Influence of a Combustion Parametric Model on the Cyclic Angular Speed of Internal Combustion Engines. Part I: Setup for Sensitivity Analysis

Abstract

Combustion parameters evaluation presents an important application to engines failures diagnosis. The most extended parametric procedure to describe combustion processes in internal combustion engines is based on the Wiebe's function and depends on the rate of heat release of the fuel (ROHR) and several input parameters. When a combustion model is used for indirect identification and optimization processes, the simulation of both profiles, cyclic pressure and speed, must guarantee an accurate estimation of ROHR through convenient curves estimation. However, in case some input parameters of the combustion model are unknown, several solutions will show up. To fix this problem, a combustion parametric model is proposed. In this work, the necessity of establishing the correlation between the combustion model input parameters, the engine dynamic response (cyclic angular speed), and the interrelation between them, has been demonstrated. This correlation is considered the starting point that will allow the performance of a further sensitivity analysis of the response in terms of combustion, thus optimizing the combustion model in search of unique solutions. The study has been carried out in both a single-cylinder direct-injection (DI) compression ignition engine (CIE) and a threecylinder spark ignition engine (SIE). Data associated to the angular speed profile have been adopted as output parameters of the engine, while combustion-related ones have been considered input parameters. Results showed that, for further sensitivity analysis and model optimization, evaluation of the influence of combustion parameters over the engine angular speed is extremely important, if indirect modeling is applied. The best way to assess the relation between input and output variables is by a sensitivity analysis through a previous design of experiments.

Influence of a Combustion Parametric Model on the Cyclic Angular Speed of Internal Combustion Engines. Part II: Statistical Sensitivity Assessment Results

“…In a few cases, results from IMV identification for input parameters are very accurate (Figures 9 and 10, Tables 3 and 4 in Cruz-Peragón et al). Nevertheless, in most cases, a strategy to improve the method, such as minimizing the number of combustion parameters to be identified by the IMV procedure, is required.…”

“…In a first step, the relation between the instantaneous rate of heat release (ROHR) profile and the instantaneous angular speed is demonstrated. This study was successfully performed in a previous work . Additionally, when indirect methods are applied, the necessity of evaluating the influence of combustion parameters on the engine response (angular speed) to achieve unique solutions is justified.…”

“…The engine test bench included an electric dynamometer attached to a Deutz Dieter LKRS-A single-cylinder DI CIE . Engine behavior makes difficult to perform the linear combinations required in Table .…”

“…A detailed revision about the cyclic profiles provided by both pressure and angular speed modeling can be found in the literature and is summarized as follows: an exponential−based combustion parametric model provides MBF (as described by Wiebe’s function) and calculates ROHR in the combustion chamber by deriving the MBF profile. ROHR can be determined by the measured pressure profile and the First Law of Thermodynamics, considering the chamber as a single homogeneous zone (zero-order model).…”

“…In the second part of the present work, a design of experiments (DoE) is carried out. Experiments have been performed in a test bench with a Deutz Dieter LKRS-A single-cylinder direct-injection compression ignition engine (DI CIE), as mentioned by Cruz-Peragón et al A DM procedure provides the input terms or predictors of the combustion model, while the crankshaft instantaneous angular speed measurements help to establish the output indicators.…”