especially for automotive applications. A more viable alternative to lean operation is the dilution with EGR. The problem with EGR dilution has been the substantially lower dilution tolerance limit with EGR and a consequent drop in thermal efficiency compared to excess air/lean operation. This is particularly applicable to the pre-chamber jet ignition technologies with considerably higher lean burn capabilities but much lower EGR tolerance due to the presence of a high fraction of residuals inside the pre-chamber. Dual Mode, Turbulent Jet Ignition (DM-TJI) technology with its unique ability to work with high external EGR dilution (up to 40% wet/mass basis) due to its additional air delivery to the prechamber offers a viable alternative to the lean burn strategy. DM-TJI could be the technology pathway to realize high EGR diluted combustion with comparable dilution limits to those of the lean burn strategy while still enabling effective use of TWC technology. Present study compares the excess air versus EGR dilution strategy under identical level of dilution (up to 40 %) in a DM-TJI equipped single cylinder engine operating on a high (13.3: 1) compression ratio. The results show that compared to the lean burn operation, EGR dilution provides marginally lower but still comparable thermal efficiency benefits with a marked improvement in NOx reduction, especially in a high compression, knock limited situation. This study showcases that high EGR dilution rates comparable to lean burn operation can be maintained with the DM-TJI system to achieve high thermal efficiency while still operating at stoichiometric air-fuel ratio.</div></div>

Effects of pre-chamber jet ignition on knock and combustion characteristics in a spark ignition engine fueled with kerosene

Pre-chamber jet ignition (PJI) is effective in accelerating combustion, expanding lean combustion limit and improving combustion stability on gas fuel and volatile liquid fuels. However, the effects of PJI on kerosene, which is less volatile and is more prone to knock than gasoline, are rarely discussed. In this work, PJI was applied to ignite kerosene in a direct injection dual spark plugs ignition (DSPI) engine and its effects on knock intensity, knock randomness, heat release rate, combustion phase and combustion stability were studied. Experiments were conducted with compression ratios (CR) of 6 and 7 respectively. Results show that PJI cannot improve the available CR of kerosene. At the early stage of PJI combustion process, a sudden increase and a fluctuation of heat release rate can be observed, which is coincident with the multi point ignition and highly turbulent flame caused by the rapid jet flow. PJI can improve the heat release rate, advance the combustion phase and improve the combustion stability of kerosene, but can also deteriorate the knock intensity without ignition timing adjustment. Due to the improved combustion stability, the randomness of knock is reduced. As a result, advanced combustion phase and reduced knock randomness lead to a better output and fuel consumption performance of PJI under critical knock condition than that of DSPI. The result shows that PJI.

Optical diagnostics on the pre-chamber jet and main chamber ignition in the active pre-chamber combustion (PCC)

We studied the relationship between pre-chamber jet and main chamber ignition in the pre-chamber combustion (PCC) of an optical engine, fueled with methane and equipped with an active pre-chamber with two rows of orifices. Acetone planar laser-induced fluorescence (PLIF) and OH* chemiluminescence imaging techniques were simultaneously applied to visualize the pre-chamber jet and the reaction zone in the main chamber, respectively. The pre-chamber fueling was constant and the main chamber fueling was increased to form an ultra-lean case and a lean case with global excess air ratios (λ) of 2.3 and 1.8, respectively. Results indicate that a higher pressure difference between pre-chamber and main chamber (▵P) produces larger pre-chamber jet penetration speed; the maximum pre-chamber jet penetration speed appears at timing around the peak ▵P. Over enrichment of the pre-chamber charge reduces the peak ▵P and thus does not favor a faster pre-chamber jet discharge. In addition to the main pre-chamber jet, a weaker post jet discharge process is visualized; the former is due to the pre-chamber combustion while the latter due to the ▵P fluctuation and the cylinder volume expansion. The post pre-chamber jet is accompanied by a post reaction zone in the ultra-lean case (λ=2.3) and there are two unburned regions in the main chamber: one is around the pre-chamber nozzle and the other between the adjacent reaction zones. These two unburned regions are consumed by flame propagation in the lean case (λ=1.8). The weak pre-chamber jet from the upper-row orifice does not produce any distinct reaction zone, indicating that the pre-chamber orifice location and arrangement on the nozzle also matters in the pre-chamber design. The pre-chamber jet penetration length is longer than that of the reaction zone during pre-chamber discharge; the penetration length difference between the pre-chamber jet and reaction zone decreases with increasing main chamber fueling.

The Influence of Charge Motion on Pre-Chamber and Main Chamber Combustion in a Highly Dilute Jet Ignition Engine

Though there are multiple viable powertrain options available for the automotive sector, those that contain internal combustion engines will continue to account for the majority of global sales for the next several decades. It is therefore imperative to continue the pursuit of novel combustion concepts that produce efficiency levels significantly higher than those of current engines. Introducing high levels of dilution in spark ignited (SI) engines has consistently proven to produce an efficiency benefit compared to conventional stoichiometric engine operation. However, this combustion mode can present challenges for the ignition system. Pre-chamber jet ignition enables stable, highly dilute combustion by both increasing the ignition energy present in the system and distributing it throughout the combustion chamber. Previous work by the authors have shown that jet ignition produces 15–25% increases in thermal efficiency over baseline SI engines with only relatively minor changes to engine architecture. Lean combustion in general and jet ignition in particular represent fundamentally different engine operating modes compared to those of conventional stoichiometric SI engines. Therefore, there are some system sensitivities not present in stoichiometric engines that must be investigated in order to fully optimize the jet ignition system. Differing types and magnitudes of charge motion are incorporated in SI engines to aid with mixture preparation but the influence of charge motion over lean combustion performance, particularly in jet ignition engines, is less well understood. This study analyzes the impact that charge motion has on both pre-chamber and main chamber combustion. A 1.5 L 3-cylinder gasoline engine is outfitted with multiple intake port configurations producing varying magnitudes and types of charge motion. Pre-chamber and main chamber combustion stability and other burn parameter responses are analyzed across multiple speeds and loads, including at critical operating points such as a catalyst heating condition. The results show that there is combustion sensitivity to charge motion, resulting in >1 percentage point spread in peak thermal efficiency for the configurations tested, and that this sensitivity manifests most significantly under low ignitability conditions such as heavy dilution. These results provide guidance for future system optimization of jet ignition engines.

Study of Pre-chamber Jet Ignition System by Model-based Design

Study of Pre-chamber Jet Ignition System by Model-based Design

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.

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

High-Efficiency and Clean Combustion Natural Gas Engines for Vehicles

Natural gas engines have become increasingly important in transportation applications, especially in the commercial vehicle sector. With increasing demand for high efficiency and low emissions, new technologies must be explored to overcome the performance limitations of natural gas engines such as limits on lean or dilute combustion, unstable combustion, low burning velocity, and high emissions of CH4 and NOx. This paper reviews the progress of research on natural gas engines over recent decades, concentrating on ignition and combustion systems, mixture preparation, the development of different combustion modes, and after-treatment strategies. First, the features, advantages, and disadvantages of natural gas engines are introduced, following which the development of advanced ignition systems, organization of highly turbulent flows, and the preparation of high-reactivity mixtures in spark ignition engines are discussed with a focus on pre-chamber jet ignition, combustion chamber design, and H2-enriched natural gas combustion. Third, the progress in natural gas dual-fuel engines is highlighted, including the exploration of new combustion modes, the development of novel pilot fuels, and the optimization of combustion control strategies. The fourth section discusses after-treatment systems for natural gas engines operating in different combustion modes. Finally, conclusions and future trends in the development of high-efficiency and clean combustion in natural gas engines are summarized.

Experimental study of pre-chamber jet ignition in a rapid compression machine and single-cylinder natural gas engine

Pre-chamber jet ignition is a promising combustion technology to achieve fast combustion in natural gas engines. First, the ignition and combustion characteristics of mixtures in a pre-chamber system with different diameter orifices were studied under engine-relevant pressures and temperatures in a rapid compression machine. The tested fuels, CH4/air stoichiometric mixtures, were diluted by different proportions of CO2/N2 to simulate the corresponding exhaust gas recirculation conditions in engines. High-speed photography was applied to visualize the jet ignition and combustion processes. The experimental results revealed that two ignition patterns existed in the pre-chambers depending on the diameter of orifices. Pre-chamber jet flame ignition pattern appeared when the orifice diameter of the pre-chamber exceeded a critical value, which produced jet flame and ignited the mixtures in the main chamber directly. Pre-chamber jet auto-ignition pattern produced jet which promoted the auto-ignition of mixture in the main chamber when the orifice diameter was smaller and presented much shorter combustion durations. Based on the experimental results in the rapid compression machine, a practical pre-chamber system was designed in a single-cylinder natural gas engine to investigate the combustion performance and emission characteristics. The experimental results indicated appropriate 0.8%–1.4% increases of indicated thermal efficiency were achieved by pre-chamber jet ignition due to the higher combustion efficiency and shorter combustion duration compared to conventional spark ignition. Lower total hydrocarbon and CO emissions but higher NO x emissions were produced by pre-chamber jet ignition due to the faster burning velocity and higher combustion temperature.

Combustion Instabilities of Ultra-Lean Premixed Mixtures by Prechamber Turbulent Jet Ignition

Unstable combustion was observed in a dual-chamber combustor that mimics heavy-duty gas engines utilizing prechamber jet ignition. Prechamber combustion generated a hot turbulent jet that ignited the ultra-lean mixture in the main chamber. Thermoacoustic combustion instability was initiated for main-chamber equivalence ratio, , and grew severe in the lean-burn regime, . Simultaneous schlieren and chemiluminescence were used to visualize the unstable flame propagation and to characterize the instability. Classical acoustic resonator analysis and pressure spectra showed the longitudinal mode of acoustic disturbance as the primary instability mode for all equivalence ratios. However, a leaner flame was affected more due to stronger coupling between heat release and the pressure field perturbation. Transverse and mixed modes were observed at lean conditions, . A phase-resolved measurement of strain rates along flame edge showed an oscillating strain along pressure perturbation cycle. To model the instability, 3D linearized Euler equations were solved in the frequency domain coupled with combustion response models. The physical significance of the instability modes and their behavior were identified using dynamic mode decomposition. Based on the experimental and modeling results, a mechanism for thermoacoustic instability was proposed for ultra-lean premixed ignition by a hot turbulent jet.

A computational study on the effect of the orifice size on the performance of a turbulent jet ignition system

Fully three-dimensional computational fluid dynamic simulations with detailed combustion chemistry of a turbulent jet ignition system installed in a rapid compression machine are presented. The turbulent jet ignition system is a prechamber-initiated combustion system intended to allow lean-burn combustion in spark ignition internal-combustion engines. In the presented configuration, the turbulent jet ignition prechamber has a volume that is 2% of the volume of the main combustion chamber in the rapid compression machine and is separated from the main chamber by a nozzle containing a single orifice. Four simulations with orifice diameters of 1.0 mm, 1.5 mm, 2.0 mm, and 3.0 mm respectively are presented in order to demonstrate the effect of the orifice diameter on the combustion behavior of the turbulent jet ignition process. Data generated by the simulations is shown including combustion chamber pressures, temperature fields, jet velocities and mass fraction burn durations. From the combustion pressure trace, the jet velocity, and other field data, five distinct phases of the turbulent jet ignition process are identified. These phases are called the compression phase, the prechamber combustion initiation phase, the cold jet phase, the hot jet phase, and the flow reversal phase. The four simulations show that the orifice diameter of 1.5 mm provides the fastest ignition and the fastest overall combustion as reflected in the 0–10% and 10–90% mass fraction burn duration data generated. Meanwhile, the simulation for the orifice diameter of 1.0 mm produces the highest jet velocity and has the shortest delay between the spark and the exit of a jet of hot gases into the main chamber but produces a slower burn duration than the simulation for the larger orifice diameter of 1.5 mm. The simulations for orifice diameters of 2.0 mm and 3.0 mm demonstrate that the combustion speed is reduced as the orifice diameter increases above 1.5 mm. Finally, a discussion is given which examines the implications that the results generated have in regard to implementation of the turbulent jet ignition system in an internal-combustion engine.

Modeling unmanned aerial vehicle jet ignition wankel engines with CAE/CFD

The paper presents some details of the CFD modeling of a novel design where jet ignition devices replace the traditional spark plugs for a faster and more complete combustion. The numerical simulations show how the pre-chamber jet ignition in a Wankel engine differs from reciprocating piston engine applications. The jets issuing from the jet ignition pre-chamber have many different speeds in the different directions as the pressure build-up at the trailing edge of the rotating chamber makes extremely fast the ignition of the chamber mixture in the direction of rotation. Conversely it prevents the jet ignition in the opposite direction. Careful positioning along the periphery and design of the connecting pipes and the prechamber volume with the help of CFD simulations permits to achieve extremely fast and complete combustion as impossible with spark plugs. The paper proposes results of CFD simulations of the combustion evolution within a jet ignited Wankel engine rotor, detailing challenges and opportunities of the application, as well as a first assessment of the impact the faster and more complete combustion permitted by jet ignition may have on the performances of Wankel engines for unmanned aerial vehicles applications.

Stochastic reactor modelling of multi modes combustion with diesel direct injection or hydrogen jet ignition start of combustion

Recent papers [1–5] have proposed two different systems to more efficiently and more rapidly burn the fuel in highly boosted, high compression ratio, directly injected internal combustion engines permitting multi-mode combustion operation. In a first system, a second direct injector is coupled with the standard Diesel direct injector and glow plug. The second direct injector introduces the most of the fuel while the Diesel direct injector only introduces a minimum amount of fuel to control the start of the combustion about top dead centre. The fuel injected before the Diesel ignition injection burns premixed, the fuel injected after the Diesel ignition injection burns diffusion. This design permits combustion premixed gasoline-like if all the fuel is injected before the Diesel ignition injection, diffusion Diesel-like if all the fuel is injected after the Diesel ignition injection (as done in the Westport High Pressure Direct Injection concept [12]), and mixed gasoline/Diesel like injecting the fuel before and after the Diesel ignition injection. The premixed gasoline-like mode is actually a homogeneous charge compression ignition (HCCI)-like mode, where an amount of fuel smaller than the threshold value producing top dead centre auto ignition is then ignited at top dead centre by the Diesel ignition injection in a more robust, stable and repeatable operation unaffected by small changes in properties and composition of the fuel and air mixture. In an alternative design, the glow plug is replaced by a jet ignition devices feed preferably with H2. In this case, a spark ignition ignites the stoichiometric H2-air mixture within the jet ignition pre-chamber. The jets of hot reacting H2-air combusting gases then ignite the main chamber premixed mixture in the gasoline-like operation or create suitable conditions for the fuel subsequently injected to burn diffusion in the Diesel-like operation or perform both duties in the mixed gasoline/Diesel-like operation. A single main chamber direct injector is generally needed (for example with H2, CH4 or C3H8 fuels). With NH3, a second main chamber direct injector with H2 is also used to limit the volume of the jet ignition pre-chamber. In this short communications, the results of detailed chemistry simulations with the SRM (Stochastic Reactor Model) suite, a sophisticated engineering tool combining conventional 1D or 3D fluid dynamics approaches are presented to further support these two engine concepts working with fuels H2, CH4, C3H8, NH3, I-C8H18 and N-C7H16 and adopting two different mechanisms for chemical kinetics. Within the limits of the present simulations (a very accurate chemical kinetic for combustion of I-C8H18 and N-C7H16 but a much less accurate chemical kinetic for the other fuels and especially for NH3, unavailability of variable composition and variable properties multiple injections), the Diesel injection ignition and the hydrogen jet ignition are proved to permit combustion modes leading to indicated thermal efficiencies up to 10% better than the latest Diesels at high loads within the same peak pressure and peak temperature constraints.