Search Results

An experimental study on flashing injection of gasoline-dissolved CO2 mixtures through specially designed injectors was performed. The injectors used comprised an expansion chamber, prior to the discharge orifice, in order to promote the CO2 flashing. Malvern Mastersizer-X was used to measure the spray characteristics. High-speed digital video camera was employed to visually register the expansion chamber flow patterns. The geometry of the expansion chamber was optimized to produce minimum SMD. The high-speed camera photographs, have revealed the different flow regimes inside the expansion chamber under different operation conditions, and thus provided a solid ground to explain the relationship between the optimal chamber dimensions, the operation conditions, and the observed characteristics of the spray.

When the relative contribution of an individual cylinder to the engine output is different from its counterparts, the engine is operating under non-balanced conditions. This may cause power deterioration, higher fuel consumption and excessive engine emissions in the short term, and a mechanical damage breakdown in the long term. To improve the engine quality, there is a strong need for information concerning the imbalance between the cylinders. This can be used as data for a closed-loop control system to manage the amount of fuel injected to each individual cylinder, or may provide useful diagnostic information concerning a possible developing problem that may lead to an engine failure. Direct measurements of the combustion pressure signal can provide the required indication for the imbalance. It however needs a special-purpose transducer and an intrusive approach to the cylinder, and therefore, can be hardly considered as a good candidate for this purpose.

Imbalance between cylinders is a major concern of a proper operation of reciprocating engines. An engine reliability and performance envelop, including life span, fuel consumption and emission, are strongly affected by an improper operation of the cylinders. To improve the engine quality, there is a strong need for a closed-loop control system to manage the amount of fuel injected to each individual cylinder. An advanced system to detect imbalance related faults in reciprocating engines which is based on the analysis of the engine's mechanical vibrations have been developed. The system is based on a firm theoretical background that provides a fundamental relation between the engine's vibration pattern and the relative characteristics of the combustion process in the different cylinders. With a single accelerometer mounted on the engine's block, online information related to the combustion process in each cylinder is provided by the system.

A high-pressure fuel injector has been designed to produce a spray having a lower SMD than that obtained typically with a common-rail fuel injection system for the same injection pressure. In the present design, a mixture of fuel and dissolved gas (CO2 or N2) is introduced continuously to an injector unit. The downstream part of the injector consists of an inlet orifice, an expansion chamber, a swirl duct, and a discharge orifice. When the mixture enters the expansion chamber, a part of the dissolved gas is transformed into tiny bubbles that grow inside the expansion chamber. When the mixture is discharged through the discharge orifice, these bubbles undergo a rapid flashing process while the liquid bulk disintegrates into small droplets. In the present work, we investigate experimentally the effect of the design parameters (geometrical proportions and injection pressure) on the SMD and cone angle of a continuous spray.

Vibrations analysis methods are common as fault detection and diagnosis tools for rotating machines. The successful implementation of this method in various maintenance programs motivates its application to the class of SI engines. In this work, our goals in applying the method are to provide alerts for abnormal operation, to enable detection of the source of the abnormality, and to provide the means to estimate the severity of malfunctions evolving in the engine. Experiments were performed with a four-stroke, four-cylinder in-line, carbureted SI engine. The vibrations were measured at two points around the rear crankshaft bearings in addition to two opposing points on the sides of the engine-block. At each point the vibrations were measured along the axial, the radial and the tangential directions relative to the crankshaft axis.

Previous investigations have demonstrated that improvements in gasoline engine performance (engine efficiency, power, exhaust emissions, engine braking, and usable engine speed range) can be accomplished if the valve timing are variable. Because of the difficulties of providing a variable valve timing (VVT) mechanism with acceptable cost, durability and reliability, very few automotive engines in normal production have been equipped till now with variable valve timing. However, owing to recent technology developments associated with electromagnetic and hydraulic valve control, and owing to recent progresses in microprocessor utilization, the application of VVT in the near future is quite feasible. In this work valve timing strategies for maximizing engine torque in terms of the intake closing and exhaust opening timings of a commercial throttled SI engine are studied.

Advanced engine maintenance programs incorporate various methods for monitoring the engine parts so as to be able to foresee malfunctions and interruptions of normal operation. The present study is concerned with the development of a vibration signature analysis method for early fault detection and diagnosis in internal combustion engines. The successful implementation of this simple and straightforward method in many maintenance programs motivates the application of this method to the class of SI engines. An acceleration transducer is mounted on the engine and the vibration signals are recorded during the engine operation. The measurements are then transformed to the frequency domain where the frequencies and the amplitudes of the harmonic components of the vibrations waveform are analyzed and compared to the corresponding vibration signature under normal operation conditions.

Catalytic converters appear to be the most effective means to reduce air pollution from internal combustion engines. The conversion efficiency, however, depends very strongly on the working temperature. The efficiency of a precious metalcontaining catalyst, for example, declines very steeply for a temperature of below around 350°C, and the conversion efficiency is practically zero for cold engines (starting and warming-up period). Preheating of the catalyst with an electrical power, warming it up with an external combustion chamber, and installation of an auxiliary small capacity catalytic converter, are some of the more successful solutions. Although these methods are quite effective, all employ active means that require an external energy source and a control unit. In the present work, the exploitation of thermal capacitance to keep the catalyst temperature high during a short parking period was studied.

A simple yet reliable method to evaluate the overall friction power of an internal combustion engine is proposed. The method is based on the measurement of the angular deceleration of the engine speed. The tested engine is coupled to a flywheel having a known high moment of inertia, fired and accelerated to a high engine speed. The system is kept running until steady conditions are attained. Then, the ignition system is shut-off, and the engine speed deceleration vs. time, α, is recorded. The total friction-mean-effective-pressure, tfmep vs. time, may then be evaluated from the fundamental relationship between the two (tfmep=2πIα/Vd, where, Vd is the engine displacement volume, and I is the moment of inertia of the integrated system). The proposed method, is a modification of the direct motoring method, in which the engine is motored by an external means under conditions as close as possible to firing.

The effect of atmospheric pressure on the performance characteristics of a crankcase-scavenged spark-ignition two-stroke cycle engine has been investigated. An air-borne, 350 cc opposed 2-piston engine was tested on an experimental test bench where both the pressure at the inlet manifold and the pressure at the exhaust pipe were controlled separately. The experimental results were analyzed by using a computer program, the MICE Program, which simulates in detail the various processes occurring inside the cylinder of an internal combustion engine. The computer program has been calibrated by using the measured results at sea-level. An empirical correlation has been proposed for the correction factor of the engine power in the range of 100 to 44 kPa, where the low pressure corresponds to a standard altitude of 21,000 ft (7 km).

A new spark plug design in which the spark discharge is preceded by a corona wind is studied. The plug electrodes are designed so as to produce a corona wind whenever a high voltage (but lower than the breakdown voltage) is applied. The corona wind carries the ignited mixture away from both electrodes in order to reduce heat loss from the ignited mixture by heat transfer to the electrodes. The new system facilitates the ignition of lean mixtures, and provides an efficient means for increasing ignition efficiency, improving cyclic variation and reducing HC emission. High speed photographs of the ignition process of the new system in a constant volume bomb have shown that the ignited mixture is carried out from the electrode gap at a speed of 5 m/s; a speed which has been found to be optimal in other studies. Preliminary studies with a conventional 4-cylinder engine have clearly shown promising results.

An effective and simple method to improve the performance of a crankcase-scavenged two-stroke engine under off-design conditions is to reduce the fuel loss, due to short-circuiting, by controlling the pressure at the exhaust port. The present work presents a systematic study of the effect of throttling the exhaust pipe as a means of improving the torque, fuel consumption and emission in a two-stroke-cycle engine. The experimental observations were analyzed and extrapolated with the aid of a detailed computer program which simulates the engine cycle. It was concluded that: 1. The hydrocarbon emissions are significantly reduced when an exhaust contraction is applied. A reduction of 28% may be achieved at a wide range of engine speeds and loads, without a noticeable deterioration in die operation stability. 2. An optimum contraction ratio for HC emission has been observed and was found to be a complex function of the engine speed and load, but mainly dependent on the engine load. 3.

This paper describes the development of a high-efficiency compressed gas source, which can facilitate considerable savings of fuel and energy. This development was achieved by replacing the conventional lay-out, consisting of an internal combustion engine driving a gas compressor, by an internal combustion engine, in which exhaust gases serve as the compressed agent. This approach entailed some changes in the kinematics and structure of the engine: an auxiliary valve had to be added next to the exhaust valve so that the gas remaining in the clearance volume could be discharged to the atmosphere before the intake stroke was executed. A detailed theoretical analysis was applied to optimize the timing of the exhaust valve. An experimental rig was then constructed and tested, and preliminary conclusions were drawn. Such an engine, having an exhaust back pressure as the load (instead of a mechanical load on the crankshaft) is practical for special applications such as pneumatic hammers.

The scavenging process in the cylinder of a two-stroke-cycle internal-combustion-engines is the most important factor controlling the engine efficiency and performance characteristics. A reliable description model of the gas exchange process may be a powerful tool to the engine designer. To benefit the most, the designer should select the best model for his specific purpose. This paper reviews and assesses many scavenging models which have been proposed in the literature for the past three decades. The scavenging models were divided into three categories: One-phase, Multi-zone and Hydrodynamics models and each model has been analyzed for its basic assumptions and prediction ability.