Influence of cyclic cylinder pressure variability in the numerical transfer path analysis of multi-body engine

Practical mechanical systems often operate with some degree of uncertainty. The uncertainties can result from poorly known or variable parameters, from uncertain inputs or from rapidly changing forcing that can be best described in a stochastic framework. In automotive applications, cylinder pressure variability is one of the uncertain parameters that engineers have to deal with when designing and analyzing internal combustion engines. Multi-body dynamics is a powerful numerical tool largely implemented during the design of new engines. In this paper the influence of cylinder pressure cyclic variability on the results obtained from the multi-body simulation of engine dynamics is investigated. Particular attention is paid to the influence of these uncertainties on the analysis and the assessment of the different engine vibration sources. A numerical transfer path analysis, based on system dynamic sub structuring is used to derive and assess the internal engine vibration sources. In order to investigate the cyclic variability of cylinder pressure, a Monte Carlo approach is adopted. Starting from measured cylinder pressure that exhibits cyclic variability, random Gaussian distribution of the equivalent force applied on the piston is generated. The aim of this paper is to outline a methodology which can be used to derive correlations between cyclic variability and statistical distribution of results. The statistical information derived can be used to advance the knowledge of the multi-body analysis and the assessment of system sources when uncertain inputs are considered.