Numerical Analysis on the Potential of Different Variable Valve Actuation Strategies on a Light Duty Diesel Engine for Improving Exhaust System Warm Up

The need for achieving a fast warm up of the exhaust system has raised in the recent years a growing interest in the adoption of Variable Valve Actuation (VVA) technology for automotive diesel engines. As a matter of fact, different measures can be adopted through VVA to accelerate the warm up of the exhaust system, such as using hot internal Exhaust Gas Recirculation (iEGR) to heat the intake charge, especially at part load, or adopting early Exhaust Valve Opening (eEVO) timing during the expansion stroke, so to increase the exhaust gas temperature during blowdown.In this paper a simulation study is presented evaluating the impact of VVA on the exhaust temperature of a modern light duty 4-cylinder diesel engine, 1.6 liters, equipped with a Variable Geometry Turbine (VGT). Numerical simulations were carried out by means of a commercially available 1D-CFD software (GT-SUITE) and a predictive combustion model (DIPulse) was adopted in order to properly evaluate the impact of different VVA strategies on the combustion process. The analysis was focused on the assessment of the potential of 3 different VVA strategies for managing the exhaust temperature: Early Exhaust Valve Opening (EEVO), obtained by means of valve lift modifications, Exhaust Phasing, by changing the valve timing, and Exhaust Valve ReOpening (EVrO) during the intake stroke for iEGR. Moreover, for the EVrO strategy, two different EGR combinations (iEGR-only and low pressure EGR with iEGR, respectively) were evaluated to identify the best trade-off between the exhaust temperature increase and the Brake Specific Fuel Consumption (BSFC) penalty.Thanks to the abovementioned VVA strategies, in steady state conditions increases in the exhaust temperature up to 70 K with BSFC penalties below 8% at low engine loads were achieved. Finally, the impact of VVA strategies was evaluated under transient conditions over the WLTC (Worldwide harmonized Light vehicles Test Cycle), highlighting a temperature increase of 30 K of the Diesel Oxidation Catalyst after the first 300 s with a total fuel consumption penalty lower than 1%.

[1]  Qianfan Xin,et al.  Diesel engine system dynamics, transient performance, and electronic controls , 2011 .

[2]  Bernardo Sousa Ribeiro,et al.  Direct Comparison of an Engine Working under Otto, Miller and Diesel Cycles: Thermodynamic Analysis and Real Engine Performance , 2007 .

[3]  Jesús Benajes,et al.  Intake Valve Pre-lift Effect on the Performance of a Turbocharged Diesel Engine , 1996 .

[4]  Yaodong Wang,et al.  Experimental investigation of applying miller cycle to reduce NOx emission from diesel engine , 2005 .

[5]  Mahsa Rafigh.  Exhaust aftertreatment modeling for efficient calibration in diesel passenger car applications , 2017 .

[7]  F. Millo,et al.  Impact of high sulfur fuel and de-sulfation process on a close-coupled diesel oxidation catalyst and diesel particulate filter , 2017 .

[8]  Rosli Abu Bakar,et al.  Investigation of Diesel Engine Performance Based on Simulation , 2008 .

[9]  Federico Millo,et al.  Optimizing the Calibration of a Turbocharged GDI Engine through Numerical Simulation and Direct Optimization , 2010 .

[10]  Peter L. Mtui,et al.  Performance And Emissions Modeling Of Natural Gas Dual Fuelling Of Large Diesel Engines , 2013 .

[11]  Martti Larmi,et al.  NOx Reduction in a Medium-Speed Single-Cylinder Diesel Engine using Miller Cycle with Very Advanced Valve Timing , 2009 .

[12]  G. B. Parvate-Patil,et al.  Analysis of Variable Valve Timing Events and Their Effects on Single Cylinder Diesel Engine , 2004 .

[13]  Federico Millo,et al.  Analysis of Different Internal EGR Solutions for Small Diesel Engines , 2007 .

[14]  Federico Millo,et al.  Assessment of the Predictive Capabilities of a Combustion Model for a Modern Common Rail Automotive Diesel Engine , 2016 .

[15]  F. Millo,et al.  The Potential of Dual Stage Turbocharging and Miller Cycle for HD Diesel Engines , 2005 .

[16]  Shengqiang Huang,et al.  Internal EGR Systems for NOx Emission Reduction in Heavy-Duty Diesel Engines , 2004 .