The conjugate gradient method of minimization with adjoint equation is used to solve the inverse problem of estimating the timewise variation of interface conductance between periodically contacting solids, under quasi-steady-state conditions. It is assumed that no prior information is available on the functional form of the interface conductance, except the magnitude of the period. The accuracy of the inverse analysis is examined by using simulated inexact temperature measurements obtained at the interior of the region. Small periods are usually the most difficult on which to perform an inverse analysis. For such cases, the present method is found to be more accurate and stable than the B-Spline approach. 19 refs.

Inverse problem of estimating interface conductance between periodically contacting surfaces

Internal combustion engines produce exhaust gases at extremely high temperatures and pressures. As these hot gases pass through the exhaust valve, temperatures of the valve, valve seat, and stem increase. To avoid any damage to the exhaust valve assembly, heat is transferred from the exhaust valve through different parts, especially the valve seat insert during the opening and closing cycle as they come into contact with each other. In this article, a finite-element method is used for modeling the transient thermal analysis of an exhaust valve. The temperature distribution and resultant thermal stresses at each opening and closing time are obtained. Detailed analyses are performed to estimate the boundary conditions of an internal combustion engine. The model includes exhaust valve, seat, guide, and spring. The analysis continues until a steady-state condition is obtained. In this study, ANSYS is employed for modeling and analysis of the exhaust valve. A methodology is developed for transient the...

Transient Thermal Analysis of Engine Exhaust Valve

This work applied an on-line inverse solution methodology based on the weighting input estimation method to determine the interface contact conductance between periodically contacting surfaces. This method is based on the Kalman filtering technique and a recursive least-squares estimator. This recursive least-squares estimator is weighted by the forgetting factor n and proposed for extracting the unknowns. The weighting technique is essential, since the unknown input is time-varied and has an unpredictable changing status. The superior capabilities of this inverse method are demonstrated in several one-dimension timevarying estimate cases and the proposed algorithm is compared with the conjugate gradient method. Results show that this method has the advantages of stability, fast convergence, good accuracy, and demonstrates that only a few measurement sensors are needed.

Inverse problem of estimating interface conductance between periodically contacting surfaces using the weighting input estimation method

Internal combustion engines generate exhaust gases at extremely high temperatures and pressures. As these heated gases exit through the exhaust valve, the valve and valve seat insert achieve comparable temperatures. To avoid damage, heat is transferred from the exhaust valve to the valve seat insert as they come into contact with each other during the opening and closing cycle. Modern engine management systems regulate the thermal process through coolant and/or airflow rates, fuel injection, and ignition timing, and exhaust gas recirculation contributions to achieve satisfactory tradeoffs between power, emissions, and efficiency for various engine speeds and loads. One of the primary functions of the engine control unit is the prevention and detection of abnormal combustion to prevent severe engine damage. The online estimation of cylinder component temperatures offers an opportunity for greater engine control measures. A nonlinear dynamic thermal model is presented to describe the transient and steady-state phenomena in the engine's cylinder using a lumped parameter resistance-capacitance network. The model prediction of the engine's thermal behavior establishes a foundation to explore thermal periodic contact issues. Representative experimental and numerical results will be presented and discussed.

Thermal Periodic Contact of Exhaust Valves

The problems involving periodic contacting surfaces have different practical applications. An inverse heat conduction problem for estimating the periodic Thermal Contact Conductance (TCC) between one-dimensional, constant property contacting solids has been investigated with conjugate gradient method (CGM) of function estimation. This method converges very rapidly and is not so sensitive to the measurement errors. The advantage of the present method is that no a priori information is needed on the variation of the unknown quantities, since the solution automatically determines the functional form over the specified domain. A simple, straight forward technique is utilized to solve the direct, sensitivity and adjoint problems, in order to overcome the difficulties associated with numerical methods. Two general classes of results, the results obtained by applying inexact simulated measured data and the results obtained by using data taken from an actual experiment are presented. In addition, extrapolation method is applied to obtain actual results. Generally, the present method effectively improves the exact TCC when exact and inexact simulated measurements input to the analysis. Furthermore, the results obtained with CGM and the extrapolation results are in agreement and the little deviations can be negligible.

Inverse heat transfer problem of thermal contact conductance estimation in periodically contacting surfaces

This study experimentally examines the heat transfer across surfaces which contact and separate at regular intervals. The results are presented for the case of low contact pressure, moderate interface temperature, equal contact and separation times during a cycle, and identical materials on either side of the contact interface. The results are presented in two basic areas: 1) the behavior of the thermal contact resistance during the quasi-steady state; and 2) the length of time required for the temperature distribution in the material to approach the temperature distribution observed in the quasi-steady-state condition. The results indicate that the thermal contact resistance should not be considered a constant for contacts of short duration; and that relatively few cycles are required for the temperature distribution in the material to approach that observed in the quasi-steady state.

R. R. Johnson

Papers

Experimental study of the transient heat transfer across periodically contacting surfaces

Experimental results for the quasisteady heat transfer through periodically contacting surfaces