Air Flow Optimization and Calibration in High-Compression-Ratio Naturally Aspirated SI Engines with Cooled-EGR
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
Benchmarking a 2018 Toyota Camry 2.5-liter Atkinson Cycle Engine with Cooled-EGR.
As part of the U.S. Environmental Protection Agency's (EPA's) continuing assessment of advanced light-duty automotive technologies in support of regulatory and compliance programs, a 2018 Toyota Camry A25A-FKS 4-cylinder, 2.5-liter, naturally aspirated, Atkinson Cycle engine with cooled exhaust gas recirculation (cEGR) was benchmarked. The engine was tested on an engine dynamometer with and without its 8-speed automatic transmission, and with the engine wiring harness tethered to a complete vehicle parked outside of the test cell. Engine and transmission torque, fuel flow, key engine temperatures and pressures, onboard diagnostics (OBD) data, and Controller Area Network (CAN) bus data were recorded. This paper documents the test results under idle, low, medium, and high load engine operation. Motoring torque, wide open throttle (WOT) torque and fuel consumption are measured during transient operation using both EPA Tier 2 and Tier 3 test fuels. The design and performance of this 2018 2.5-liter engine is described and compared to Toyota's published data and to EPA's previous projections of the efficiency of an Atkinson Cycle engine with cEGR. The Brake Thermal Efficiency (BTE) map for the Toyota A25A-FKS engine shows a peak efficiency near 40 percent, which is the highest value of any publicly available map for a non-hybrid production gasoline internal combustion (IC) engine designed to run on 91 RON fuel. Further improvement is possible by application of fixed discrete or full continuous cylinder deactivation, both of which are currently in production on other engines.
Measurement and Analysis of the Residual Gas Fraction in an SI Engine with Variable Cam Timing
A spontaneous Raman scattering diagnostic was used to measure the residual fraction in a single-cylinder, 4-valve optically accessible engine. The engine was operated at 1500 rpm on pre-vaporized iso-octane at several intake manifold pressures (50-90 kPa). Cam phasing was varied to determine the effect of intake valve timing and valve overlap on the residual mass fraction of the engine. A simple model based on the ideal Otto cycle and 1D gas flow through the exhaust valves was proposed to analyze the results of the Raman experiment. The model showed good agreement (R 2 =0.91) with the experimental results and demonstrated its potential for use as a method to estimate the residual fraction in an engine from available dynamometer data. The experimental results showed that the residual fraction was reduced at higher manifold pressures due to less backflow through the exhaust valves and varied with intake cam phasing. The variation with intake cam phasing was determined by the gas properties in the cylinder when the intake valve opened. When the engine was stable (Coefficient of Variance (CoV) imep < 3%), changing the manifold pressure did not affect the portion of the residual fraction due to mass trapped at intake valve opening (IVO) and influenced the residual levels by reducing the residual level due to backflow.