Jason R. Blough

Analysis of Combustion Knock Metrics in Spark-Ignition Engines

Combustion knock detection and control in internal combustion engines continues to be an important feature in engine management systems. In spark-ignition engine applications, the frequency of occurrence of combustion knock and its intensity are controlled through a closedlooped feedback system to maintain knock at levels that do not cause engine damage or objectionable audible noise. Many methods for determination of the feedback signal for combustion knock in spark-ignition internal combustion engines have been employed with the most common technique being measurement of engine vibration using an accelerometer. With this technique single or multiple piezoelectric accelerometers are mounted on the engine and vibrations resulting from combustion knock and other sources are converted to electrical signals. These signals are input to the engine control unit and are processed to determine the signal strength during a period of crank angle when combustion knock is expected. As the accelerometer detects a number of sources of vibrations in addition to the desired vibration from knock, the signal quality varies significantly from engine to engine, cylinder to cylinder, and over the operating conditions of the engine. To evaluate the effectiveness and accuracy of knock detection via accelerometers, a reference system is commonly employed. One of the most common reference metrics is the signal strength of the combustion pressure over the appropriate frequency range as measured with in-cylinder pressure transducers. This analysis examines both cylinder pressure and accelerometer-based knock intensity metrics, where the pressure-based knock intensity metric is used as the reference measure. Distributions of the knock metrics over a number of engine cycles for various engine speeds, loads, cam timings, and knock levels are measured and fit to a log-normal model distribution. The lognormal model is shown to provide a good fit to the measured distribution and also captures the characteristics of the distribution to include skewness and peakness. In addition the accelerometer intensity metric is correlated to the reference pressure intensity metric. The result of this correlation provides the coefficient of determination, which is used as a measure of the accelerometer intensity metrics ability to indicate knock. The effects of the distribution of the pressure intensity metric on the coefficient of determination are examined by analyzing subsets of the distribution

Accelerometer Based Sensing of Combustion in a High Speed HPCR Diesel Engine

The capability to detect combustion in a diesel engine has the potential of being an important control feature to meet increasingly stringent emission regulations and for the development of alternative combustion strategies such as HCCI and PCCI. In this work, block-mounted accelerometers are investigated as potential feedback sensors for detecting combustion characteristics in a high-speed, high-pressure common rail (HPCR), 1.9L diesel engine. Accelerometers are positioned in multiple placements and orientations on the engine, and engine testing is conducted under motored, single and pilot-main injection conditions. Engine tests are then conducted at varying injection timings to observe the resulting time and frequency domain changes of both the pressure and acceleration signals. The higher-frequency (3 kHz \mL f\ mL 25 kHz) components of the in-cylinder pressure are found to correlate to the peak rate of incylinder heat release and indicated a potential application to the detection of combustion. The accelerometer and pressure signals are analyzed through the use of various functions including angle-dependant fast Fourier transforms (FFT) and coherence to isolate frequency components that are well correlated between the cylinder pressure and accelerometer signals. In addition, these analysis techniques are used to compare the three accelerometer orientations and the individual accelerometer placements.

Dynamic testing of shock absorbers under non-sinusoidal conditions

Abstract This paper deals with the dynamic characterization of an automotive shock absorber, the continuation of an earlier work [1]. The objective of this ongoing research is to develop a testing and analysis methodology for obtaining dynamic properties of automotive shock absorbers for use in CAE-NVH low-to-mid-frequency chassis models. Stepped sine sweep excitation is currently used in industry to obtain shock absorber parameters along with their frequency and amplitude dependence. Sine-on-sine testing, which involves excitation using two different sine waves, has been done in this study to understand the effects of the presence of multiple sine waves on the estimated dynamic properties. In an effort to obtain all frequency dependent parameters simultaneously, different types of broadband random excitation have also been studied. Results are compared with stepped sine sweep tests. Additionally, actual road data measured on different road profiles have been used as input excitation to obtain the shock absorber parameters for broad frequency bands under realistic amplitude and frequency conditions. These results are compared with both simulated random excitation and stepped sine sweep test results.

The effects of different input excitation on the dynamic characterization of an automotive shock absorber

This paper deals with the dynamic characterization of an automotive shock absorber, a continuation of an earlier work [1]. The objective of this on-going research is to develop a testing and analysis methodology for obtaining dynamic properties of automotive shock absorbers for use in CAE-NVH low-to-mid frequency chassis models. First, the effects of temperature and nominal length on the stiffness and damping of the shock absorber are studied and their importance in the development of a standard test method discussed. The effects of different types of input excitation on the dynamic properties of the shock absorber are then examined. Stepped sine sweep excitation is currently used in industry to obtain shock absorber parameters along with their frequency and amplitude dependence. Sine-on-sine testing, which involves excitation using two different sine waves has been done in this study to understand the effects of the presence of multiple sine waves on the estimated dynamic properties. In an effort to obtain all frequency dependent parameters simultaneously, different types of broadband random excitations have been studied. Results are compared with stepped sine sweep tests. Additionally, actual road data measured on different road profiles has been used as input excitation to obtain the shock absorber parameters for broad frequency bands under realistic amplitude and frequency conditions. These results are compared with both simulated random excitation and stepped sine sweep test results. INTRODUCTION The shock absorber is one of the most important elements in a vehicle suspension system. It is also one the most non-linear and complex elements to model. The current method of characterizing the dynamic properties of shock absorbers for CAE models involves testing at discrete frequencies, displacements, and preloads using an MTS test machine. The dynamic stiffness (K) and damping (C) are extracted by fitting a linear model of the form F(ω)=K*x(ω)+C*v(ω) to the measured input displacement (x), velocity (v), and output force (F). The excitation technique is a pure sine excitation at the desired frequency and amplitude. These harmonic excitations are then swept through all desired frequency and amplitudes. Parametric and non-parametric models also exist for the shock absorber. A non-parametric model based on a restoring force surface mapping has been developed [2,3,4]. The model considers the force to be a function of displacement and velocity. Although, this model is more applicable to a single frequency excitation, it serves as a useful tool for identifying the non-linearity’s in the system. A comprehensive physical model was developed by Lang [5], later condensed and validated by Morman [6]. Lang’s model has more than 80 parameters, is computationally complex and is not suitable for comprehensive vehicle simulation studies. Morman’s model has been shown to be useful for studying the effects of design changes for a particular shock. Reybrouck [7] has developed a physical model, which has 14 parameters, valid for frequencies up to 20 Hz, but has limited appeal for the analysis of shock absorbers for NVH applications.

Impingement Identification in a High Speed Diesel Engine Using Piston Surface Temperature Measurements

The objective of this investigation was to identify the impingement event on a diesel piston surface. Eight fast-response, surface thermocouples were installed in one of the pistons of a 2.0 liter, four-cylinder, turbo-charged diesel engine (97 kW @ 3800 rpm). Piston temperatures were transmitted from the engine using wireless microwave telemetry. An impingement signal was identified on the piston bowl lip. A simple parameter for characterizing the impingement event is proposed. The results show an impingement signature at one of the bowl lip thermocouples, under specific operating conditions.

Characterizing the Effect of Automotive Torque Converter Design Parameters on the Onset of Cavitation at Stall

This paper details a study of the effects of multiple torque converter design and operating point parameters on the resistance of the converter to cavitation during vehicle launch. The onset of cavitation is determined by an identifiable change in the noise radiating from the converter during operation, when the collapse of cavitation bubbles becomes detectable by nearfield acoustical measurement instrumentation. An automated torque converter dynamometer test cell was developed to perform these studies, and special converter test fixturing is utilized to isolate the test unit from outside disturbances. A standard speed sweep test schedule is utilized, and an analytical technique for identifying the onset of cavitation from acoustical measurement is derived. Effects of torque converter diameter, torus dimensions, and pump and stator blade designs are determined.

Practical Aspects of Making NAH Measurements

Practical issues to consider when making measurements for Nearfield Acoustical Holography (NAH) analysis are addressed. These include microphone spacing and placement from the test surface, number of microphones and array size, reference microphone number and placement, and filtering of the data. NAH has become an accepted analysis tool so that several commercial packages are available. Its application is limited to test surfaces that are fairly planar, lending itself well to tire testing, front of dash testing, engine face testing, etc. In order to achieve accurate NAH results, the measurement and analysis process must be clearly understood on a practical level. Understanding the advantages and limitations of NAH and the measurement parameters required of it will allow the user to determine if NAH is applicable to a particular test object and environment.

Experimental Investigation of Cavitation Signatures in an Automotive Torque Converter Using a Microwave Telemetry Technique

A unique experimental investigation of cavitation signatures in an automotive torque converter under stall conditions is reported. A quantitative criterion is proposed for predicting early and advanced cavitation in terms of suitable nondimensional pump speeds. The dimensionless pump speed that marks early cavitation is obtained by relating this parameter to the appearance of charge-pressure‐dependent pressure fluctuations in the differential pressure transducer readings. The differential pressure transducers were mounted at well-defined locations in the pump passage of a torque converter. The data were transmitted by a wireless telemetry system mounted on the pump housing. Data were received and processed by a ground-based data acquisition system. Automatic transmission fluid exhibited cavitation for charge pressures of 70‐130 psi and pump speeds of 1000‐ 2250 rpm. Advanced cavitation was marked by operating conditions that exhibited a 2% or more torque degradation from the converter’s noncavitating performance. For a given family of torque-converter designs and a given transmission fluid, the proposed nondimensional pumpspeed criteria are capable of marking early and advanced stages of cavitation for a range of torque-converter sizes and a range of charge pressures in the torque converter.

Cavitation Detection in Automotive Torque Converters Using Nearfield Acoustical Measurements

As automotive torque converters decrease in both diameter and axial length, the effects of cavitation in the torque converter becomes increasingly important on noise, efficiency, and performance goals. Cavitation is the formation and collapse of vapor bubbles in a working fluid when local static pressure falls below the vapor pressure of the working fluid. A technique to detect cavitation in automotive torque converters using nearfield acoustical measurements is presented. The technique concentrates on high frequency noise that is associated with the collapse of vapor bubbles. The nearfield acoustical technique is compared to two other techniques using static pressure measurements inside the torque converter; one on the torque converter stator blades and the other on the torque converter pump blades. A microwave telemetry transmitter was used to obtain data from inside the torque converter in both previous investigations. The nearfield acoustical technique is demonstrated to be valid on a torque converter dynamometer test stand and in the bell housing of an operating vehicle. Using the nearfield acoustical technique, the effects of temperature and charge pressure on cavitation are shown. These effects are shown to agree with typical cavitation behaviors. The results for different performance torque converters are compared in the vehicle and on the dynamometer test stand. The results from in-vehicle tests show the same trends as test stand results. The nearfield acoustical technique provides a simple, relatively inexpensive procedure that can be utilized on a test stand as well as in the vehicle to determine the onset of cavitation in automotive torque converters.

Accelerometer-Based Combustion Metrics Reconstruction With Radial Basis Function Neural Network for a 9 L Diesel Engine

Accelerometer-based combustion sensing in diesel engines has the potential of providing feedback for combustion control to reduce fuel consumption and engine emissions at a lower cost than in-cylinder pressure sensors. In this work, triaxial block-mounted accelerometers were used to measure the engine vibration, and pressure transducers were installed to measure the in-cylinder pressure. The in-cylinder pressure can be further utilized to compute combustion metrics, including the apparent heat release rate (AHR). Engine tests were conducted for various speeds, torques, and start of injections, on a 9 L in-line six-cylinder diesel engine equipped with a common rail high pressure injection system. The relationship between engine block acceleration and AHR was modeled using a radial basis function neural network (RBFNN). By inputting the accelerometer signal to the fixed network, AHR and other combustion metrics were estimated. As the primary concern for radial basis network training is the hidden layer weight vector selection, two algorithms for weight vector selection (modified Gram–Schmidt orthogonalization and principal component analysis) were evaluated by examining the robustness of the resulting network. One-third of the conducted tests were utilized to train the network. The network was then applied to estimate the AHR for the remaining validation tests which were not used to train the network. Comparisons were made based on the combustion metrics estimation results and the selection efficiency among the two weight vector selection methods and the random selection method. Moreover, the capability concerning the networks tolerance for additive noise was also investigated. Results confirmed that the modified Gram–Schmidt method achieved much more accurately estimated combustion metrics with the highest efficiency. On the basis of this study, a real-time closed-loop control strategy was proposed with the feedback provided based on the application of the trained RBFNN.