Air Flow Optimization and Calibration in High-Compression-Ratio Naturally Aspirated SI Engines with Cooled-EGR

Abstract

As part of the U.S. Environmental Protection Agency (U.S. EPA) "Midterm Evaluation of Light-duty Vehicle Standards for Model Years 2022-2025 [1]", the U.S. EPA is evaluating engines and assessing the effectiveness of future engine technologies for reducing CO2 emissions. Such assessments often require significant development time and resources in order to optimize intake and exhaust cam variable valve timing (VVT), exhaust gas recirculation (EGR) flow rates, and compression ratio (CR) changes. Mazda SkyActiv-G spark-ignition (SI) engines were selected by EPA for an internal engine development program based upon their high geometric compression ratio (14:1 in Europe and Japan, 13:1 in North America) and their use of a flexible valve train configuration with electro-mechanical phasing control on the intake camshaft. A one-dimensional GT-Power engine model was calibrated and validated using detailed engine dynamometer test data [2] from 2.0L and 2.5L versions of the SkyActiv-G engine. The calibrated GTPower model and a Mathworks Model-Based Calibration (MBC) tool box are being used by EPA to explore calibration and control development of intake and exhaust cam phasing, and cooled EGR flow rates to reduce CO2 and improve brake thermal efficiency. This paper presents initial results of a parametric study to determine appropriate rates of cooled, external EGR (cEGR); internal (residual) EGR; and control development for a future engine technology demonstration project based upon the 2.0L, 14:1 CR version of the Mazda SkyActiv-G engine. An optimization routine was used to determine a combination of intake and exhaust cam timing, light-load internal EGR, and cEGR flow rates while satisfying the constraints of engine knock, brake torque and other functional requirements. The engine model was found to be useful for rapid engine calibration development. The modeling tools developed in this work were also used to conduct an initial evaluation of the CO2 reduction potential of a 1-point change in geometric CR, cEGR, and application of cylinder de-activation. Upon further development, the resulting fuel flow maps can subsequently serve as inputs into EPA's ALPHA [3, 4] vehicle energy model simulations.

Optimization of a Spark Ignition Engine Knock and Performance Using the Epsilon-Constrained Differential Evolution Algorithm and Multi-Objective Differential Evolution Algorithm

“… where M 1 is the induction time multiplier, a i through f i are the constant parameters of the model, ON represents the octane number of the fuel used to run the engine, [Diluent] means the mass fraction of the residuals in the unburned zone, mainly including N 2 , CO 2 , and H 2 O, and M 2 is the activation energy multiplier. 30 …”

“…In order to capture the different chemistry of knock lover a wide range of temperatures, the kinetics-fit model uses three different induction times to describe the knock in the low-, intermediate-, and high-temperature regions, respectively. , The overall induction time of this model comprises three different induction times. − Each induction time is defined by eq . where M 1 is the induction time multiplier, a i through f i are the constant parameters of the model, ON represents the octane number of the fuel used to run the engine, [Diluent] means the mass fraction of the residuals in the unburned zone, mainly including N 2 , CO 2 , and H 2 O, and M 2 is the activation energy multiplier …”

“…47−49 Each induction time is defined by eq 5. where M 1 is the induction time multiplier, a i through f i are the constant parameters of the model, ON represents the octane number of the fuel used to run the engine, [Diluent] means the mass fraction of the residuals in the unburned zone, mainly including N 2 , CO 2 , and H 2 O, and M 2 is the activation energy multiplier. 30 The overall induction time integral is defined by eq 6. When the overall induction time is integrated to 1, the knock occurs at t knock .…”

Modeling the Effects of Transmission Gear Count, Ratio Progression, and Final Drive Ratio on Fuel Economy and Performance Using ALPHA

“…• A 2010-era engine with dual cam phasing (DCP) [14,15] • The 2013 Chevy Malibu engine as used in previous modeling efforts [12] • The 2014 Mazda Skyactiv 2L, 13:1 compression ratio (CR) [16] • A hypothetical "2020" downsized boosted engine, 24 bar, with cooled EGR [14,15] The engines represent a range of past, current, and future technologies. Three of the engines are naturally aspirated and the fourth represents a hypothetical future downsized boosted engine.…”

Potential Fuel Economy Improvements from the Implementation of cEGR and CDA on an Atkinson Cycle Engine

“…Two of the future technologies assessed in the 2012 rulemaking were cEGR and CDA. In earlier work published by EPA, 1-D gas dynamics and 0-D combustion modeling was conducted using a Gamma Technologies GT-POWER™ model of an Atkinson cycle engine with these technologies [2]. In this investigation, a base Atkinson engine map was obtained from dynamometer testing of a U.S. certified 2.0L 13:1 CR Mazda SkyActiv engine.…”