Ignition Mode Research Articles

Comparative analysis of waste tire pyrolysis oil and gasoline as low reactivity fuel in RCCI engine

ABSTRACT The utilization of alternative fuels in internal combustion engines has gained significant attention due to concerns about energy security and environmental sustainability. Waste tire pyrolysis oil (WTPO) is a potential alternative fuel that can be produced from waste vehicle tires through a pyrolysis process. In this study, the possible use of WTPO in a diesel engine operating under Reactivity Controlled Compression Ignition (RCCI) mode was investigated. In the study, the use of WTPO as a low-reactivity fuel in RCCI engines is examined, highlighting the importance of innovative approaches to alternative fuels with varying reactivity levels for effective combustion control and emission reduction. In the experimental work, WTPO was tested at different energy rates of 15%, 30%, and 45% into the intake port using the PFI system, while conventional diesel fuel was injected directly into the cylinder by the CRDI system. The tests were carried out under different engine load conditions while maintaining a constant engine speed of 2400 rpm. The performance, combustion, and emission characteristics of the engine were analyzed and compared between WTPO and conventional gasoline fuel as LRF. The study results show that using WTPO in RCCI operation with sustainable ringing intensity leads to significant increases in Brake Thermal Efficiency (BTE) compared to gasoline usage, with BTE increments of up to 5%, 3.3%, and 6.3% observed with increasing engine load. Furthermore, WTPO usage in RCCI engines effectively reduced hydrocarbon (HC) emissions, addressing a significant issue, and maintaining the known benefits of reactivity-controlled combustion. These findings suggest that WTPO can be utilized as a viable low-reactivity fuel in RCCI engines with acceptable performance, combustion, and emission characteristics.

An optical investigation on the effects of split-injection on hydrogenated catalytic biodiesel/gasoline dual-fuel engine under cold start conditions

Reactivity-controlled compression ignition (RCCI) mode has emerged as a promising technology for internal combustion engines, offering precise combustion phase control and the potential to meet stringent emission regulations. However, RCCI mode faces challenges, particularly misfiring during cold start conditions. This study proposes a solution by utilizing hydrogenated catalytic biodiesel (HCB) as a pilot fuel for gasoline and implementing a split-injection strategy to address the challenge. Experimental research was conducted on an optical engine under cold start conditions, incorporating three split-injection strategies: P30M70 (30 % main-injection and 70 % pilot-injection), P50M50, and P70M30. The results demonstrate that although gasoline can only be ignited by the main-injected HCB under coldstart conditions, the in-cylinder environment becomes more dynamic due to the pilot-injection. Consequently, split-injection reduces ignition delay by up to 7.09 °CA and shortens the combustion stage compared to single-injection. Among the various injection strategies examined, P30M70 demonstrated outstanding in-cylinder heat release performance, surpassing other split-injection strategies by up to 26.77 J/CAD, and outperforming the single-injection by 22.94 J/CAD. Visualization tests indicate that applying the P30M70 strategy leads to higher soot production under conditions of delayed main-injection timing (-15 °CA ATDC). However, the peak flame area under cold-start conditions is 53.16 % greater than P50M50 and 71.28 % greater than P70M30, highlighting excellent flame propagation characteristics. The average in-cylinder temperature suggests that a larger visible flame area contributes to engine warming. Despite the inherent trade-off, the dual-fuel mode of HCB/gasoline proves suitable for RCCI engines, with the P30M70 split-injection strategy being recommended for the cold start stage.

Improvement of technology and technique for the production of sinter at the SP EVRAZ KGOK. Report 1. Loading and ignition of the mix.

A brief literature review of theoretical and applied works on charging and ignition of sinter mix has been made. The review considers experimental data on the influence of the distribution of the particle size of the mix and the fuel content over the height and width of the bed, and its bulk density on the consumption of solid fuel, height and gas permeability, on the productivity of sinter machines and sinter strength. The problems of sinter mix ignition, the influ-ence of throttling of the first vacuum chambers of sinter machines on the quality of sinter and gas consumption for ignition are discussed. The results of industrial studies of mix loading and ignition modes on EVRAZ KGOK sinter ma-chines are presented, which provide an increase in the bed height, an increase in the cold strength of the sinter, and a decrease in natural gas consumption for mix ignition. As a result of increasing the rotational speed of the drum feeder, the discrete descent of the mix from the mix flow stabilizer was eliminated. It has been established that due to the ex-pansion of the sinter pallets and the negative slope of their sides, there is no need to form a mix bed profile variable in height and width. The operation of sinter machines with and without separation of the loading chute from the bed has been studied. The presence of critical fluctuations of the grain size composition of the mix and the content of fuel car-bon in it along the width and height of the bed for both options of operation, due to the mode of operation of the shuttle mix distributor and fluctuations the height of the bed in the intermediate hopper, has been established. The important role of the design and mass of the mix smoother has been experimentally confirmed. The design of the throttling device of the vacuum chambers legs with manual change of the free section only as it wears out has been developed and implemented. The rational free section of the legs of the vacuum chambers is determined, which provides a minimum suction (1–2 Pa) in the chamber of the ignition hearth, and equal to 10–12%. As a result of the introduction of new technical solutions, an increase in the cold strength of the sinter by 1.09%, a decrease in natural gas consumption by 29%, and an increase in the height of the sintered charge layer up to 30 mm were achieved without reducing the productivity of sinter machines

On the flow-facilitated ignition in a mixture with low Lewis number

The imposed laminar flow has been shown to facilitate ignition under certain conditions in our previous work (Chen et al. 2023). Such flow-facilitated ignition (FFI) was observed only for mixtures with sufficiently large effective Lewis numbers, i.e., Le>>1. It is not clear whether FFI can also occur in a mixture with Le<1 and Le∼1. This study will investigate the occurrence of FFI in a mixture with low Lewis number. We conduct multi-dimensional simulations of forced ignition by a pair of electrodes in both static and flowing hydrogen/air mixtures. A simplified ignition model is used in simulations. The laminar flow direction is perpendicular to the pair of electrodes. We consider different values for equivalence ratio (ϕ=0.4 and 1.0), pressure (P = 0.3–1 atm), electrode gap distance (dgap=0.64–3.88 mm) and flow velocity (Uin=0–10 m/s). The simulation results show that FFI can occur in a fuel-lean (ϕ=0.4) H2/air mixture with Le≈0.43 at sub-atmospheric pressure. This indicates that large Lewis number is not a necessary condition for FFI occurring in simulations considering a simplified ignition model. Here, the favorable conditions for FFI are large critical ignition radius at sub-atmospheric pressure, sufficiently small electrode gap distance and moderate flow velocity. Moreover, the reduction in heat loss to the electrodes by the imposed flow is found to be crucial for FFI. To further understand the boundary conditions of FFI, an ignition mode regime diagram in terms of flow velocity and normalized critical ignition radius (i.e. the ratio of critical ignition radius and electrode gap distance) is proposed. The present study provides insights on the effects of laminar flow on forced ignition of premixed flames.

Multi-objective optimization of a compression ignition engine using on-board methanol reforming

The dual-fuel combustion technology utilizing hydrogen and diesel fuel shows potential in enhancing the performance of compression ignition engines and reducing carbon emissions. However, this approach is accompanied by several significant challenges, such as hydrogen transportation and storage, as well as low combustion efficiency at low loads. To address these challenges, this study integrates low-temperature combustion technology with online hydrogen production through methanol steam reforming to achieve efficient and clean combustion. The results of methanol steam reforming, mainly consisting of hydrogen, carbon dioxide, and unreacted methanol, is premixed via port injection as a low-reactivity fuel. Simultaneously, diesel fuel is directly injected into the cylinder as a high-reactivity fuel to achieve reactivity-controlled compression ignition mode. The primary fuels employed in compression ignition engines comprise reformate gas (mainly hydrogen), unreacted methanol, and diesel. This combination is collectively termed as tri-fuel combustion. This study utilizes a combination of genetic algorithms and 3D engine simulation to determine the optimal strategy for the methanol/reformed gas/diesel tri-fuel engine under different loads. The results of the optimization reveal that the tri-fuel combustion mode has the highest indicated thermal efficiency, surpassing the methanol/diesel dual-fuel mode and the reformed gas/diesel dual-fuel mode. Meanwhile, the optimized engine demonstrates significantly lower NOx and soot emissions than those required by the Euro VI emission regulations. Additionally, the study summarizes engine operating parameters impact on performance. Moreover, the tri-fuel combustion mode has a distinct advantage in increasing the methanol energy substitution rate at all three different loads. The dual-fuel mode leads to increased unburned hydrogen and methanol concentration near cylinder liner due to lower combustion temperature. In contrast, tri-fuel mode substantially reduces unburned hydrogen and methanol due to high combustion temperature and methanol reactivity.

Effect of Diesel Injection Strategy and Ammonia Energy Fraction on Ammonia-Diesel Premixed-Charge Compression Ignition Combustion and Emissions

The utilization of ammonia as a fuel is one of the effective measures to achieve decarbonization and carbon neutrality in internal combustion engines (ICEs). However, its slow laminar flame speed and high ignition energy limit the efficient application of ammonia-only in ICEs. In this study, based on a heavy-duty single-cylinder engine, the impact of ammonia energy fraction (AEF), start of diesel injection (SODI) timing, and diesel injection pressure (DIP) on combustion and emission characteristics of premixed-charge compression ignition mode under low load conditions was investigated. Combined with three-dimensional simulation, the mechanism of how AEF and diesel injection strategy regulation affected the in-cylinder equivalence ratio and reactivity distribution was analyzed. It was found that increasing the AEF and advancing the SODI timing can improve the homogeneity of mixture. However, the spatial distribution of the OH groups deteriorate continuously. Experimental results indicated that with the used of 50% AEF, 60 MPa DIP, and injecting diesel at −40°CA ATDC, a gross indicated thermal efficiency (ITEg) of 49.7% can be achieved. Compared to the diesel-only mode, the greenhouse gas (GHG) emissions reduced by 44%. To further improve the combustion of ammonia/diesel PCCI mode, the DIP was increased to 100 MPa, which optimized the in-cylinder fuel–air mixing process, improving the homogeneity of the mixture and enhancing the reactivity distribution before the ignition, and enabling faster combustion. As a result, an increase in ITEg to 51.4% with using 100 MPa DIP was achieved, and reduced the GHG emissions by 51% compared to the diesel-only mode.

Experimental observation of the TJI-initiated HPDI gas combustion: Vertically crossed flame jet and methane jet

In the field of natural gas marine engines, the high-pressure direct injection (HPDI) technology is widely used to achieve emission reduction while maintaining equivalent thermal efficiency and power output compared to diesel engines. In these engines, the in-cylinder combustion is primarily initiated by the diesel spray flame near the top dead center (TDC). In the present work, pre-chamber turbulent jet ignition (TJI) is employed to substitute diesel injection to initiate the combustion of HPDI methane jets. The optical experiments of ignition and flame development in the TJI-HPDI system with various injector configurations and injection/ignition control parameters are conducted in a constant-volume combustion chamber (CVCC). It is revealed that with the increase of injection-ignition delay(ti), three ignition modes are observed sequentially: methane jet suppresses ignition, methane jet first suppresses ignition then promotes flame propagation, and direct ignition and promoted flame propagation. The effect of various injection-ignition delays and injection pulse width were explored. The injection-ignition delay significantly influences the combustion characteristics such as heat release rate, while the injection pulse width influences the duration of the lifted jet flame. The flame lift-off length first decreases and then increases due to variations in thermodynamic conditions and oxygen concentration. With a larger-nozzle injector, the critical injection-ignition delay to initiate the main chamber combustion is significantly reduced. Moreover, the use of different nozzle diameters leads to varying levels of turbulent intensity in the methane jet, which in turn affects the combustion behavior.

Experimental study on fire spread behavior of single 110 kV cable under different layout conditions

High-voltage cable fire accidents can cause large-scale power outages. In particular, the 110 kV large-section (diameter 10 cm) cable has complex cable structures. Therefore, based on the actual cable laying scenarios, three cable layout conditions are set, including the horizontal cable above horizontal floor structure (HCAHFS), the inclined cable above horizontal floor structure (ICAHFS), and the inclined cable above inclined floor structure (ICAIFS). The combustion behaviors and flame spread characteristics of 110 kV large-section cable are experimentally studied. It is found that the flame cannot spread on the surface of the flame-retardant outer sheath of the cable. However, when the cable-floor distance (lcf) is between 0.75 d and 2 d (d is the cable diameter) in HCAHFS, i.e. there is a floor under the cable that can catch cable melt, and the flame spread characteristics is different. After the cable is ignited, the cable fire can be divided into two parts, outer sheath flame and melt flame, and the cable fire can spread under the joint action of two flames. When lcf ≤ 0.75 d, the space under the cable is narrow. With the accumulation of melt on the floor, air entrainment is limited during cable combustion, resulting in the cable flame unsustainable. When lcf ≥ 2 d, the thermal radiation and convection from the melt and outer sheath flame to the cable preheat zone are weakened, resulting in cable flame extinction as well. In ICAHFS, the cable flame spread rate is first increased and then decreased with the increasing lcf at the fixed inclination angle; In ICAIFS, the upward spread rate of cable flame is faster than the downward spread rate at the fixed inclined angle. Moreover, the cable flame spread rate (FSR) in HCAHFS is the slowest compared to that in ICAIFS with different inclined angles. The preheating length for ICAIFS increases under both upper and lower ignition modes, while it is obviously at upper ignition, due to the melt flow. Finally, a correlation of FSR was proposed for various ignition positions and inclined angles. This study provides a reference for fire protection design and numerical simulation parameter setting of 110 kV cable fire.

Transition from Fast-Flame to Detonation

Flame acceleration within a channel is facilitated by repeating obstacles that generate turbulence. As the flame accelerates to supersonic velocities, it generates compression waves that coalesce to form a strong leading shock. This shock-flame complex continues to accelerate until it reaches a maximum velocity equal to the speed of sound in the combustion products; the complex is referred to as a fast-flame. Shock reflection driven onset of detonation may occur, characterized by an instantaneous jump in velocity to the theoretical ‘Chapman-Jouguet’ velocity. A more fundamental problem is the transition from a fast-flame to detonation without the presence of obstacles. &#x0D; In the current study, a 7.6 cm square ‘optical section’ housing a perforated plate was used to study the transition from fast-flame to detonation. A spark- and glow- plug served as ignition sources. The optical section had windows installed on its side and end walls so that Schlieren- and direct- photography could be captured. Soot foils were also utilized to record detonation cell structure. The fast-flame was generated by the passage of a detonation wave through the perforated plate, after which the transition to detonation could be studied. &#x0D; Gaseous fuel-oxygen mixtures of varying degrees of detonation stability over a wide range of pressures were tested. In low-pressure tests, delayed onset of detonation was observed, and detonation initiation sites were located at the channel walls indicating that flame-generated turbulence alone is not sufficient for the transition process. As pressure was increased, onset occurred immediately after the perforated plate at various locations across the channel cross-section, not strictly at the walls. For this abrupt ignition mode, transverse shock collisions played an important role in the transition to detonation. &#x0D;

Identifying two ignition modes of polymer insulated wires with continuous excess current in microgravity

Overload ignition of electric wires in microgravity has been investigated for space fire safety. Microgravity experiments from drop towers and parabolic flight have been conducted to observe the overall ignition phenomena. Two-dimensional numerical simulations were performed employing finite-rate chemistries in both condensed and gas phases. As the applied current changes, two distinct ignition modes were found in both experiments and simulations, one away from the wire and the other near the wire surface, named “spontaneous ignition” and “wire assisted ignition”, respectively. After validating ignition delay times by experiments, the simulation results were used to discuss the transition of two ignition modes. With a lower current, the spontaneous exothermic reaction at the pyrolysis gas front led to the far-distance ignition. While with a higher current, the local heat loss suppressed spontaneous ignition; meanwhile, the excessive heat from the exposed core wire caused the surface ignition. In addition, the ignition energy showed a non-monotonical increase with the applied current, where the minimum ignition energy was consumed with 5.5 A current supply implying the high fire risk of the “spontaneous ignition” regime. The control mechanisms of the ignition energy change in different stages were discussed.

Effects of temperature and composition inhomogeneity on the ignition characteristics of NH3/H2 co-firing fuels under HCCI operating conditions

The application of ammonia (NH3) in combustion devices, such as internal combustion engines (ICEs), is expected to largely reduce the greenhouse gas (CO2) emission. NH3/H2 cofiring fuels in homogeneous charge compression ignition (HCCI) engines may provide a potential way to deal with zero carbon requirements. However, in HCCI engines, the ignition process needs to be moderated since the ignition is only controlled by the chemical kinetics of the fuel. Therefore, this study investigates the effects of temperature and composition stratification strategies on the auto-ignition characteristics of NH3/H2/air mixtures under HCCI engine operating conditions with direct numerical simulation (DNS). 12 cases with different stratification strategies have been set under turbulent conditions. The chemical kinetics of NH3/H2/air was verified with the laminar flame speeds and ignition delay times. Results show that the temperature stratification can reduce the peak value of heat release rate (HRR), advance the ignition time and extend the combustion duration. In this case, the chemical reaction front is dominated by the deflagration or flame propagation mode. However, in contrast, composition stratification shows very limited effect on the overall combustion process, which is similar to homogeneous ignition and denoted as the spontaneous ignition mode. When increasing the hydrogen content in the fuel, the ignition time is obviously advanced and the peak of HRR is slightly increased. Higher NO emission is also observed which is mainly due to the increase of O, H, and OH intermediates to enhance the fuel NO production. Temperature stratification degree can improve the ignition process under both negatively correlated or unrelated T-Φ fields. However, the improvement is more evident for unrelated T-Φ condition when increasing the stratification degree.

Assessing the effect of air-throttling on ignition dynamics in a hydrogen-fueled scramjet under various fuel-injection strategies using LES

Air-throttling has been experimentally substantiated as a potent technique for augmenting the ignition of fuel jets in high-speed scramjet engines. Nonetheless, the elucidation of its combustion enhancement mechanism remains conspicuously scant in the extant literature. In this work, a comprehensive numerical investigation was conducted to assess the ignition dynamics of a hydrogen-fueled cavity-stabilized scramjet combustor under various fuel-injection and air-throttling strategies using large-eddy simulation. The results demonstrated that air-throttling could improve the ignition environment by augmenting backpressure, fuel residence time, and mixture homogeneity. Remarkably, the subsonic region was improved by over 30%, and the maximum Mach number was limited to no more than 2.25. Additionally, the enhanced ignition modes under two injection strategies were quite different. For the passive injection, the flame developed rapidly as a result of the deflagration of lean mixture in the interval of Zmix = [0.01, 0.02]. Nevertheless, the direct injection resulted in an additional deflagration-to-detonation transition phenomenon in the expansion section due to the ignition of rich mixture in the interval of Zmix = [0.0225, 0.03]. Both injection strategies exhibited severe flow separation and flame flashback. After removing air-throttling, the flame became dispersed with large-amplitude fluctuations, emphasizing the importance of precise control of air-throttling parameters and operating sequence. These findings advanced the current understanding of the intricate interactions between pilot-hydrogen and air-throttling, thereby elucidating their pivotal role in promoting ignition within high-speed environments.

Investigation of the effects of flame surface development on the ignition mechanism of aero-engine combustors

Large eddy simulation was employed to simulate the effects of different vane angles of the primary and pilot stages on the ignition process of a combustor under normal temperature and pressure conditions. The simulation results of different vane angles of the pilot stage were then verified experimentally. Kernel initiation and flame propagation in the cases of ignition success and failure were analysed. It was found that in the ignition failure case, the flame kernels are confined to the downstream zones of the venturi and cannot propagate radially, and almost no negative displacement exists in the axial direction. However, in the ignition success case, sub-fire kernels are always present outside the radial boundary of the primary stage. Five ignition modes were finally proposed: (I1) typical ignition, (I2) relatively high-speed ignition, (I3) single-kernel alternating dominant, (I4) main kernel dominant, and (I5) dual-kernel dominant modes. Using high-speed photography, the flame shape changes and ignition characteristics in the cases of successful and failed ignition with different pilot-stage vane angles were investigated.

High-Resolution Two-Dimensional Numerical Simulation of n-Heptane/Air Autoignition Under the Influence of Temperature Fluctuation

ABSTRACT High-resolution two-dimensional numerical simulations are performed to investigate n-heptane/air autoignition process under different initial temperatures with varied levels of temperature fluctuations. It is found that temperature fluctuation has an important impact on the autoignition process, and its effects depend on the initial mean temperature. When is located at the upper turning point of the negative temperature coefficient (NTC) regime, as the temperature fluctuation increases, the autoignition mode evolves from a single-stage ignition mode controlled by high-temperature chemistry (HTC) to a mode characterized by the coexisting of multi-stage and single-stage ignition. Both the first-stage heat release and ignition delay increase, but the overall heat release and the total ignition delay decrease. In the presence of a large temperature fluctuation, the low-temperature chemistry (LTC), and HTC reactions, single-stage and two-stage ignitions could coexist in the domain. Chemical explosive mode and sensitivity analyses are performed to identify the reaction mode and the key element reactions in the mutli-stage autoignition process. The temperature fluctuation has a significant promotion effect on the overall ignition except when is located at the lower turning point of the NTC regime. Overall, the NTC phenomenon is weakened under the influence of temperature fluctuation, approaching to zero temperature coefficient (ZTC) phenomenon.

High-efficiency combustion of gasoline compression ignition (GCI) mode with medium-pressure injection of low-octane gasoline under wide engine load conditions

Gasoline Compression Ignition (GCI) mode with medium injection pressure has the potential to achieve high engine efficiency while keeping costs low. In this study, the combustion and emission characteristics of GCI mode with medium-pressure injection of low-octane gasoline were studied and compared to conventional diesel combustion (CDC) under wide engine loads. The results showed that under low to medium loads, GCI mode had improved particulate emissions and indicated thermal efficiency (ITE) compared to CDC mode. However, at high loads, the PM emissions were much higher than CDC mode, and the ITE decreased for IMEP increasing from 10 to 12 bar due to limited injection pressure. To address this, a dual direct injection GCI mode with medium injection pressure was proposed to improve combustion under high loads. With this strategy, NOx emissions were significantly reduced, and ITE was simultaneously improved for IMEP of 10 and 12 bar. Using low octane gasoline and dual direct injection, the ITE of GCI mode can reach or exceed 50% for IMEP from 4 to 12 bar. Compared to gasoline with a research octane number (RON) of 83, gasoline with an RON of approximately 72 had higher ITE under most tested conditions and is recommended as the fuel for GCI mode.

Nanosecond repetitively pulsed discharges and conventional sparks of ammonia-air mixtures in a fan-stirred cruciform burner: Flammability limits and ignition transition

Ammonia, an efficient hydrogen carrier, is crucial for achieving net-zero emissions. However, its low reactivity, as manifested through small unstretched laminar flame speed (SL,0 ∼ 7 cm/s) and large laminar flame thickness (δL ∼ 2.85 mm) at atmospheric pressure and stoichiometric conditions together with narrow flammability limits, makes it difficult for initiation. As such, how to measure accurately ammonia minimum ignition energies under laminar and turbulent conditions (MIEL and MIET) and identify ammonia flammability limits are important to understand fundamental challenges and restricted usage for practical applications. We apply both nanosecond-repetitively-pulsed-discharges (NRPD) and conventional sparks (CS) via the same stainless-steel electrodes of 1-mm diameter with sharp ends at a fixed gap of 2 mm in the same fan-stirred cruciform burner to identify flammability limits of ammonia/air mixtures for spherical flame initiation. The burner is capable of generating near-isotropic turbulence having roughly equal magnitudes of r.m.s. turbulent fluctuating velocities in all three directions (u′) with negligible mean velocities. We find that NRPD operated at a pulse repetition frequency of 40 kHz can promote ignition or decrease the MIE on fuel lean and fuel rich sides as compared to that of CS. However, even using 2,000 pulses with a total ignition energy of 4.4 J for NRPD, no self-sustained flame propagation can be observed at ϕ = 0.65 and/or ϕ = 1.44 that marks lean and/or rich flammability limits for spherical flame initiation. Moreover, we also find a turbulent ignition transition for the stoichiometric ammonia/air mixture, of which the increasing slopes of MIET/MIEL versus u′/SL change drastically from gradually to exponentially at a critical value of (u′/SL)c ≈ 13 for both NRPD and CS. Finally, these results should be useful for future practical applications of premixed ammonia/air combustion.

Novel approach for efficient operation and reduced harmful emissions on a dual-fuel research engine propelled with hydrogen-enriched natural gas and diesel

ABSTRACT The stricter emission norms have created a need to study recent combustion technology in internal combustion engines. Dual-fuel (DF) combustion technology is one of the key techniques to achieve future emission goals. Natural gas is one of the easily available low-reactive fuels worldwide that can be used in the DF combustion strategy. The main problem with using NG in the DF strategy is its lean-burning ability to produce emissions like HC and CO. The combustion losses associated due to crevice losses in the piston geometry are also the reasons for getting degraded engine performance. In the present study, the lean flammability of NG was improved by enriching it with hydrogen. The combustion losses were reduced using modified disc piston geometry with lower crevice volume. The results showed that the thermal efficiency obtained using HENG/diesel DF strategy with disc piston (DF disc) was only less than 0.3%, 0.4%, and 1% for low, mid, and high load conditions compared to conventional compression ignition mode using bowl piston (CI bowl). The change in piston geometry from bowl to disc type using the DF strategy improved the thermal efficiency by about 3.8%, 3.3%, and 2.7% for three load conditions. The NOx and smoke opacity reduction by about 6% to 19% and 40% to 60% in DF disc mode was achieved compared to CI bowl mode.

Key Modes of Ignition and Maintenance of Corona Discharge in Air

Theoretical and experimental studies of various modes of corona discharge operation in atmospheric pressure air are presented in this short review. The original results of modeling negative corona discharges are presented, taking into account the non-stationary plasma-chemical kinetics of charged particles in air plasma. The space–time evolution of the discharge in needle-to-plane geometry is investigated and analyzed. Several stages of discharge development are revealed from the moment of initiation of a low-negative current corona to the quasi-stationary mode of a glow discharge. Experimental data of the authors are presented. Modern technology and diagnostic equipment with a wide variation of the main parameters (the shape and polarity of the applied voltage, the type of gap, etc.) was used. The measurement of the optical characteristics of the plasma glow was carried out with high spatial resolution. Corona discharge current pulse profiles in the air at atmospheric pressure have been recorded with subnanosecond time resolution. With a positive polarity of the pin electrode and high voltage, a transition from a spherical streamer initiating a corona discharge to a cylindrical streamer is shown. The author’s results are rigorously evaluated through a critical comparison with findings from other research groups.

Study on chemical kinetics and NO behaviors in pre-chamber jet-induced ignition mode with ammonia

Ammonia has been supposed to be an important carbon-neutral fuel for the applications in future engines. Its unique physical and chemical properties have great effect on engine combustion. The pre-chamber jet-induced ignition mode can yield very high turbulent jet ignition energy, which should be favorable for the ammonia combustion. To study the effects of key initial parameters in this combustion mode, the ammonia combustion and NOx formation processes were analyzed deeply in constant volume combustion chamber. A 3D CFD model was developed and validated with the visualization experiments, and the initial pressures (Pin) and temperatures (Tin) were numerically studied. The comparisons of different Pin for constant fuel mass (CFM) and constant equivalence ratio (CER) showed that Pin with CFM affects the combustion phase and burning rate more obviously. A higher Pin reduces the NOx emission slightly for CER but leads to higher NOx obviously for CFM, and a higher Pin for CFM also results in a slightly higher N2O emission due to the lower combustion temperature. The comparisons of different Tin showed that a higher Tin can enhance the combustion process greatly, while it also results in higher NOx due to high activity of OH and HNO for HNO + OH → NO+H2O.

Experimental observation of the combustion modes based on a novel multistage pre-chamber turbulent jet ignition (TJI) system

Transient jet flame propagation under newly proposed multistage pre-chambers is studied in a constant-volume combustion chamber with a high-speed schlieren photography system. Various combustion behaviors, including the flame tip velocity, jet emergence timing, projected flame area, pressure, and heat release rate, are investigated under different pre-chamber structures. The present work will provide constructive insight into the design, manufacture, and application of turbulent jet ignition engines. It is shown that the pre-chamber structure determines the main chamber flame development by influencing the flame development inside the pre-chamber. As the flame is accelerated by an obstacle in the pre-chamber, faster exit velocity of hot jet and intense turbulence are observed in the main chamber. In addition, the overall development of the jet flame in the main chamber can be separated into two stages, the former of which is dominated by jet flows, while the latter stage is controlled by the chemical reaction under different excess air coefficients, presenting turbulent combustion characteristics. In this work, six ignition modes under ultra-lean conditions are observed, including (1) jet ignition occurrence on the entire jet surface due to the sufficiently high reactivity; (2) local ignition in the middle of the hot jet; (3) local multipoint ignition and ignition at the jet tip; (4) ignition induced by delayed burning at the jet root; (5) jet tip ignition with backward flame propagation; and (6) global extinction. For the effect of initial pressure, it is found that under stoichiometric conditions, the initial pressure has a minor influence on flame tip propagation, while it significantly influences pressure evolution and heat release rate. However, the increase in initial pressure can improve flame propagation and pressure evolution under lean conditions. Under near-extinction conditions, the ignition mode could be switched from unstable ignition to stable ignition. A numerical simulation is also conducted to reveal the flame development inside the pre-chamber under different pre-chamber structures.