Search Results

Low pressure exhaust gases recirculation (LP-EGR) is becoming a state-of-the-art technique for Nitrogen oxides (NOx) reduction in compression ignited (CI) engines. However, despite the pollutant reduction benefits, LP-EGR suffers from strong non-linearities and delays which are difficult to handle, resulting in reduced engine performance under certain conditions. Measurement and observation of oxygen concentration at the intake have been a research topic over the past few years, and it may be critical for transition phases (from low pressure to high pressure EGR). Here, an adequate selection of models and sensors is essential to obtain a precise and fast measurement for control purposes. The present paper analyses different sensor configurations, with oxygen concentration measurements at the intake and exhaust manifold and combines observation techniques with sensor models to determine the potential of each configuration.

Dual-fuel combustion engines have shown the potential to extend the operating range of Homogeneous Charge Compression Ignition (HCCI) by using several combustion modes, e.g. Reactivity Controlled Compression Ignition (RCCI) at low/medium load, and Partially Premixed Compression (PPC) at high load. In order to optimize the combustion mode operation, the respective sensitivity to the control inputs must be addressed. To this end, in this work the extremum seeking algorithm has been investigated. By definition, this technique allows to detect the control input authority over the system by perturbing its value by a known periodic signal. By analyzing the system response and calculating its gradient, the control input can be adjusted to reach optimal operation. This method has been applied to a dual-fuel engine under fully, highly and partially premixed conditions where the feedback information was provided by in-cylinder pressure and NOx sensors.

The passive pre-chamber ignition concept has shown the potential of increasing the combustion efficiency at high load by allowing more advanced combustion phasing due to its rapid combustion. The optimization of the spark advance and the dilution rate is currently a challenging task that would allow these types of engines to maintain spark ignited (SI) engines pollutants with even higher combustion efficiencies than diesel engines. This paper is focused on the automatic calibration of a SI engine, when using the passive-chamber ignition concept. The sensitivity of the combustion efficiency to spark advance and dilution rate has been studied and an extremum seeking approach has been designed to optimize the control inputs by rejecting disturbances and maintaining certain limitations of cycle-to-cycle variability and misfires.

Knock is an abnormal phenomenon with in-cylinder pressure oscillations, which must be avoided to protect the engine from damage and to avoid excessive noise. Conventional control algorithms delay the combustion with the spark to avoid high knocking rates but reduce the thermal efficiency and restricts the performance of a spark ignition engine. The detection and characterization of low-knocking cycles might be used for improving knock control algorithms, however, it is a challenging task, as normal combustion also excite the different resonance modes and might be confused with knock. Most of the methods found in literature for knock detection use 0-Dimensional indicators, regardless of the angular evolution of the pressure oscillations. In this paper, the in-cylinder pressure oscillations evolution during the piston stroke is analyzed by using various time-frequency transformations.

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.