Main Chamber Pressure Research Articles

Performance metrics for fueled and unfueled turbulent jet igniters in a rapid compression machine

Turbulent jet ignition (TJI) system is an advanced ignition device that uses turbulent jets of hot combusting gases to initiate combustion in the main chamber. TJI system can enable knock mitigation in stoichiometric and lean mixtures, and increase burn rates in ultra-lean mixtures thereby improving efficiency. TJI nozzle design directly affects combustion efficiency since it determines the nature of jet spread in the main chamber. In this study a TJI system using methane as the fuel is used for assessing the performance of single and dual orifice TJI systems in a rapid compression machine (RCM). The prechamber is tested in both active and passive configurations and the volume is fixed at 2% of the main chamber clearance volume. Combustion metrics are derived using the main chamber pressure measurements and high-speed direct imaging of the combustion process. Stoichiometry in the main chamber is varied from λ = 1.0 until the lean limit (λ ~ 3.0). Prechamber fueling begins for mixtures leaner than λ = 1.5 to improve burn rates and extend the lean limit in comparison to the unfueled configuration. Pressure data is used to calculate burn rates and to identify inflection points from the curves of the pressure derivatives. High speed images are used for visualization and to measure flame area and jet penetration. A systematic approach of analyzing TJI nozzle performance is currently lacking and this study aims to address the issue by evaluating the suitability of the metrics used in this work.

Study on the Pre-Chamber Fueling Ratio Effect on the Main Chamber Combustion Using Simultaneous PLIF and OH* Chemiluminescence Imaging

<div class="section abstract"><div class="htmlview paragraph">Pre-chamber combustion (PCC) enables leaner air-fuel ratio operation by improving its ignitability and extending flammability limit, and consequently, offers better thermal efficiency than conventional spark ignition operation. The geometry and fuel concentration of the pre-chamber (PC) is one of the major parameters that affect overall performance. To understand the dynamics of the PCC in practical engine conditions, this study focused on (i) correlation of the events in the main chamber (MC) with the measured in-cylinder pressure traces and, (ii) the effect of fuel concentration on the MC combustion characteristics using laser diagnostics. We performed simultaneous acetone planar laser-induced fluorescence (PLIF) from the side, and OH* chemiluminescence imaging from the bottom in a heavy-duty optical engine. Two different PC Fueling Ratios (PCFR, the ratio of PC fuel to the total fuel), 7%, and 13%, were investigated. The “negative” regions of the PLIF fields were used to visualize PC jets and the MC combustion. The absence of acetone seeding in the PC, and its consumption during the MC combustion contributed to the loss of PLIF signal (negative regions). The instantaneous PLIF/OH* fields showed the appearance of PC jets near its pressure maximum. The PC jet interacting with the piston surface was accompanied by an increase in OH* chemiluminescence intensity and its area. Increasing PCFR resulted in a lag of ~0.6° crank angle in the PC and MC pressure and the pressure difference (Δ<i>P</i><sub>PC-MC</sub>) between the two, for the two PCFR cases. This led to a phase lag in the PC flame jet penetration distance, which in turn delayed the increase in the total OH* chemiluminescence intensity for the higher PCFR case. For similar Δ<i>P</i><sub>PC-MC</sub>, we observed wider OH* regions with increased PCFR. This result distinguished the radical concentration effect on the MC combustion from the fluid mechanical effects controlled by Δ<i>P</i><sub>PC-MC</sub>.</div></div>

Study on the Compensated Flow Control Valve Based on AMESim Code

The working characteristics which included static characteristics and dynamic characteristics were analyzed. On the basis of establishing the characteristic mathematical equations of compensated flow control valve, the feature of static characteristics of the valve was obtained. By mathematical analysis, the relationship of static differential pressures of interior and exterior with original flow pressure P0, main chamber pressure P1 and throttling chamber pressure P2 was ascertained. For main chamber pressure P1, its static value is the linear combination of P0 and P2; for throttling chamber pressure P2, the mathematical expression consists of flow coefficient Cq1 and Cq2, spool throttling diameter d1 and d2, cone half angle of spools α1 and α2, valve opening xpc and xv, velocity coefficient Cv1, leakage matching surface diameter dt and aperture mean width Δdt. The equivalent dynamic simulation model of compensated flow control valve was established by AMESim. Based on the simulation results, dynamic characteristics curves of load, dynamic response of internal and external differential pressure under different parameters were obtained.

Fast mechanical shutter for pulsed ion beam generation

A pneumatically actuated mechanical shutter has been developed for pulsed ion beam operation. The mechanical shutter provides vacuum isolation between the gas filled ion source (nominally at ∼10mTorr) and the high vacuum accelerator chamber (nominally <μTorr), which is essential for applications involving high voltage gradients. In the present design, the FWHM pulse length of the ion beam was measured to be approximately 1.5ms with rise and decay times of ∼1ms. Steady-state pressure measurements show an order of magnitude decrease in the main chamber pressure by incorporating the shutter.

Neutrals Studies on Alcator C-Mod

The high neutral densities and short neutral mean-free-paths in the Alcator C-Mod divertor have provided a unique testing ground for our understanding of the role of neutrals in a tokamak. The high neutral pressures found in the C-Mod divertor can be reproduced in models only by including such processes as ion-neutral and neutral-neutral collisions and neutral viscosity, as well as taking into account the plasma in the private flux region. After detachment, when the divertor plate ion flux has dropped by more than an order of magnitude, the divertor pressure still remains high. High neutral collisionality and the plasma in the private flux region again help keep neutrals in the divertor along with the large source of neutrals due to recombination. Likewise, diffusive neutrals are the explanation for the divertor neutral pressure’s insensitivity to strike point position. Closure of neutral leakage pathways did not lead to a decrease in neutral pressures in the region outside the divertor - the main chamber. This observation prompted further research, which showed that ion fluxes to main chamber surfaces rival those reaching the divertor plates; the main chamber pressure can be primarily determined by the level of ion transport perpendicular to the magnetic field. This finding has spawned a host of studies (active and passive) both at C-Mod and other tokamaks to understand how radial transport can be so large.

Divertor bypass in the Alcator C-Mod tokamak

The Alcator C-Mod divertor bypass has for the first time allowed in situ variations to the mechanical baffle design in a tokamak. The design utilizes small coils which interact with the ambient magnetic field inside the vessel to provide the torque required to control small flaps of a Venetian blind geometry. Plasma physics experiments with the bypass have revealed the importance of the divertor baffling to maintain high divertor gas pressures. These experiments have also indicated that the divertor baffling has only a limited effect on the main chamber pressure in C-Mod.

Experimental and simulation analysis of the transient operation of a turbocharged multi-cylinder IDI diesel engine

SUMMARY An experimental and theoretical analysis is carried out to study the response of a multi-cylinder, turbocharged, IDI (indirect injection) compression ignition engine, under transient operating conditions. To this aim, a comprehensive digital computer model is developed which solves the governing di⁄erential equations individually for each cylinder, providing thus increased accuracy over previous ‘single-cylinder’ simulations. Special attention has been paid for diversifying the transient operation from the steady-state one, providing improved or even new relations concerning combustion, heat transfer to the cylinder walls, friction, turbocharger and aftercooler operation, and dynamic analysis for the transient case. An extended steady state and transient experimental work is conducted on a specially developed engine test bed configuration, located at the authors’ laboratory, which is connected to a high-speed data acquisition and processing system. The steady-state measurements are used for the calibration of the individual submodel constants. The transient investigation includes both speed and load changes operating schedules. During each transient test four major measurements are continuously made, i.e. engine speed, fuel pump rack position, main chamber pressure and turbocharger compressor boost pressure. The hydraulic brake coupled to the engine possesses a high mass moment of inertia and long nonlinear load-change times, which together with the indirect injection nature of the engine are important challenges for the simulation code. Explicit multiple diagrams are given to describe the engine and turbocharger transient behaviour including smoke predictions. The agreement between experimental and predicted responses is satisfactory, for all the cases examined, proving the validity of the simulation process, while providing useful information for the engine response under various transient operations. ( 1998 John Wiley & Sons, Ltd.

A131 非定常火炎噴流による定容燃焼容器内予混合ガスの着火・燃焼過程の可視化観察

Ignition and combustion processes in a prechamber combustor by a flame jet are experimentally investigated using schlieren photography. The effects of the nozzle diameter on the structure of flame jet, ignition process, and subsequent combustion process in the main chamber are examined by combining schlieren observations and main chamber pressure histories. The structure of flame jet is found to be greatly influenced by the nozzle diameter, and can be classified into four types; a high speed jet of hot combustion products without flame kernels, one including a small amount of flame kernels and rich active species, a relatively high speed jet containing with flame kernels, and a low speed flame column. Depending on these flame jet properties, the ignition and combustion processes in the main chamber are also divided into four types; extinction of a flame jet, extremely rapid explosion after a long ignition delay time, relatively rapid turbulent combustion with fine wrinkles, and spherically propagating slow wrinkled laminar combustion.

Ignition and burning process in a divided chamber bomb

Ignition and burning mechanisms of the main chamber mixture by a torch jet were experimentally investigated using a divided chamber bomb. The effects of the nozzle diameter and volume ratio on the structure of the torch jet, ignition process, and subsequent burning process in the main chamber were minutely examined, in both uniform and stratified charges, by measurements of ion current, light emission, OH-emission (306.4 nm), initial torch jet velocity, and main chamber pressure histories and by schlieren photography. The structure of the torch jet was greatly influenced by the nozzle diameter and volume ratio independently of the main chamber mixture ratio. According to the physical and chemical characteristics obtained for it, the structure of the torch jet could be classified into four types, and the ignition and burning processes in the main chamber could also be classified into four patterns depending on the torch jet structure: pattern I, chemical chain ignition and well-dispersed burning; pattern II, composite ignition and well-dispersed burning followed by wrinkled laminar burning; pattern III, flame kernel torch ignition and wrinkled laminar burning; and pattern IV, flame front torch ignition and wrinkled laminar burning. Combustion characteristics such as main chamber pressure and net burning time in the main chamber also showed their own peculiar features. Examination of the lean flammability limit gave a possibility of lean burning outside of the normal flammability limit by using divided chamber systems. From these results combustion pattern II was found to be most favorable for lean burning.