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Particle image velocimetry measurements of the in-cylinder flow in an optically accessible single-cylinder research engine were taken to better understand the effects of intake pressure variations on the flow field. At a speed of 1500 rpm, the engine was run at six different intake pressure loads from 0.4 to 0.95 bar under motored operation. The average velocity fields show that the tumble center position is located closer to the piston and velocity magnitudes decrease with increasing pressure load. A closer investigation of the intake flow near the valves reveals sharp temporal gradients and differences in maximum and minimum velocity with varying intake pressure load which are attributed to intake pressure oscillations. Despite measures to eliminate acoustic oscillations in the intake system, high-frequency pressure oscillations are shown to be caused by the backflow of air from the exhaust to the intake pipe when the valves open, exciting acoustic modes in the fluid volume.

The thorough understanding of the effects due to the fuel direct injection process in modern gasoline direct injection engines has become a mandatory task to meet the most demanding regulations in terms of pollutant emissions. Within this context, computational fluid dynamics proves to be a powerful tool to investigate how the in-cylinder spray evolution influences the mixture distribution, the soot formation and the wall impingement. In this work, the authors proposed a comprehensive methodology to simulate the air-fuel mixture formation into a gasoline direct injection engine under multiple operating conditions. At first, a suitable set of spray sub-models, implemented into an open-source code, was tested on the Engine Combustion Network Spray G injector operating into a static vessel chamber. Such configuration was chosen as it represents a typical gasoline multi-hole injector, extensively used in modern gasoline direct injection engines.

Combustion properties of hydrogen with N₂ dilution were investigated. The laminar and turbulent burning velocities were examined for outwardly propagating stoichiometric H₂/O₂/N₂ flames varying the amount of diluent N₂. The unstretched laminar burning velocity, ul decreased with the increase in the amount of N₂. Markstein number, Ma, the sensitivity of the flame to the stretch due to the thermo-diffusive effects decreased with the increase in the amount of N₂.

The present study introduces an injection technique for Premixed Charge Compression Ignition (PCCI) combustion in marine diesel engines. It aims to improve the controllability in the spray propagation and obtain the ideal mixture formation through the use of behavior of a merged spray which is formed by a mutual spray impingement between two sprays. Experiment was carried out to confirm the feasibility of controlling the spray propagation in a constant volume chamber. Further, the effects of merged spray propagation on mixture formation, ignition and combustion process have been investigated in a Rapid Compression Machine (RCM).

Gaseous fuel originated from natural gas (NG) has been affected by industrial fields thanks to its low emission feature. The excellent knock resistance of methane, a major component of NG, is another advantage in engine applications, but the composition of NG varies depending on the production region. Methane number (MN) has been widely used to evaluate the knock resistance of certain NG. However, the selection of a reliable knock-resisting index has not been settled because of several definitions of MN, and a new index called the propane knock index was recently proposed. Moreover, the proper index could change with types of gas engines. In this study, a rapid compression-and-expansion machine (RCEM) was prepared to reproduce in-cylinder conditions and combustion processes of a pre-chamber type medium-speed gas engine, and the knocking-like combustion was intentionally generated by setting compression pressure, ignition timing, and fuel density in the mixture to the proper level.

Conventionally, turbulent burning velocity models are compared by showing the model-predicted ST/SL0 ratios in an ST/SL0 - u′/SL0 plane, where ST and SL0 are the turbulent and laminar burning velocities, respectively, with u′ being the turbulence intensity. Such a method applies to only those models which take u′ or u′/SL0 as the only variable of ST or of ST/SL0. In order to analyze and compare most recent models in which turbulence and flame spatial scales (or length scales) are also taken into account because of their importance in combustion, this paper showed the model-predicted ST/SL0 ratios as contours in three planes (Re-Da, ηκ/η0 - u′/SL0 and L/η0 - u′/SL0, where Re, Da, L, ηκ and η0 are the Reynolds number, Damköhler number, turbulence integral scale, Kolmogorov scale and laminar flame preheat zone thickness, respectively); these planes are usually used in discussing the flame structure.

Lean-burn is the most attractive way to lower emissions of NOx while improving the fuel consumption simultaneously in spark ignition engines. A Pulsed Combustion Jet (PCJ) ignition system has a great potential to enhance ignition reliability and burning rate of lean fuel-air mixtures. Its action is based on the utilization of turbulent plumes formed by jets produced by generators, in the shape and size of an ordinary spark plug, that embody a small (500 mm3 or less) cavity, capped with an orifice plate and outfitted with a hollow electrode. Performance characteristics of PCJ were established by combustion tests carried out in a diskshaped, constant volume combustion chamber using lean methane-air mixtures. The results were compared to those obtained with Pulsed Plasma Jet (PPJ) an standard spark plug ignition systems. Lean limit was extended most by PCJ ignition under both quiescent and swirl conditions.

In internal combustion engines, lean-burn is particularly attractive for minimizing pollutant emissions, in particular NOx, with a concomitant improvement in fuel economy. For combustion in lean fuel-air mixtures, achievement of adequate reliability of ignition and sufficiently high burning rate requires special devices. The most effective among them is the injection of active radicals by means of PFJ (Pulsed Flame Jet) ignition system. Presented here is an experimental proof of the action of the hydroxyl (OH) radical produced by such an ignition system. The measuring apparatus used for this purpose was based on PLIF (Planar Laser-Induced Fluorescence), and the effects of equivalence ratio of the mixture in the cavity, cavity volume, and orifice diameter on the variation of OH fluorescence area in the jet and their intensity were revealed quantitatively.

The “Two-Drive-Transmission with Range-Extender” (called DE-REX) is an innovative hybrid powertrain concept using two electric motors and an internal combustion engine. The two electric motors are permanent magnet synchronous motors with a maximum power of 48 kW each. As combustion engine a 3 cylinder, turbocharged engine with a power of 65 kW is used. The aggregates are coupled to a transmission whose layout is characterized by consisting of two parallel 2-speed sub-transmissions. This layout offers a high flexibility and enables both parallel and series hybrid driving. The hybrid control unit (HCU) has to select the optimal driving mode and power distribution between the aggregates in regard to in some extend competing objectives like efficiency, emissions or driving comfort. In particular, the operation of the internal combustion engine with only two gear ratios is challenging.

The scope of this work is to propose a methodology to define multicomponent surrogate mixtures which describe the main evaporation characteristics of real gasoline fuels. Since real fuels are commonly complex mixtures with hundreds or thousands of hydrocarbons, their exact composition is generally not known. Only global characteristics are standardized. An accurate modeling of such complex mixtures in 3D-CFD requires the definition of a suitable surrogate. So far, surrogate mixtures have mostly been defined based on their combustion properties, such as ignition delay or burning velocity, irrespective of their evaporation characteristics. For this reason, in this work, a systematic study is carried out to develop a methodology to define mixtures of representative components that mimic the evaporation behavior of real fuels.

The application of Computational Fluid Dynamics (CFD) for three-dimensional (3D) combustion analysis coupled with detailed chemistry in engine development is hindered by its expensive computational cost. Chemistry computation may occupy as much as 90% of the total computational cost. In the present paper, a new two-step iso-octane combustion model was developed for spark-ignited (SI) engine to maximize computational efficiency while maintaining acceptable accuracy. Starting from the model constants of an existing global combustion model, the new model was developed using an approach based on sensitivity analysis to approximate the results of a reference skeletal mechanism. The present model involves only five species and two reactions and utilizes only one uniform set of model constants. The validation of the new model was performed using shock tube and real SI engine cases.

The discrete multi-component model for residual heavy fuel oil (HFO), developed in the mid-2000s, proved to be a simple but practical approximation in reproduction of the combustion process of HFO sprays on a couple of CFD simulation codes. The model succeeded in providing qualitative explanation about the spray and flame progression of HFO inside constant-volume chambers (CVC), but its practical use is still underway because of its higher calculation costs. Two-component HFO model, which was introduced relatively recently, separates every spray droplet virtually into two smaller droplets of each component to calculate their evaporation process separately. The model showed good agreement with the observation results on the various HFO spray behaviors in some visualized CVCs (VCVCs).

Syngas, is an alternative fuel consisting mainly of hydrogen and carbon monoxide in various proportions. An understanding of the effects of the varying constituents on the combustion characteristics is important for improvement of the thermal efficiency of syngas-fueled engines. The effects of hydrogen concentration and mixture pressure on the turbulent burning velocity of outwardly propagating stoichiometric flames of hydrogen-carbon monoxide-air were studied in a constant volume fan-stirred combustion chamber at a constant mixture temperature of 350 K. The mole fraction of hydrogen in the binary fuel was varied from 0 to 1.0, at mixture pressures of 0.10, 0.25 and 0.50 MPa. The turbulence intensity was kept constant at 3.27 m/s. For fixed mixture pressures, it was found that the turbulent burning velocity increased with an increase in hydrogen fraction primarily due to increase in the unstretched laminar burning velocity.