Different Methods of Knock Detection and Knock Control

<div class="htmlview paragraph">This paper will explore the knock and emissions control capabilities of the Lucas Adaptive Ignition System.</div> <div class="htmlview paragraph">A detailed description is given of the operation of the adaptive knock control together with its integration with efficiency seeking control. Comparisons are made between the performance of adaptive and conventional knock control strategies.</div> <div class="htmlview paragraph">Results are presented on the ability of the adaptive ignition system to control the trade-off between NOx and fuel consumption on a number of vehicles. Operation on lean burn engines will be studied with particular reference to the influence of adaptive ignition on the lean and rich limits of operation.</div> <div class="htmlview paragraph">Suggestions are made on the simplified application strategy for the adaptive ignition system.</div>

<div class="section abstract"><div class="htmlview paragraph">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. Results demonstrate that the analyzed methods give quite similar outcomes but they also highlight that AR and DWT techniques present an higher sensitivity for soft knock detection. Moreover, both AR model and DWT based method may be applied to the engine block vibrational signals, acquired by low-cost accelerometers. Therefore, they can be implemented within modern on-board control units, in order to execute a real time knock detection allowing to realize more sophisticated spark advance control strategies.</div></div>

<div class="htmlview paragraph">Motor fuels are today increasingly blended with oxygenate components to reduce global CO<sub>2</sub> emissions. Among these components, biomass-derived ethanol is very popular for spark ignition engine operation as it is not only a renewable source of energy, but it also allows to increase the engine power and thermal efficiency. Indeed, ethanol has the advantage of a high latent heat of vaporization leading to the so-called “cooling effect” which allows to increase the air-mass flow rate in the engine while reducing the charge temperature. This last property of ethanol combined with its high octane index make the engine less sensitive to knock. Then, although ethanol is characterised by high combustion speeds, optimal values of spark advance can be maintained on a larger range of engine operating conditions and high compression ratios as well as increased levels of downsizing can be used, all these aspects contributing to improve fuel consumptions.</div> <div class="htmlview paragraph">However, the real potential of ethanol blended fuels still has to be explored and their impact on engine control strategies has to be investigated, especially considering the possible fuel composition variability during the engine life. Both issues can nowadays be addressed at low cost using system simulations of the whole engine, provided that the models used correctly account for the effect of the fuel composition on combustion processes.</div> <div class="htmlview paragraph">This paper deals with the extension of a 0-dimensional coherent flame model to the combustion of ethanol blended gasoline for the simulation of heat release, knock and pollutants in SI engines. This extension mainly relies on the combination of a new laminar flame speed correlation, a modified set of chemical reactions in the flame front and an adapted correlation for the knock delay. The proposed developments are validated on a wide experimental database including many engine operating conditions as well as ethanol volume fractions ranging from 0% to 30%. Parametric variations in terms of spark advance and fuel/air ratio are also performed to compare optimal engine settings obtained from the simulations and at the engine bench. A good agreement is observed, showing the interest of using system simulations to predict the influence of the fuel composition on SI engines operation.</div>

<div class="section abstract"><div class="htmlview paragraph">All internal combustion piston engines emit solid nanoparticles. Some are soot particles resulting from incomplete combustion of fuels, or lube oil. Some particles are metal compounds, most probably metal oxides. A major source of metal compound particles is engine abrasion. The lube oil transports these abraded particles into the combustion zone. There they are partially vaporized and ultrafine oxide particles formed through nucleation [<span class="xref">1</span>]. Other sources are the metallic additives to the lube oil, metallic additives in the fuel, and debris from the catalytic coatings in the exhaust-gas emission control devices. The formation process results in extremely fine particles, typically smaller than 50 nm. Thus they intrude through the alveolar membranes directly into the human organism. The consequent health risk necessitates a careful investigation of these emissions and effective curtailment.</div><div class="htmlview paragraph">Substantial information is available on diesel engine particulate emissions [<span class="xref">2</span>, <span class="xref">3</span>, <span class="xref">4</span>] but less for SI engines. Beside an example of metal oxide particles from a diesel engine, the present paper shows preliminary results of nanoparticles emissions of SI engines.</div><div class="htmlview paragraph">Four SI engines were investigated: two older and two newer engines, comprising two car engines and two motorbikes. The tests were done on standard transient driving cycles, and steady-state at constant 50 km/h and idling. Prior investigations observed, especially during idling, high concentrations of metal oxide particles [<span class="xref">2</span>]. All tests were done with particle samples collected from the CVS tunnel, during a long operating period, to have sufficient material for analyzing the composition. At the steady-state points, the particle size spectra were measured.</div><div class="htmlview paragraph">The results show that the older SI engines emit high concentrations of soot particles and metal oxide (= ash) particles. The size distribution is decisively bimodal for both soot and ash particles.</div><div class="htmlview paragraph">The newer engines' emission results are less uniform and the concentrations lower, as expected. Altogether, the concentrations of these metal oxide particles are so high, that more detailed investigations are recommended.</div></div>

<div class="section abstract"><div class="htmlview paragraph">This study meticulously examines the ignition coil (IG), a pivotal component in engine operation, which transforms the low voltage from the battery into the high voltage necessary for spark plug electrode flashover, initiating the combustion cycle. Considering the importance of IG coils in engine operation which has a direct impact on the engine performance. Any failure in the IG coils is judged as a critical failure and encompasses severe repercussions.</div><div class="htmlview paragraph">The paper details an investigation into the issue of ‘White Deposition’ on IG coils. White deposit was observed in IG Coils during new model development in bench level durability test. A comprehensive failure analysis was conducted, employing vibration analysis, thermal analysis, and chemical analysis of the white deposits to ascertain the root cause. Subsequent to identifying the root cause, the study elaborated on hardware design enhancements as a solution. These design changes were rigorously tested on engine benches, confirmed for efficacy, and have been successfully implemented to address the issue.</div></div>

<div class="htmlview paragraph">As we developed Ion Current Combustion Control system (ICCS), we began to discover some issues of the ion current system. Depending upon combustion scenarios, the noise contributed to weak output characteristics and output variations making the combustion unstable.</div> <div class="htmlview paragraph">This paper intends to present methods developed to overcome these issues:</div> <section id="s_1" class="section"> <h2 class="title">SYSTEM HARDWARE</h2> <div class="htmlview paragraph">In the previous report<sup>(<span class="xref">1</span>)</sup>, we described the issues on the detection sensitivities and noise proof characteristics. In this study, we further reviewed the system component designs to address those challenges.</div> </section> <section id="s_2" class="section"> <h2 class="title">SYSTEM SOFTWARE</h2> <div class="htmlview paragraph">We have reported<sup>(<span class="xref">1</span>)</sup> a learning method for the stable knock control for varying output characteristics. However, there was a limitation in the application. Hence, we further analyzed the ion current characteristics, then developed a new algorithm to resolve this issue. This new system with the knock control and the misfire detection was introduced in 2000 MY.</div> </section>

<div class="section abstract"><div class="htmlview paragraph">This paper seeks to examine the effect of distance of the gas injector from an inlet valve on the combustion process in a LPG fuelled SI engine under varied injection timing. Tests were conducted at an engine test stand, where the operating conditions of the engine were maintained stable. The tests were undertaken on an indirect injection spark ignition engine under partial load and at a constant speed. Holes in the inlet pipes were drilled in order to test for four variants of injection nozzle distance from the combustion chamber into which 4 mm diameter nozzles were successively mounted. Each given distance was measured along the symmetry axis of the inlet port, which represents a real path of the fuel-air mixture.</div><div class="htmlview paragraph">The results show that the engine performance is affected more by the injector distance from the inlet valve than by varied LPG injection timing. Consequently, cycle-to-cycle variations of main combustion parameters and engine performance parameters were analyzed. The results show that the distance between the injection nozzle and the combustion chamber affects the unrepeatability of engine operation. To evaluate the cycle-to-cycle variations of the combustion parameters, the coefficient of variation (COV) and return maps of the IMEP were calculated for each engine operating condition. The increase of CO and HC emission were recorded in some cases because of the nozzle distance impact on combustion. The maximum distance between the nozzle and the inlet valve caused a significant increase of hydrocarbon in exhaust gases.</div></div>

<div class="htmlview paragraph">The production unit number of small diesel engine cars tends to decline except recreational vehicles in Japanese market in recent years, while the production unit number in Europe market keeps on increasing owing to the merits of the durability and the fuel consumption. The small diesel engines will have to be improved in the near future by solving major problems such as noise and vibration pollution, environmental pollution, improvement in performance of diesel engines, in order to expand the production of the engines.</div> <div class="htmlview paragraph">This paper refers to a basic study on the experimental and analytical methods for the reduction of resonant vibration in each vibration mode on some cylinder blocks of small high-speed diesel engines in rated engine speed range. Hammering test method, which is easy and useful for measuring frequency response functions, is carried out in the experiments. In this test, the cylinder blocks are directly excited with the impulse hammer, and more the main journals are excited via the newly-made force transmission parts in the next experiment. Two kinds of the engines which have been recently recognized as low noise and vibration engines are chosen in this study. The cylinder blocks of the engines are called of long skirt type and ladder frame type, respectively. The vibration characteristics of these cylinder blocks are obtained in the frequency range from 500 <i>Hz</i> to 2 <i>kHz</i> using the experimental modal analysis. This frequency range is chosen in consideration of the reliability of the vibration experiments. And the force transmission routes from the piston heads to the crank journals of each cylinder block are considered as mentioned in the latter experimental method. The experimental results are used to calculate the natural frequencies by the modal analysis and the calculated results are compared with the ones obtained from FEM analysis. Furthermore, the cylinder blocks are remodeled in order to reduce the vibrations of all modes using FEM analysis.</div> <div class="htmlview paragraph">Consequently, it has been shown that the vibration stress of the cylinder block can be reduced by higher rigidities and more lightening weights of the crankcase and the crank journals in the measured frequency range.</div> <div class="htmlview paragraph">The conclusions are described as follows;</div> <div class="htmlview paragraph"> <ol class="list nostyle"> <li class="list-item"> <span class="li-label">1</span> <div class="htmlview paragraph">The hammering test method using the force transmission parts is useful to measure the natural frequencies of a cylinder block. This method can be easy to get the equal results with the measured ones on running conditions without engine operation.</div> </li> <li class="list-item"> <span class="li-label">2</span> <div class="htmlview paragraph">The hammering test method using the force transmission parts can easily analyze the natural frequencies at all the vibration modes on equal conditions with running ones. Then the method is a useful tool for improving the vibration characteristics.</div> </li> <li class="list-item"> <span class="li-label">3</span> <div class="htmlview paragraph">It has been proved from the analytical viewpoints that the cylinder block of the ladder frame type can be adopted as low-noise, small diesel engines with little increase of the engine weight while maintaining higher rigidity.</div> </li> </ol> </div>

<div class="htmlview paragraph">The impact of the new unleaded fuel qualities with significantly altered Octane numbers and new European emission standards on design philosophy of gasoline engines is discussed.</div> <div class="htmlview paragraph">The design features of a new engine family show how the introduction of unleaded fuels has influenced engine concepts for the European market. The technologies which have become necessary and possible (catalytic emission control) for these concepts are mentioned. The difference between present European design concepts and future demands is shown.</div> <div class="htmlview paragraph">A detailed presentation including development results demonstrates that the VW concept with knock control and fuel injection has a wide range of fuel tolerance. The advantages and main areas of application of concepts which include knock control are explained.</div>

<div class="htmlview paragraph">The fuel direct injection in SI engines is demonstrating a remarkable potential regarding the reduction of consumption and pollutant emission. Nevertheless, the management of the mixture formation “in-cylinder” - in conditions of a short duration and of a complex fluid dynamic configuration imposes both an accurate modeling and an exact control of the process.</div> <div class="htmlview paragraph">The problem gains on complexity when considering the use of alternative fuels which becomes more and more a subject of actuality.</div> <div class="htmlview paragraph">The paper presents a comparative analysis of mixture formation process and engine performances, when applying direct injection of gasoline, respectively of ethanol in a four-stroke single cylinder SI engine. The modulation of the injection rate shape is the result of a fuel high pressure wave, generated in a pressure pulse direct injection system.</div> <div class="htmlview paragraph">The internal mixture formation is modeled in base on the CFD code FLUENT, allowing the analysis of the space-and time-related process sequences for both fuels, using different parameter combinations for injection system and engine.</div> <div class="htmlview paragraph">The comparison of both fuels at the test bench of the injection system is made for different injection volumes, injection frequencies and injector opening pressures. A spray visualization for the most representative configurations is presented as well.</div> <div class="htmlview paragraph">Finally, the engine results at the test bench confirm the good adaptability of the applied direct injection concept for both gasoline and ethanol application.</div>

<div class="section abstract"><div class="htmlview paragraph">The paper presents a combined experimental and numerical activity carried out to improve the accuracy of conjugate heat transfer CFD simulations of a high-performance S.I. motorbike engine water cooling jacket. The computational domain covers both the coolant jacket and the surrounding metal components (head, block, gasket, valves, valve seats, valve guides, cylinder liner, spark plug).</div><div class="htmlview paragraph">In view of the complexity of the modeled geometry, particular care is required in order to find a tradeoff between the accuracy and the cost-effectiveness of the numerical procedure. The CFD-CHT simulation of water cooling jackets involves many complex physical phenomena: in order to setup a robust numerical procedure, the contribution of some relevant CFD parameters and sub-models was discussed by the authors in previous publications and is referred to [<span class="xref">1</span>, <span class="xref">2</span>, <span class="xref">3</span>, <span class="xref">4</span>].</div><div class="htmlview paragraph">Among the formers, the effects of a proper set of boundary conditions and a detailed representation of the physical properties of the involved materials were evaluated. Among the latter, the contribution of a two-phase approach taking into account the effects of phase transition within the engine coolant was considered.</div><div class="htmlview paragraph">The CFD-CHT setup is now applied to investigate and understand the origin of a critical engine behavior occurring at the engine test bench under a severe reliability test. Additional sub-models are introduced and their impact on the results is discussed. Different engine operations are modeled and a detailed analysis of the many thermo-mechanical factors influencing the engine fatigue strength is carried out.</div><div class="htmlview paragraph">At the end of the process, CFD simulations are able to correctly capture and understand the origin of the engine failure, thus leading to a faster and more effective design modification.</div></div>

<div class="section abstract"><div class="htmlview paragraph">With progressing electrification of automotive powertrains and demands to meet increasingly stringent emission regulations, a combination of an electric motor and downsized turbocharged spark-ignited engine has been recognized as a viable solution. The SI engine must be optimized, and preferentially downsized, to reduce tailpipe CO<sub>2</sub> and other emissions. However, drives to increase BMEP (Brake Mean Effective Pressure) and compression ratio/thermal efficiency increase propensities of knocking (auto-ignition of residual unburnt charge before the propagating flame reaches it) in downsized engines.</div><div class="htmlview paragraph">Currently, knock is mitigated by retarding the ignition timing, but this has several limitations. Another option identified in the last decade (following trials of similar technology in aircraft combustion engines) is water injection, which suppresses knocking largely by reducing local in-cylinder mixture temperatures due to its latent heat of vaporization. Addition of adequate water can lead to stoichiometric air/fuel ratio engine operation, and hence both reduction in fuel consumption and full utilization of a three-way catalytic converter (TWC).</div><div class="htmlview paragraph">Further information about effects of various water injection parameters is required. Thus, in this study, a 4-stroke, 1.5 liter, 3-cylinder turbocharged engine with direct fuel injection and port water injection was operated on 91, 95 and 98 RON gasoline fuel to assess effects of water injection on knock mitigation, combustion phasing, required air:fuel ratios and exhaust gas temperature control. Full- and part-load curves obtained with different fuels and water injection strategies are presented and discussed.</div></div>

<div class="section abstract"><div class="htmlview paragraph">In many Asian countries a significant automobile market share is held by two and three wheelers. Generally, cost and simplicity considerations limit the performance and emission levels of small engines. Methanol is an excellent alternative fuel for SI engines due to its high-octane number, high flame speed, presence of oxygen in its molecule and thus can be used to enhance the performance of small engines. However, use of neat methanol in SI engines poses constraints due to low energy density and poor vaporization characteristics. Also, the effectiveness of methanol as a fuel has still to be thoroughly investigated in small-bore SI engines in order to assess its potential.</div><div class="htmlview paragraph">In this work, a small-bore 200cc three-wheeler automotive engine was modified to operate in the port fuel injection mode with neat methanol as the fuel. Experimental studies on the engine were conducted initially at different loads at stoichiometric conditions and performance, combustion and emissions were compared with operation on gasoline under similar conditions. The effect of air fuel ratio was also studied with the two fuels in order to identify the prospects of operating the engine with lean mixtures. The engine showed improved brake thermal efficiency and lower CO<sub>2</sub>, THC, and NOx emissions with methanol as compared to gasoline. The combustion characteristics including cycle by cycle variations have also been compared. Detailed experimental results are presented and discussed in this paper.</div></div>

<div class="htmlview paragraph">The problems of Two-Stroke SI engines regarding high fuel consumption and unburned hydrocarbon emissions, both caused by the short circuiting of fresh homogeneous mixture during the scavenge process, are well-known. The progress of Piaggio since 1977 in state-of-art direct fuel injection systems, oriented to development of Hi-Tech solutions for 2T SI engines to overcome the above drawbacks, is analyzed.</div> <div class="htmlview paragraph">The analysis includes several streams of research ranging from conventional crankcase scavenged engines with direct solid mechanically controlled fuel injection to solutions with separate scavenging pump with electronically controlled injection units, and from low pressure injectors to air-assisted fuel injection with stratified charge.</div> <div class="htmlview paragraph">Each solution is examined with presentation of typical engine parameters and cost data. The solutions are finally compared using specific drivers related to brake mean effective pressure, brake specific fuel consumption and global energy conversion efficiency.</div> <div class="htmlview paragraph">An original methodology to compare different classes of engines is described and utilized to make the global evaluation easier through a multidimensional point of view.</div> <div class="htmlview paragraph">At the end, the leading philosophy beyond the apparently not well focused research strategy appears very clear. The Piaggio FAST (Fully Atomized Stratified Turbulence) solution, the first mass produced 2T SI engine for vehicle applications, is as the logical conclusion of the twenty years research.</div>

<div class="htmlview paragraph">The effects of engine operating conditions on the octane requirement and the resulting knock-limited output were studied on a single cylinder engine using production cylinder heads. A 4-valve cylinder head with port deactivation was used to study the effect of fuel octane, inlet air temperature, coolant temperature, air/fuel ratio, compression ratio and exhaust back pressure. The effect of the thermal environment was studied in more detail using separate cooling systems for the cylinder head and engine block on a 2-valve cylinder head.</div> <div class="htmlview paragraph">The results of this study compared closely with results found in the literature even though the engine and/or operating conditions were quite different in many cases. Guidelines on the effect of various parameters on the octane requirement of an engine can be summarized as follows:</div> <div class="htmlview paragraph"> <ul class="list disc"> <li class="list-item"><div class="htmlview paragraph">Spark Advance: 1 ON/1° SA</div></li> <li class="list-item"><div class="htmlview paragraph">Intake Air Temperature: 1 ON/7 K</div></li> <li class="list-item"><div class="htmlview paragraph">Air/Fuel Ratio: peaks at 5% rich of stoichiometric, decreases by around 2 ON / air/fule ratio around peak</div></li> <li class="list-item"><div class="htmlview paragraph">Intake Pressure: 3-4 ON/10 kPa</div></li> <li class="list-item"><div class="htmlview paragraph">Compression Ratio: 5 ON/CR</div></li> <li class="list-item"><div class="htmlview paragraph">Exhaust Back Pressure: 1 ON/30 kPa</div></li> <li class="list-item"><div class="htmlview paragraph">Coolant Temperature: 1 ON/10 K (Similar effect of head and block temperature., Larger effect at low speed.)</div></li> </ul> </div>