Control-oriented modeling of two-stroke diesel engines with exhaust gas recirculation for marine applications

Abstract

Large marine two-stroke diesel engines are widely used as propulsion systems for shipping worldwide and are facing stricter N O x emission limits. Exhaust gas recirculation (EGR) is introduced to these engines to reduce the produced combustion N O x to the allowed levels. Since the current number of engines built with EGR is low and engine testing is very expensive, a powerful alternative for developing EGR controllers for such engines is to use control-oriented simulation models. Unfortunately, the same reasons that motivate the use of simulation models also hinder the capacity to obtain sufficient measurement data at different operating points for developing the models. A Mean Value Engine Model (MVEM) of a large two-stroke diesel with EGR that can be simulated faster than real time is presented and validated. An analytic model for the cylinder pressure that captures the effects of changes in the fuel control inputs is also developed and validated with cylinder pressure measurements. A parameterization procedure that deals with the low number of measurement data available is proposed. After the parameterization, the model is shown to capture the stationary operation of the real engine well. The transient prediction capability of the model is also considered satisfactory which is important if the model is to be used for EGR controller development during transients. Furthermore, the experience gathered while developing the model about essential signals to be measured is summarized, which can be very helpful for future applications of the model. Finally, models for the ship propeller and resistance are also investigated, showing good agreement with the measured ship sailing signals during maneuvers. These models give a complete vessel model and make it possible to simulate various maneuvering scenarios, giving different loading profiles that can be used to investigate the performance of EGR and other controllers during transients.

Modeling and Control of EGR on Marine Two-Stroke Diesel Engines

“…A computationally faster approach is taken in Sui et al [42], using a Seiliger cycle to model the in-cylinder pressure of a medium speed marine diesel engine. Paper 5 [43] of the thesis contributes with an algebraic in-cylinder pressure model that captures the effects of the ordered exhaust valve and fuel injection angles on the cylinder pressure. Cylinder pressure measurements are used to validate the proposed analytic model based on an adaptation of the work described in Eriksson and Andersson [44], from automotive four-stroke engines to marine two-stroke applications.…”

“…Algebraic models are well suited for control application models since they have low computational requirements. Hence, the original model from Andersen [50] is used in Paper 5 [43] of the thesis, but the model is adapted to a larger engine than the one studied in the original publication.…”

“…The compressor model is described in Papers 1 and 2 [81,82]. A more detailed MVEM is introduced in Paper 5 [43], where the generality of the model approach is shown by modeling another engine with EGR. The MVEM from Paper 5 proposes improvements on several components and includes models for the propeller and the ship surge dynamics to have a complete ship propulsion model.…”

“…For the case of Paper 5 [43], the data sources are the continuous recordings of the installed sensors on the ship engine during normal sailing operation. Figure 2.6 shows an example of several measured signals from the sailing vessel with an identified stationary point highlighted.…”

“…Hence, the stationary parameterization of the marine engine model has to be done at once, which increases its complexity substantially. In Paper 5 [43] of this thesis, a different approach to obtain an estimate of the air mass flow when EGR is disabled is described, using the compressor model from Papers 1 and 2 [81,82]. This method simplifies the parameterization process but requires measurements of turbocharger speed, compressor inlet temperature and pressure, and compressor outlet pressure.…”