Experimental and modeling analysis on the optimization of combined VVT and EGR strategies in turbocharged direct-injection gasoline engines with VNT

Abstract

The combination of a growing number of complex technologies in internal combustion engines (ICE) is commonplace, due to the need of complying with the tight pollutant regulations and achieving high efficiencies. Hence the work of calibration engineers is led by a constant increase in degrees of freedom in ICE design. In this research work, a wide analysis on the optimization of combined variable valve timing (VVT) and exhaust gases recirculation (EGR) strategies is developed, in order to reduce fuel consumption in a EURO 6 1.3l 4-stroke 4-cylinder, gasoline, turbocharged, direct-injection engine, also equipped with a variable nozzle turbine (VNT). For that purpose, a methodology which combines 1D engine simulations with limited experimental work was applied. First, the data from 25 experimental tests distributed into three steady engine operating conditions was used to calibrate a 1D model. Then, modeling parametric studies were performed to optimize VVT and EGR parameters. A total of 150 cases were simulated for each operating point, in which VVT settings and EGR rate were varied at iso-air mass flow and iso-intake manifold temperature. The optimization was based on finding the configuration of VVT and EGR systems which maximizes the indicated efficiency. All different cases modeled were also evaluated in terms of pumping and heat losses. Moreover, a deep assessment of instantaneous pressure traces and mass flows in intake and exhaust valves was given, to provide insights about the optimization procedure. Finally, the findings obtained by simulation were compared with the results from a design of experiments (DOE) composed of more than 300 tests, and the impact on engine fuel consumption was analyzed.

Compressor Surge Mitigation in Turbocharged Spark-Ignition Engines without an Anti-Surge Control System during Load-Decrease Operation

“…As mentioned above, the installation of the intake flap is required to increase EGR rate and, consequently, fuel efficiency. Indeed, notable improvements in fuel consumption were achieved with high EGR operation in the same engine, as shown in a previous study [33]. In pursuit of simplicity, however, no EGR was used in the tests to reduce the degrees of freedom.…”

Assessment of air-management strategies to improve the transient performance of a gasoline engine under high EGR conditions during load-decrease operation

“…To this end, diverse tip-outs at 1500 rpm from 6 to 0.7 bar BMEP have been tested and modeled. Moreover, it should be remarked that the optimum EGR rate is 28% at the starting point, as reported in Galindo et al, 34 and 0% at the ending point. The impact of combined valve synchronization and SAP strategies on the engine transient operation were evaluated with both experimental and modeling data, while the addition of fresh air through the PAT system was separately assessed only by simulation.…”

“…33 In addition, it should be noted that the same engine model was already utilized for a previous research work, in which the interaction between EGR and VVT strategies in GTDI engines was widely analyzed, mainly from the air management perspective, under steady-state operating conditions. 34 The pressurized air tank (PAT) and SAP systems were also appended to the engine 1D model. Figure 2 shows a diagram of the intake manifold, SAP and PAT sub-models.…”

Identification and analysis of the factors to realizing variable intake/exhaust phases in opposed-piston two-stroke diesel engines

“…The VVT can effectively improve thermal efficiency and reduce emissions of the conventional engine. 10,11 The VVT technology has been widely used in traditional four-stroke engines. 12,13 However, the VVT technology has not yet been applied to OP2S diesel engines.…”