The development of one cycle resolution control strategies and the research at HCCI engines demands an accurate estimation of the trapped mass. In contrast to current methods for determining the mass flow, which are only able to determine averaged values of the flow entering the cylinders, the present paper proposes a methodology based on the in-cylinder pressure resonance. The determination of such frequency allows inferring the cylinder mass with one cycle resolution. In addition, the method permits determining error metrics based on the mass conservation principle. Validation results for a reactivity controlled compression ignition (RCCI) engine equipped with electrohydraulic variable valve timing (VVT) are presented to illustrate the performance of the method.

ElsevierBroatch Jacobi, JA.; Guardiola García, C.; Pla Moreno, B.; Bares Moreno, P. (2015). A direct transform for determining the trapped mass on an internal combustion engine based on the in-cylinder pressure resonance phenomenon. Mechanical Systems and Signal Processing. 62-63:480-489. doi:10.1016/j.ymssp.2015.02.023. A direct transform for determining the trapped mass on an internal combustion engine based on the in-cylinder pressure resonance phenomenon AbstractIt has lately been demonstrated that the resonance of the in-cylinder pressure may be used for inferring the trapped mass in an internal combustion engine. The resonance frequency changes over time as the expansion stroke takes place, and hence time-frequency analysis techniques may be used for determining the instantaneous frequency. However, time-frequency analysis has different problems when obtaining the spectral content of the signal, e.g. Short-Time Fourier Transform dilutes the frequency spectrum, and the Wigner Distribution creates cross terms that difficult its interpretation. In addition, time-frequency analysis requires a significant computational burden. This paper presents a direct transform, based on the resonance phenomenon, which obtains the trapped mass by convolving the pressure trace with the theoretical resonance behaviour. The method permits avoiding the spectral problems of the time-frequency transformations by obtaining the trapped mass directly without the need of inferring the frequency content.

This paper presents a model for on-line NOx estimation. The method uses both, low frequency components and high frequency components of in-cylinder pressure signal: it harnesses in-cylinder pressure resonance to estimate the trapped mass, and based on this measurement, a NOx model is adapted to estimate NOx emissions cycle by cycle. In addition of the in-cylinder pressure signal, the procedure only requires from lambda and air mass flow to estimate NOx, so it can give a direct estimation of NOx or improve transient response and ageing of current NOx sensors. The method was validated on a CI engine with high pressure EGR loop under steady and transient conditions showing errors below 10 % and cycle by cycle time response.

In this paper, the knock phenomenon is studied and characterized by time-frequency analysis and a new definition that is capable of differentiating normal combustion from autoignition of the end gas, is proposed. The new definition permits detecting low-knocking cycles, and consequently, more knocking information is available for updating knock models or for improving knock control strategies. The new definition of knock is implemented online in a four stroke SI engine and its performance is illustrated by using a classical knock control strategy. Results obtained under different operating conditions demonstrate that the improved knock definition can substantially reduce the dispersion of Spark advance angle control and reach higher mean values, obtaining then, higher combustion efficiencies and reducing engine vibration.

New propulsive architectures, with high interactions with the aerodynamic performance of the platform, are an attractive option for reducing the power consumption, increasing the resilience, reducing the noise and improving the handling of fixed-wing unmanned air vehicles. Distributed electric propulsion with boundary layer ingestion over the wing introduces extra complexity to the design of these systems, and extensive simulation and experimental campaigns are needed to fully understand the flow behaviour around the aircraft. This work studies the effect of different combinations of propeller positions and angles of attack over the pressure coefficient and skin friction coefficient distributions over the wing of a 25 kg fixed-wing remotely piloted aircraft. To get more information about the main trends, a proper orthogonal decomposition of the coefficient distributions is performed, which may be even used to interpolate the results to non-simulated combinations, giving more information than an interpolation of the main aerodynamic coefficients such as the lift, drag or pitching moment coefficients.