Search Results

The measured time-history of the cylinder pressure is the principal diagnostic in the analysis of processes within the combustion chamber. This paper defines, implements and tests a pressure analysis algorithm for a Formula One racing engine in MATLAB1. Evaluation of the software on real data is presented. The sensitivity of the model to the variability of burn parameter estimates is also discussed.

A stochastic model for the entire pressure-time history of cycle-by-cycle cylinder pressure variations is obtained by fitting simple parametric models of cylinder pressure development to 506 cycles of continuous experimental data taken at four operating conditions. The cyclic variation is therefore encapsulated in a sequence of cyclically varying model parameters whose statistical properties then complete the stochastic description. Different model forms, (including computationally efficient linearised models), are compared for their degree of fit, and for the ease with which the statistics of the identified parameters can be defined. This approach, which typically accounts for 80-90% of the rms cyclic pressure variation, provides a more complete quantification of the phenomena than previously available, and a basis for simulating statistically identical pressure traces.

This paper deals with the influence of a wall soot layer of varying thickness on the unsteady heat transfer between the fluid and the engine cylinder wall during a full cycle of a four-stroke Diesel engine operation. For that purpose a computational investigation has been carried out, using a one-dimensional model of a multi-layer solid wall for simulating the transient response within the confinement of the combustion chamber. The soot layer is thereby of varying thickness over time, depending on the relative rates of deposition and oxidation. Deposition is accounted for due to a thermophoretic mechanism, while oxidation is described by means of an Arrhenius type expression. Results of the computations obtained so far show that the substrate wall temperature has a significant effect on the soot layer dynamics and thus on the wall heat flux to the combustion chamber wall.

The present study investigated the effects of fluctuation in pressure converted from the piezo sensor output, TDC position and clearance volume on the polytropic index in order to develop an improved method for obtaining pressure diagrams of an engine. The effect of gas leakage from the cylinder was also investigated. The influence of changes in pressure and volume were involved primarily in the sum of the indexes on the compression and expansion sides. Changes in TDC and gas leakage influenced the remainder of the indexes on both sides. These results were confirmed experimentally.

In the paper a new approach to the air standard cycles of piston combustion engines based on the First and the Second Laws of Thermodynamics has been presented. It has been found that a certain entropy increase during the heat addition is required for the cyclic operation of piston engine. It is dependent on compression ratio and may not be neglected while analyzing the air standard cycles. Consequently, compression ratio, amount of heat added to the working gas and the way of heat addition are interdependent. Taking this into consideration an essential theory of piston combustion engines has been developed and the relationships for the efficiencies of air standard cycles have been completed. Also, an air standard cycle of the engine coupled to a turbine and equations for its efficiency have been discussed. The presented analysis leads to more comprehensive insight into engine operation than the methods outlined in the references.

Theoretical thermodynamic analysis reveals that, when a fixed amount of heat energy is added into an Otto cycle the thermal efficiency of that cycle can be substantially improved by increasing the expansion ratio while keeping the compression ratio unchanged to achieve a greater net work output. As such, to maximise the cycle work output, the exhaust gas is allowed to expand to atmospheric pressure within the power machinery itself. With this approach, the pressure versus specific volume diagram of this modified cycle at exhaust valve opening is thus minimised and hence waste heat recovery/utilisation such as the implementation of turbocharging system can be eliminated. This paper presents the development and design considerations of a double helical screw internal combustion engine.

A comprehensive quasi-dimensional computer simulation of the spark-ignition (SI) engine was used to explore part-load, fuel economy benefits of the Variable Stroke Engine (VSE) compared to the conventional throttled engine. First it was shown that varying stroke can replace conventional throttling to control engine load, without changing the engine characteristics. Subsequently, the effects of varying stroke on turbulence, burn rate, heat transfer, and pumping and friction losses were revealed. Finally these relationships were used to explain the behavior of the VSE as stroke is reduced. Under part load operation, it was shown that the VSE concept can improve brake specific fuel consumption by 18% to 21% for speeds ranging from 1500 to 3000 rpm. Further, at part load, NOx was reduced by up to 33%. Overall, this study provides insight into changes in processes within and outside the combustion chamber that cause the benefits and limitations of the VSE concept.

A patented (Reference [1]) new power machine concept has been designed and analyzed for production, and proof of principle subscale tests have been performed, with positive results. The machine design concept is applicable as a compressor, pump, motor, or engine. Simplicity of design based on spherical ball pistons (Figures 1 and 2) enables a low moving part count, high power to weight ratio, elimination of valve train and water cooling systems, and perfect dynamic balance. The new design concept utilizes novel kinematic design to completely eliminate inertial loads that would contribute to sliding friction. Also, low leakage is maintained without piston rings by using a small clearance on the ball piston, resulting in choked flow past the ball. These features provide the potential for an engine with higher efficiency than conventional piston engines.

A zero dimensional combustion model of an axial vane rotary engine has been developed. The engine is a positive displacement mechanism that permits the four “stroke” action to occur in one revolution of the shaft with a minimum number of moving components. Current modeling efforts for this engine require improved estimations of engine parameters such as chamber pressure, chamber wall temperature, gas temperature, and heat loss. The purpose of this investigation was to develop a zero dimensional combustion model that predicts the above-mentioned parameters in a quick and accurate manner for a spark ignition or compression ignition version of the engine. For this effort, NASA's ZMOTTO code was modified. Piston engine data and the results from the modified ZMOTTO code are in good agreement.

Vibration and fatigue study of glass-reinforced nylon, as an alternative material to steel for engine driven fans, is discussed. The use of nylon, which has a lower density than steel, offers a significant weight reduction and consequently less burden on the related underhood components and result in longer life for water pumps, fan clutches and drive belts. The temperature and humidity-dependent properties of nylon fan often works favorably from the view point of fatigue life, by shifting the fan's natural frequencies away from the occurrence of resonance. Nylon fans also offer more design flexibility without significantly affecting the cost. Despite such apparent advantages very little literature in the automotive field has dealt with vibration and fatigue of nylon fans. In this paper, computer-based finite element method (FEA) is used as the analytical tool to determine the frequencies and stresses produced at different values of temperature, humidity, and vibration excitations.

This paper outlines the development process of a radio frequency (RF) plasma ignitor and its application to internal combustion engines. The system features a high Q quarter-wave coaxial cavity resonator that serves as an electric field magnifier and as a discharge device. The preliminary characteristics of the cavity have been studied by the construction and operation of larger scaled devices. Testing has been performed using these devices in a testing apparatus operating under ambient conditions. Once an analysis of the large-scale device is complete, a smaller device, more inclined to interfacing with a standard engine, will be constructed and tested on a full scale engine. The final device is intended to operate in the 800-1500 MHz range.

The frequency of the pressure oscillations caused by spark knock depends on the temperature-dependent speed of sound in the combustion gases. Engine dynamometer tests showed a 6.5% (390 Hz) reduction in the knock fundamental frequency as the air/fuel ratio was swept from 13:1 to 20:1. Engine cycle simulation model predictions of maximum burned gas temperatures correlate well with the data. A robust knock detection system must be insensitive to the range of burned gas temperature (frequency of pressure oscillations) that will be encountered with a particular engine control system operating under the expected range of fuels and environmental conditions.

The use of hydrogen in a spark ignited engine is accompanied by a significant risk for backfire and knock, especially at full load, where the richest mixture is used. In fact, when attempting to maximize engine power, knock can (and usually will) lead to runaway surface ignition and backfire without much delay. Since backfire (and knock) has to be avoided at all cost, an attempt was made to detect and quantify knock from the measured pressure traces. For future use knock detection, combined with multipoint timed hydrogen injection, offers the possibility to avoid backfire by temporarily cylinder deactivation. In a first attempt the standard method using the third derivative of the pressure was tried, but proved to be too insensitive to be of any practical use, even though knock was very audible and the pressure oscillations are easily visible on the measurements. This insensitivity is caused by the very fast combustion achieved with hydrogen, compared to other fuels.

Hydrocarbon emissions during cold start and subsequent engine warm-up constitute the majority of hydrocarbons emitted during an FTP test. Reducing HC emissions during this portion of the test is necessary to meet current and future HC emissions regulations. This paper summarizes the results of a study which quantified the influence of fuel injector configuration and engine calibration on HC emissions prior to catalyst light-off, in a contemporary four-valves-per-cylinder engine. The fuel-injector parameters investigated included dual versus single spray, air-assist versus non-air-assist, and different spray characteristics (cone angle, droplet size). Control parameters investigated included injection timing, air-fuel ratio, and spark timing. Design and calibration merits were assessed according to combustion stability, cumulative hydrocarbon emissions during cold start and warm-up, and catalyst light-off time.

The life of liquid droplets on a hot surface is not a linear function of the surface temperature. Contrary to common belief, targeting the injectors at the intake valves does not always result in the best evaporation of liquid fuel. Timing and targeting of the injectors has to be a function of intake valve surface temperature and opening. This paper will present some guidelines for design of cylinder heads, intake manifolds and injector targeting. Theoretical explanation of the fuel droplet life on the hot surface and its correlation to intake valve deposits and evaporation are discussed. The data presented will support the theoretical guidelines.

Fuel transport was visualized within the cylinder of a port injected four-valve SI engine having a transparent cylinder liner. Measurements were made while motoring at 250 rpm to simulate cranking conditions prior to the first firing cycle, and at 750 rpm to examine the effects of engine speed. A production GM Quad-4 cylinder head was used, and the stock single-jet port fuel injector was used to inject indolene. A digital camera was used to capture back-lighted images of cylinder wall wetting for open and closed intake valve injection. In addition, two-dimensional planar imaging of Mie scattering from the indolene fuel droplets was used to characterize the fuel droplet distribution as a function of crank angle for open and closed intake valve injection. LDV was used to measure the droplet and air velocities near the intake valves during fuel induction. It was found that with open-valve injection a large fraction of the fuel impinged on the cylinder wall opposite the intake valves.

Multi-stage injection diesel spray was investigated to understand the internal flow of a diesel spray. This multi-stage spray consisted of two sprays (we called them the first and second sprays) which were formed by a split injection with a short dwell time. In this paper, we discussed the dynamic behavior of a two-stage injection diesel spray. Especially, we focused on the characteristics of internal velocity and the decay of spray density fluctuation. When the injection rate of a conventional spray increased within an injection period, a spray tip of initially injected fuel was caught up and overtaken by the spray of a following injection. Then the internal structure of a conventional spray greatly depended on the internal spray velocity controlled by the injection rate. Since the second spray penetrated into the first spray, the spray tip motion of the second spray could be considered to be similar to the behavior of an internal spray motion in a conventional spray.

A transient gas jet seems to be a model of a diesel spray because it has no vaporization process. Recently, CNG is utilized in a diesel engine. In the case of diesel engine, sprays or jets have the free state in some cases, and they are impinging surely on the piston surface in the other cases. The 2-D image of acetylene gas with tracer particles was taken by high-speed photography. In both jets, the outer shape was measured on the images and the characteristics of the internal flow was obtained by particle image velocimetry. Then, the physical models of these jets were constructed by use of experimental results.

The behavior of diesel spray impinging on an inclined wall was experimentally investigated in a pressurized vessel. To clarify the wall effect on a diesel spray, a relative angle of the inclined wall to a spray axis was varied. Spray penetration along the wall was observed optically and it was compared with that of a free spray. To evaluate various spray motion quantitatively, a spray path penetration which described a development of a spray tip along the wall was newly introduced. To observe an internal structure of the spray, it was visualized by a YAG laser sheet light and its tomographic image was captured on a film. The photo-image on a film was taken into an image analyzing computer using a high resolved image scanner. A high density zone in the tomographic image was extracted to clarify the internal structure of an impinging spray. The main parameter of the relative position of the wall was its inclined angle which was defined as the angle between the spray axis and wall.

In this study, a new submodel concerning fuel film formation process is proposed in order to simulate the behavior of diesel spray impingement on relatively low temperature wall surface. Here, super - heating degree of the surface, defined by the temperature difference between the wall surface and the fuel saturated temperature, is newly considered for the behavior of impinged liquid droplets. In this spray impingement submodel, fuel film formation process, droplet interaction, film breakup process, and velocity and direction of dispersing droplets were considered based on several experimental results. This new submodel was incorporated into KIVA-II code, and the results were compared with experimental data KIVA-II original code and the spray / wall impingement model proposed by Naber & Reitz. As a result, it is found that the calculated results of impinging spray behavior by the new model agree well with experimental results.