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Modeling the effect of variable cam phasing on volumetric efficiency, scavenging and torque generation in SI engines
KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.ORCID iD: 0000-0002-3672-5316
KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
(English)In: Control Engineering Practice, ISSN 0967-0661Article in journal (Other academic) Submitted
Abstract [en]

In a mean value engine model, the mass flow of air through thecylinders is determined by the air density, the engine speed, and thevolumetric efficiency. For modern engines the volumetric efficiency model mustalso account for the effect of variable valve timings. In this work the effect of the valve overlap is considered. Thevalve overlap is the number of crank angle degrees that both valvesare open simultaneously. When the valve overlap is significant,there may be fresh air that flows directly through the exhaustvalve, known as scavenging, which affects the torque. Steady-state torque measurements are used to estimate the amount of scavenging. The volumetric efficiency and scavenging models derived in the paper are shown toimprove the predictions of the engine torque significantly, alsounder transient conditions.

National Category
Control Engineering
URN: urn:nbn:se:kth:diva-102842OAI: diva2:557054

QS 2012

Available from: 2012-09-26 Created: 2012-09-26 Last updated: 2012-09-28Bibliographically approved
In thesis
1. Modeling, Control and Optimization of theTransient Torque Response in DownsizedTurbocharged Spark Ignited Engines
Open this publication in new window or tab >>Modeling, Control and Optimization of theTransient Torque Response in DownsizedTurbocharged Spark Ignited Engines
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Increasing demands for lower carbon dioxide emissions and fuel consumption drive technological developments for car manufacturers. One trend that has shown success for reducing fuel consumption in spark ignited engines is downsizing, where the engine size is reduced to save fuel and a turbocharger is added to maintain the power output. A drawback of this concept is the slower torque response of a turbocharged engine. Recent hardware improvements have facilitated the use of variable geometry turbochargers (VGT) for spark ignited engines, which can improve the transient torque response. This thesis addresses the transient torque response through three papers.

Paper 1 presents the optimal control of the valve timing and VGT for a fast torque response. Optimal open-loop control signals are found by maximizing the torque integral for a 1-d simulation model. From the optimization it is found that keeping the ratio between exhaust and intake pressure at a constant level gives a fast torque response. This can be achieved by feedback control using vgt actuation. The optimal valve timing differs very little from a fuel consumption optimal control that uses large overlap. Evaluation on an engine test bench shows improved torque response over the whole low engine speed range.

In Paper 2, model based, nonlinear feedback controllers for the exhaust pressure are presented. First, the dynamic relation between requested VGT position and exhaust pressure is modeled. This model contains an estimation of the on-engine turbine flow map. Using this model, a controller based on inverting the input-output relation is designed. Simulations and measurements on the engine show that the controller handles the strong nonlinear characteristic of the system, maintaining both stability and performance over the engine’s operating range.

Paper 3 considers the dependence of the valve timing for the cylinder gas exchange process and presents a torque model. A data-based modeling approach is used to find regressors, based on valve timing and pressures, that can describe the volumetric efficiency for several engine speeds. Utilizing both 1-d simulations and measurements, a model describing scavenging is found. These two models combine to give an accurate estimation of the in-cylinder lambda, which is shown to improve the torque estimation. The models are validated on torque transients, showing good agreement with the measurements.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xi, 61 p.
Trita-EE, ISSN 1653-5146 ; 2012:031
Engine modeling, Engine control, Transient torque response, Downsizing, Transient optimization
National Category
Control Engineering
urn:nbn:se:kth:diva-102743 (URN)978-91-7501-441-8 (ISBN)
Public defence
2012-10-19, F3, Lindstedsvägen 26, KTH, Stockholm, 13:15 (English)
TrenOp, Transport Research Environment with Novel Perspectives

QC 20120928

Available from: 2012-09-28 Created: 2012-09-24 Last updated: 2013-04-10Bibliographically approved

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Mårtensson, JonasFlärdh, Oscar
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