Robert Kee

Two-wire thermocouples: A nonlinear state estimation approach to temperature reconstruction.

The problem of measuring high frequency variations in temperature is described, and the need for some form of reconstruction introduced. One method of reconstructing temperature measurements is to use the signals from two thermocouples of differing diameter. Two existing methods for processing such measurements and reconstructing the higher frequency components are described. These are compared to a novel reconstruction algorithm based on a nonlinear extended Kalman filter. The performance of this filter is found to compare favorably, in a number of ways, with the existing techniques, and it is suggested that such a technique would be viable for the online reconstruction of temperatures in real time.

Difference equation approach to two-thermocouple sensor characterization in constant velocity flow environments

Thermocouples are one of the most popular devices for temperature measurement due to their robustness, ease of manufacture and installation, and low cost. However, when used in certain harsh environments, for example, in combustion systems and engine exhausts, large wire diameters are required, and consequently the measurement bandwidth is reduced. This article discusses a software compensation technique to address the loss of high frequency fluctuations based on measurements from two thermocouples. In particular, a difference equation (DE) approach is proposed and compared with existing methods both in simulation and on experimental test rig data with constant flow velocity. It is found that the DE algorithm, combined with the use of generalized total least squares for parameter identification, provides better performance in terms of time constant estimation without any a priori assumption on the time constant ratios of the thermocouples.

Project Omnivore: A Variable Compression Ratio ATAC 2-Stroke Engine for Ultra-Wide-Range HCCI Operation on a Variety of Fuels

The paper describes the principal features of Omnivore, a spark-ignition-based research engine designed to investigate the possibility of true wide-range HCCI operation on a variety of fossil and renewable liquid fuels. The engine project is part-funded jointly by the United Kingdoms Department for the Environment, Food and Rural Affairs (DEFRA) and the Department of the Environment of Northern Ireland (DoENI). The engineering team includes Lotus Engineering, Jaguar Cars, Orbital Corporation and Queens University Belfast. The research engine so far constructed is of a typical automotive cylinder capacity and operates on an externally scavenged version of the two-port Day 2-stroke cycle, utilising both a variable charge trapping mechanism to control both trapped charge and residual concentration and a wide-range variable compression ratio (VCR) mechanism in the cylinder head. This approach permits individual control of retained and compression heat as separate inputs to the ATAC combustion process (now commonly referred to as HCCI), an ideal situation which is not possible when attempting to operate a traditional fixed compression ratio, variable valve timing 4-stroke engine in HCCI combustion. The ease of application of the VCR system due to the elimination of poppet valves for gas exchange is fundamental to the concept and this feature is discussed in detail, together with the very wide range of compression ratios that the chosen solution permits (from 10:1 to 40:1 in this initial configuration). In addition to describing the engine and its technologies, test results from its initial operation on 98 RON gasoline are presented, including stable operation at idle load and 450 rpm in true HCCI (i.e. without spark assistance).

A Total Least Squares Approach to Sensor Characterisation

Abstract The use of robust, low-bandwidth sensors makes exhaust gas temperature variations difficult to measure in internal combustion engines. One common solution involves measuring gas temperature using two thermocouples with different time-constants and estimating the time-constants from the resulting signals. This assumes that the ratio of the thermocouple time-constants is invariant and known a priori. In addition they are generally subject to singularities and sensitive to noise. This paper presents a novel total least squares (TLS) difference equation based characterisation method. It makes no such assumption and is potentially superior to existing methods in terms of time-constant estimation accuracy and noise tolerance.

Exploiting A Priori Time Constant Ratio Information in Difference Equation Two-Thermocouple Sensor Characterization

The characterization of thermocouple sensors for temperature measurement in varying-flow environments is a challenging problem. Recently, the authors introduced novel difference-equation-based algorithms that allow in situ characterization of temperature measurement probes consisting of two-thermocouple sensors with differing time constants. In particular, a linear least squares (LS) lambda formulation of the characterization problem, which yields unbiased estimates when identified using generalized total LS, was introduced. These algorithms assume that time constants do not change during operation and are, therefore, appropriate for temperature measurement in homogenous constant-velocity liquid or gas flows. This paper develops an alternative beta formulation of the characterization problem that has the major advantage of allowing exploitation of a priori knowledge of the ratio of the sensor time constants, thereby facilitating the implementation of computationally efficient algorithms that are less sensitive to measurement noise. A number of variants of the beta formulation are developed, and appropriate unbiased estimators are identified. Monte Carlo simulation results are used to support the analysis

Blind Deconvolution for Two-Thermocouple Sensor Characterization

Thermocouples are one of the most popular devices for temperature measurement due to their robustness, ease of manufacture and installation, and low cost. However, when used in the harsh environment found in combustion systems and automotive engine exhausts, large wire diameters are required and consequently the measurement bandwidth is reduced. This paper describes two new algorithmic compensation techniques based on blind deconvolution to address this loss of high-frequency signal components using the measurements from two thermocouples. In particular, a continuous-time approach is proposed, combined with a cross-relation blind deconvolution for parameter estimation. A feature of this approach is that no a priori assumption is made about the time constant ratio of the two thermocouples. The advantages, including small estimation variance and limitations of the method, are highlighted using results from simulation and test rig studies.

Unbiased Thermocouple Sensor Characterisation in Variable Flow Environments

Abstract A novel two-thermocouple sensor characterisation method for use in variable velocity flow environments is described. A difference equation method, recently developed by the authors for constant velocity flow applications, is extended to accommodate variable velocity flows using polynomial parameter fitting on a sliding data window. In particular, by using a novel difference equation formulation the invariance of time-constant ratio with respect to flow velocity is exploited to produce an efficient unbiased and consistent time-constant estimator. Monte-Carlo simulation studies show that the new algorithm outperforms alternatives in the literature without the restrictive requirement of a priori knowledge of thermocouple time constant ratios.

Acceleration Test Method for a High Performance Two-Stroke Racing Engine

This paper describes an inertial dynamometer system which has been applied to the testing of small two-stroke kart racing engines. The dynamometer incorporates a flywheel of appropriate moment of inertia to simulate the mass of a kart and driver. The test procedure involves measurement of the flywheel speed during an acceleration phase resulting from opening the throttle. Calculation of the instantaneous flywheel acceleration corresponding to each engine speed directly gives a measure of the torque and power characteristics. Performance results, including exhaust pressure traces, are presented from a series of tests conducted on a 100 cm3 kart engine. The results are compared with corresponding steady state measurements recorded on an eddy current dynamometer. In addition, the measured results are compared with predictions from a computer simulation.

Drivetrain Effects on Small Engine Performance

Presented is a study that expands the body of knowledge on the effect of in-cycle speed fluctuations on performance of small engines. It uses the methods developed previously by Callahan, et al. (1) to examine a variety of two-stroke engines and one four-stroke engine. The two-stroke engines were: a high performance single-cylinder, a low performance single-cylinder, a high performance multi-cylinder, and a medium performance multi-cylinder. The four-stroke engine was a high performance single-cylinder unit. Each engine was modeled in Virtual Engines, which is a fully detailed one-dimensional thermodynamic engine simulator. Measured or predicted in-cycle speed data were input into the engine models. Predicted performance changes due to drivetrain effects are shown in each case, and conclusions are drawn from those results. The simulations for the high performance single-cylinder two-stroke engine predicted significant in-cycle crankshaft speed fluctuation amplitudes and significant changes in performance when the fluctuations were input into the engine model. This was validated experimentally on a firing test engine based on a Yamaha YZ250. The four-stroke engine showed significant changes in predicted performance compared to the prediction with zero speed fluctuation assumed in the model. Measured speed fluctuations from a firing Yamaha YZ400F engine were applied to the simulation in addition to data from a simple free mass model. Both methods predicted similar fluctuation profiles and changes in performance. It is shown that the gear reduction between the crankshaft and clutch allowed for this similar behavior. The multi-cylinder, high performance two-stroke engine also showed significant changes in performance, in this case depending on the firing configuration. The low output two-stroke engine simulation showed only a negligible change in performance in spite of high amplitude speed fluctuations. This was due to its flat torque versus speed characteristic. The medium performance multi-cylinder two-stroke engine also showed only a negligible change in performance, in this case due to a relatively high inertia rotating assembly and multiple cylinder firing events within the revolution. These smoothed the net torque pulsations and reduced the amplitude of the speed fluctuation itself.

Difference equation sensor characterization algorithms for two-thermocouple probes

The characterization of thermocouple sensors for temperature measurement in variable flow environments is a challenging problem. In this paper, novel difference equation-based algorithms are presented that allow in situ characterization of temperature measurement probes consisting of two-thermocouple sensors with differing time constants. Linear and nonlinear least squares formulations of the characterization problem are introduced and compared in terms of their computational complexity, robustness to noise and statistical properties. With the aid of this analysis, least squares optimization procedures that yield unbiased estimates are identified. The main contribution of the paper is the development of a linear two-parameter generalized total least squares formulation of the sensor characterization problem. Monte-Carlo simulation results are used to support the analysis.