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Exhaust gases of diesel engines may be cleaned of particulates fairly effectively by filtering the gases through various types of beds. Filter regeneration is however, necessary to maintain a clean filter and to keep its flow resistance low. Uninterrupted regeneration may be achieved by burning up the trapped particulates in a continuous manner. Under high engine load conditions, this is attainable by reducing the ignition temperature of the particulates by means of suitable fuel additives, or by means of an appropriate catalytic coating of the relevant filter components. However, under low engine loads, the exhaust gas temperature might be too low and another sensible method has to be employed to continuously ignite the particulates. Apparently, the minimum required exhaust temperature may be achieved over a fairly wide range of engine operation conditions by using several simple-to-employ means.

Reliable initiation of flame kernel development by an electrical spark in IC engines operating at ultra-lean air-fuel mixtures lays down specific demands to spark discharge variables. The demands become especially strict under conditions of intensive mixture motion through the spark gap. The main goal of this study was to determine experimentally the minimum values of spark duration and spark current in the glow phase of the discharge necessary for reliable ignition of methane-air mixtures with equivalence ratios of 0.7 down to 0.6. Different combinations of flow velocity and spark plug orientation with respect to mean flow vector have been considered. A special experimental ignition system was employed to set up spark discharge variables. Besides, a numerical study of early flame kernel development under conditions used in the tests has been carried out.

Flash boiling occurs when a liquid which initially is in a subcooled state, rapidly depressurized to a pressure sufficiently below saturation pressure to initiate a rapid boiling process. This phenomenon can be applied to improve fuel atomization in spark-ignition engines. In the present work, the characteristics of the generated spray were investigated experimentally. This is in order to establishing a designer guideline, for this high potential type of fuel injectors. The following conclusions have been derived: 1. A typical droplets Sauter mean diameter in the range of 20-40μm can easily be achieved with the present simple fuel injection system. 2. The SMD decreases with the increasing in the mole fraction of the propellant; at high pressure however (high propellant content), the SMD is less and less affected. 3. The SMD and the droplets' uniformity are independent of the orifices' size. 4. The SMD increases with the axial distance. 5.

The relationship between the characteristics of a spray pattern that is generated by a simple external-mixing plain-jet atomizer, in pulse mode, and the control parameters of the injection system, has been investigated experimentally. The experimental conditions varied in the range of Re=1236 to 3540, We=65 to 595, and air/liquid velocity ratio from 15 to 110. The pulse duration varied between 3.4 and 18.5ms. It was found that, 1. the Sauter mean diameter is proportional to (Vf/Va3)0.5 over the entire range of operational conditions (within an error of ±7.5%), 2. a shorter pulse and a longer time interval between the pulses result in a smaller SMD, 3. the SMD may by decreased by some 25%, as compared to a continuous injection, when the pulse time duration reduces to 20% of the total cycle time, and 4. short time pulses and long interval between pulses, are always preferable to produce small droplets.

Cyclic Variability has long been recognized as limiting the range of operating conditions of spark ignition engines, in particular, under lean and highly diluted operation conditions. Previous studies have shown that if cyclic variability could have been eliminated, there would be a 10% increase in the power output for the same fuel consumption. The cyclic variability results also in high level of variations in the engine speed which is interpreted as poor driveability. At full load, some of cycles tend to knock, while other may not have complete combustion by the time the exhaust valve opens. An experimental study has been performed in order to evaluate the relative contribution of several relevant parameters on the cyclic variability in spark ignition engines. The cyclic variability has been examined via five major different pressure-related identifier, i.e. Pmax, θPmax, IMEP, (dp/dθ)max and θ(dp/dθ)max.

Cycle variability in spark-ignition engines is mainly attributable to the occurrence of poor ignited and misfired cycles. The non-ordinary ignited cycles were previously observed to occur when either, the flame did not move away from the electrodes, and therefore had much contact with electrodes, or when large portions of the flame were rapidly convected away from the electrodes and therefore the flame was quenched in the flow field. Cycle variability can also occur due to turbulence or non-homogeneity in the mixture strength. Experiments showed that the degree of the cyclic variability depends very much on the characteristics of the introduced spark, the flow regime in the electrodes' gap, and the spark plug design. In the present work, we investigated the effect of the amount of energy supplied to the spark plug, the law of energy deposition during glow phase, the mean velocity vector in the spark gap and the spark plug orientation, on the mixture lean misfire limit.

The crankcase-scavenged two-stroke-cycle engine is preferred in cases where low weight and high power output are paramount requirements. These qualities are most important in small pilotless aircraft. It was found that the main problem in the use of two-stroke cycle engines for this purpose, is a sharp decrease in the engine power with the increase in altitude. This is attributed not only to the low density of the ambient air, but also to the deterioration of the efficiency of the gas exchange process. In order to improve the engine performance at high altitude, it is proposed here to employ a stepped-piston engine. The engine is constructed of a stepped piston and a single stepped cylinder thus forming three compartments; a power, a compression and a crankcase compartment. In this arrangement, the fresh charge is compressed in the compression compartment before it enters the crankcase compartment.

The effect of oxygen-containing additives on the toxic emission of a SI engine, has been studied. The relationship between the chemical structure of the additives, their oxygen content and molecular mass, and the chemical composition of the exhaust gas toxic compounds (CO, HC and NOx), has been established. More than 20 samples of fuel blends containing oxygenates, were tested. The tested oxygenates represent three large chemical structure categories which can be found in the chemical industry wastes - alcohols, ethers and ketones. The tests were performed using a four-cylinder, spark-ignition engine. In order to determine the optimum types of fuel additives for the suppression of carbon monoxide, hydrocarbons and nitro-oxygens, fuel blends containing 10% oxygenates with different oxygen content (from 9% to 50%) and molecular mass (from 32 to 170) were examined.

Cyclic variability has long been recognized as limiting the range of operating conditions of spark ignition engines, in particular, under loan and highly diluted operation conditions. Previous studies have shown that if cyclic variability could have been eliminated, there would be a 10% increase in the power output for the same fuel consumption. The cyclic variability results also in high levels of variation in the engine speed that is interpreted as poor driveability. At full load, some of the cycles tend to knock, while some others may not have complete combustion by the time the exhaust valve opens. The cyclic variability is usually attributed to the result of random fluctuations in equivalence ratio and flow field due to the turbulent nature of the flow in the cylinder.

A new empirical model is presented to simulate the complete performance map of an automotive turbocharger which consists of a radial turbine and radial compressor. Each of these components is modelled by a particular system which includes basic elements such as orifices, diffusers and a head gain unit organized in series or in parallel. This model which is, in particular, practical for detailed computer program of engine simulation may be simply calibrated to reproduce a wide range of experimental performance maps of typical automotive turbochargers. The isentropic efficiency contours of each component have been approximated by a generalized mathematical expression. The relevant constants may be adjusted so as to fit a specific map.

A semi-empirical model is proposed to represent the scavenging process in cross, loop or uniflow scavenged engines. The model is based on the assumption that in most cases (if not in all) the time variation of the mass fraction of fresh air content in the gas passing through the exhaust port (β) exhibits an “S” type curve. An exponential function of the form of is suggested to fit this curve where the shape and the form factors may consider any combination of perfect displacement, perfect mixing and short-circuiting processes. The charging efficiency was then calculated and compared with other models - the isothermal mixing, the non-isothermal mixing, the Benson model and a detailed computer model. The new model has been found as a realistic model for modern engine design and an easy-to-use model for computer simulations.

A theoretical model to simulate the gas exchange process in a two-stroke, cross or loop-scavenged engine is presented. In this model, the geometry of the cylinder and port assemblies, as well as the physical conditions of operation are represented. The mathematical model consists of five conservation laws in quasi 3-dimensional form. These were transformed into a form which both allows the domain of solution always to be confined in the volume occupied by the gas and also fits the geometry of the cylinder ports. The transformed equations were solved numerically by a finite-difference method to yield the instantaneous and spatial distribution of the temperature, gas composition and velocity fields inside the cylinder from which the gas exchange process was characterized. The predictions were compared with some experimental observations obtained from a flow visualization rig and found in good agreement.

The typical convex torque of a simple two-stroke engine having a port-controlled piston is attributed to the backflow through the scavenge ports. It is proposed here to suppress the backflow by installing scroll diodes at the scavenge ports. Experimental observations on a fired engine demonstrate the remarkable improvement achieved with the diodes installed. The effect of the diodes presence on the engine power and on the delivery ratio is discussed by using a recorded diagram of the crankcase pressure variation with crank-angle during the gas exchange process.

An improved mathematical model is presented here to simulate the gas exchange of a two-stroke, cross or loop-scavenged engine. In this model, the geometry of the cylinder and port assemblies, as well as the physical conditions of operation are fully represented. The basic model which was described by the present author in a former work, has been modified here to include the Woolley-Hatton model for turbulent flow. By comparing predictions from both models with experimental measurements, it seems that a significant improvement was achieved here in predicting the instantaneous interface profile between the incoming charge and the burnt gas.