Engine Knock Margin Estimation Using In-Cylinder Pressure Measurements

Abstract

Abstract-Engine knock is among the most relevant limiting factors in the improvement of the operation of spark ignited engines. Due to an abnormal combustion inside the cylinder chamber, it can cause performance worsening or even serious mechanical damage. Being the result of complex local chemical phenomena, knock turns out to have a significant random behaviour but the increasing availability of new on-board sensors permits a deeper understanding of its mechanism. The aim of this paper is to exploit in-cylinder pressure sensors to derive a knock estimator, based on the logistic regression technique. Thanks to the proposed approach it is possible to explicitly deal with knock random variability and to define the so-called margin (or distance) from the knocking condition, which has been recently proven to be an effective concept for innovative knock control strategies. In a model-based estimation fashion, two modelling approaches are compared: one relies on well-known physical mechanisms while the second exploits a principal component analysis to extract relevant pressure information, thus reducing the identification effort and improving the estimation performance.

Modelagem do fenômeno da detonação aplicada ao motor de combustão flex

“…A autoignição ocorrida dentro da região que ainda não sofreu a queima, gera uma segunda frente de chama. Porém, devido às condições de pressão e temperatura dentro da câmara, esta segunda frente de chama se propaga de forma instantânea, provocando uma onda de choque [2] [3]. Este fenômeno é chamado de detonação ou knock, também sendo conhecida como batida de pino devido ao seu som característico.…”

“…: velocidade de propagação do som dento do cilindro em m/s; A probabilidade da detonação ocorrer cresce na medida em que a pressão de pico dentro do cilindro aumenta até o ponto em que a detonação ocorra em todos os ciclos [3]. Porém, o cálculo da pressão de pico dentro do cilindro é não trivial e está além da modelagem exposta neste trabalho.…”

Engine knock margin control using in-cylinder pressure data: Preliminary results

“…The dashed blocks, represent two additional non-physical systems that are required to properly set the hereby proposed knock control strategy. The knock margin estimation block is based on the approach presented in [14] which is here briefly summarized. The estimation procedure, which uses the incylinder pressure measure, is made up of two steps: the first exploits a Principal Component Analysis (PCA) to extract relevant common features (the eigenpressures) from the pressure traces, in order to reduce the algorithm complexity and to condense relevant information within few variables (γ i , i = 1, .…”

“…For more details the reader is referred to [14]. A stepwise ST test, ranging from 0 to 13 • bTDC, has been used for model identification.…”

“…The knock control strategy proposed in this paper is based on the estimation approach introduced in [14], where the authors build a gray-box model of the knock margin that proves to effectively extract important information from the cylinder pressure traces and describes the knock behaviour in various engine operating conditions, outperforming more traditional physics-based approaches. The estimator provides, for each engine cycle, the knock margin (i.e.…”