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Ceramic fibers with high specific surface area and adequate high-temperature strength are commercially available for filtration of diesel particulates and in-situ hot regeneration. The manufacturing of a deep bed filtration medium, using such brittle fibers, became possible after a special knitting technique was developed which forms the loops with minimum friction and pretension. Within this structure, the fibers are very little constrained and expose their active surface almost completely. Hence, high filtration efficiencies in the range of 95% could be demonstrated with favorable back-pressure characteristics. Blow-off phenomena were never observed. Endurance testing on engines, with full-flow burner regeneration, proved the high robustness to mechanical and thermo-mechanical loading. This is one of the particular advantages of the new concept.

Using advanced computer controlled knitting techniques pioneered by Courtaulds, 3-D fibre preforms suitable for Structural Reaction Injection Moulding (S.R.I.M.) can be produced in an automated and highly reproducible manner. Development of these techniques over the last two years has allowed glass, aramid and carbon fibres to be processed successfully. The technique is very versatile and a wide variety of 3-D shapes is possible. For example, a flanged ‘T’-junction preform in glass fibre has been evaluated as a concept component in a Courtaulds S.R.I.M. research programme. Specific preforms have been developed for applications in the automotive, aerospace and general engineering industries. The advantages of these knitted 3-D preforms are reproducibility, high production rates, fibre continuity throughout the structure, zero waste and the ability to mix fibres easily.

Knitted vinyl is produced by slitting calendered polyvinyl chloride film and knitting the resulting “threads” into a material having physical properties characteristic of vinyl upholstery combined with the styling flexibility of textiles. The porosity of the product makes it the most breathable type of supported polyvinyl chloride yet introduced.

A reduction of engine knock intensity is demonstrated by incorporation of a stepped piston top to provide an abrupt increase in flame front area in an ASTM-CFR octane rating engine. The conclusions are based on several different types of knock measurements. Three different piston designs were tested. Decreases in the knock intensity, the magnitude of the pressure oscillations following knock, of up to 40% were realized. The statistical nature of knock is shown to be somewhat different from a normal distribution. The data have more scatter, particularly toward the high side of the mean value.

Knock is an abnormal phenomenon with in-cylinder pressure oscillations, which must be avoided to protect the engine from damage and to avoid excessive noise. Conventional control algorithms delay the combustion with the spark to avoid high knocking rates but reduce the thermal efficiency and restricts the performance of a spark ignition engine. The detection and characterization of low-knocking cycles might be used for improving knock control algorithms, however, it is a challenging task, as normal combustion also excite the different resonance modes and might be confused with knock. Most of the methods found in literature for knock detection use 0-Dimensional indicators, regardless of the angular evolution of the pressure oscillations. In this paper, the in-cylinder pressure oscillations evolution during the piston stroke is analyzed by using various time-frequency transformations.

A general definition and an index for the assessment of different engine knock behavior have been developed. The knock onset locations have been determined by piezoresistive pressure actuators and optical fiber probes in full load engine operation mode. The thermodynamic conditions at the knock onset locations have been quantified by CFD-calculations. Therefore the local fuel concentration, mixture temperature and residual gas concentration have been considered. These calculated thermodynamic conditions were further used to calculate the necessary volume of an exothermal center for the generation of the maximal measured pressure amplitudes.

Experiments were performed to identify the knock trends of lean hydrocarbon-air mixtures, and such mixtures enhanced with hydrogen (H2) and carbon monoxide (CO). These enhanced mixtures simulated 15% and 30% of the engine's gasoline being reformed in a plasmatron fuel reformer [1]. Knock trends were determined by measuring the octane number (ON) of the primary reference fuel (mixture of isooctane and n-heptane) supplied to the engine that just produced audible knock. Experimental results show that leaner operation does not decrease the knock tendency of an engine under conditions where a fixed output torque is maintained; rather it slightly increases the octane requirement. The knock tendency does decrease with lean operation when the intake pressure is held constant, but engine torque is then reduced.

Utilizing the desirable feature of hydrogen, this study demonstrates the improvement of engine performance and exhaust emissions due to the mixing of hydrogen into natural-gas fuel in a spark-ignition engine at the wide-open throttle (WOT) condition. Both hydrogen and natural-gas fuels were injected into the intake port only in the suction flow, which could make the operation under a wide range of conditions without backfire even at a hydrogen fuel. Based on the measured processes of combustion, the knock characteristics were discussed with special attention to the extremely high burning velocity of hydrogen. At a higher compression ratio, the thermal efficiency in the stoichiometric condition was improved, nevertheless a precise control of ignition timing was required to suppress a hard knock. From the experimental results of engine performance in a variety of parameters, optimal use of hydrogen was exhibited for different engine loads.

A rapid compression/expansion machine (RCEM) based on a single-cylinder engine was developed to understand the fundamental phenomenon of knock during spark-ignition (SI) combustion. In order to cause auto-ignition in the end-gas mixture during the flame-propagation process, and also to visualize the processes, the original head of the engine was replaced with a specially designed combustion chamber. The effects of spark timing, compression ratio and equivalence ratio on knock intensity were systematically investigated using the RCEM with n-butane fuel. In addition, the possibility of knock control by the injection of hydrogen into the end-gas region is also discussed. The experimental results indicate that a higher compression ratio, spark-ignition timing at -10 °ATDC and a stoichiometric equivalence ratio cause heavy knock. However, the knock intensity is drastically decreased with hydrogen injection.

The knock characteristics of natural gas (NG), 89 octane unleaded gasoline, 2,2-dimethyl butane (22DMB), and methyl tert-butyl ether (MTBE) in stoichiometric and lean fuel-air mixtures were studied in a production 4-cylinder automotive engine. The Intake Temperature at the Knock Limit (ITKL) was found to be very different for each fuel but in every case the ITKL of lean mixtures was much higher than that of a stoichiometric mixture. Gasoline and 22DMB exhibited a much greater increase in ITKL than MTBE and NG at lean conditions. Surprisingly, for lean mixtures 22DMB exhibited values of ITKL that were much higher than MTBE and almost as high as those of NG. These results are compared with a detailed numerical model of autoignition chemistry. Good agreement between model and experiment is found for all modelled conditions.

In modern turbocharged downsized GDI engines the achievement of maximum thermal efficiency is precluded by the occurrence of knock. In-cylinder pressure sensors give the best performance in terms of abnormal combustion detection, but they are affected by long term reliability issues and still constitute a considerable part of the entire engine management system cost. To overcome these problems, knock control strategies based on engine block vibrations or ionization current signals have been developed and are widely used in production control units. Furthermore, previous works have shown that engine sound emissions can be real-time processed to provide the engine management system with control-related information such as turbocharger rotational speed and knock intensity, demonstrating the possibility of using a multi-function device to replace several sensors.

The different demands with respect to electronic knock control in the USA, Japan and Europe are compared. Available systems to suit the special European requirements of turbocharged and naturally aspirated engines are presented in detail. The influence of the new European emission standards currently under discussion and their effect on the requirements of such systems are considered. Alternative approaches for future systems are discussed.

Today, knock control is part of standard automotive engine management systems. The structure-borne noise of the knock sensor signal is evaluated in the electronic control unit (ECU). In case of knocking combustions the ignition angle is first retarded and then subsequently advanced again. The small-sized combustion chamber of small two-wheeler engines, uncritical compression ratios and strong enrichment decrease the knock tendency. Nevertheless, knock control can effectuate higher performance, lower fuel consumption, compliance with lower legally demanded emission limits, and the possibility of using different fuel qualities. The Knock-Intensity-Detector 2 (KID2) and the Bosch knock control tool chain, based on many years of experience gained on automotive engines, provides an efficient calibration method that can also be used for two-wheeler engines. The raw signal of the structure-borne noise is used for signal analysis and simulation of different filter settings.

The objective of this preliminary investigation was to identify the mechanisms by which knocking combustion cause engine damage. The project was motivated by the need for a knock intensity measurement based on a damage related threshold and not the arbitrary octane-heptane scales. The scope of this work includes a detailed investigation to determine the modes of engine failure resulting from knocking combustion. Using the physical evidence from a collection of knock damaged pistons and other parts, the mechanisms of failure are reconstructed by deductive reasoning. The manner in which knock causes surface erosion, ring fracture, piston land cracking and fracture, piston blow-by and seizure are all addressed. The interrelationships between these various modes of failure are also considered. It is shown that there are two distinctly different aspects of knocking combustion that can initiate damage, namely global heat flux and local pressure-temperature pulses.

The easiest way to identify knock conditions during the operation of a SI engine is represented by the knowledge of the in-cylinder pressure. Traditional techniques like MAPO (Maximum Amplitude Pressure Oscillation) based method rely on the frequency domain processing of the pressure data. This technique may present uncertainties due to the correct specification of some model parameters, like the band-pass frequency range and the crank angle window of interest. In this paper two innovative techniques for knock detection, which make use of the in-cylinder pressure, are explained in detail, and the results are compared with those coming from the MAPO method. The first procedure is based on the use of statistical analysis by applying an Auto Regressive (AR) technique, while the second technique makes use of the Discrete Wavelet Transform (DWT). The data useful for the analysis have been acquired on a high compression ratio four cylinder, spark ignition engine.

An efficient method of detecting engine knock using spectral analysis is presented. Multiple single-point DFTs are used to condition the measured knock signal. Using multiple frequencies in the detection algorithm provides a better signature of the combustion process and enhances the ability to detect low-level knock across the entire operating range of the engine. The detection strategy compares the DFT outputs to a variable reference to determine a knock intensity metric. Unlike currently used techniques, the algorithm adapts the reference (no-knock condition) to varying engine speeds and loads. An overview of the knock detection problem and current technology is presented.

Engine knock has been studied extensively over the years. Its undesired effects on drivability, its potential to damage an engine, and its impact on limiting the compression ratio are the main reasons why it remains a current topic of research. This paper focuses on exploiting the connection between auto-ignition and knock. A new method based on the frequency analysis of the heat release traces is proposed to detect and estimate auto-ignition/knock robustly. Filtering the heat release signal with the appropriate bandwidth is crucial to avoid misdetection. The filter settings used in this paper are found using spectral analysis of the heat release signal. By using the proposed method, it is possible to detect auto-ignition/knock even under the presence of undesired sensor resonance effects and noise from mechanical and electrical sources.

This paper describes a system for knock detection in automobile engines using the spark plug. Operation is based on detection of the effect of the characteristic pressure fluctuations in the cylinder on the conductivity of the slightly ionized combustion gases in the vicinity of the plug gap. A signal processing method is described which gives adequate signal to noise ratio up to high engine speed.

To obtain the maximum output power and fuel economy from an internal combustion engine, it is often necessary to detect engine knock and operate the engine at its knock limit. This paper presents the ability to detect knock using in-cylinder ionization signals on a large displacement, air-cooled, “V” twin motorcycle engine over the engine operational map. The knock detection ability of three different sensors is compared: production knock (accelerometer) sensor, in-cylinder pressure sensor, and ionization sensor. The test data shows that the ionization sensor is able to detect knock better than the production knock sensor when there is high mechanical noise present in the engine.

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.