Experimental and CFD Investigation of Fuel Mixing in an Optical-Access Direct-Injection NG Engine and Correlation with Test Rig Combustion and Performance Data

Abstract

The present paper is the result of a cooperation between Politecnico di Torino and AVL List Gmbh within a recent collaborative research project funded by the EC. The research work was focused on the experimental and numerical characterization of mixture formation, combustion, and emissions in direct-injection NG engines, to draw useful indication for the design of innovative, high-performance engine concepts. As a matter of fact, direct-injection IC engines running on NG are believed to be a competitive transition solution towards a sustainable mobility scenario, given their maturity, technological readiness, and flexibility with respect to the fuel quality. Moreover, gaseous-fuel engines can further decrease their carbon footprint if blending of natural gas with hydrogen is considered. Provided that mixture formation represents a key aspect for the design of direct-injection engines, the activity presented in this paper is focused on the characterization of NG injection and on the mixing process, as well as the impact these latter hold on the combustion process as well as on engine-out emissions. The mixture formation process was analyzed by means of combined CFD and optical investigations. Furthermore, a full version of the engine was tested on a dynamic test rig, providing quantitative information on the engine performance and emission characteristics. The CFD results highlighted the correlation between the mixture homogeneity and the combustion stability and hinted at a relevant impact of the jet characteristics on the air charge tumble and turbulence characteristics.

High-Performance Hydrogen-Fueled Internal Combustion Engines: Feasibility Study and Optimization via 1D-CFD Modeling

“…The turbocharger was not included in the model in order to highlight the ideal requirements to the turbocharger device and avoid any limitation coming from it. In the second part, the conversion of a prototype high-performance engine, for which experimental data with NG fueling were available [10,25], was investigated by quantifying the effect of different turbomatching choices on the achievable performance and efficiency.…”

“…The second part of the investigation, which was kept within a 1D simulation framework, was devoted to the feasibility study of the conversion of an existing prototype engine to run on hydrogen. The engine design is the result of the cooperation of the authors' research group with Fiat Research Center, BorgWarner, AVL List GmbH within the GasOn research project [10,25] and features a direct injection concept, variable valve actuation and high structural integrity, which allowed a high CR to be adopted. A list of the main engine characteristics is reported in Table 2.…”

“…Second, the DI injection strategy was considered for the H 2 engine in order reduce the effect of the lower fuel density with respect to methane [24,25]. The EOI timing was set at −70 deg CA, which allows the volumetric efficiency to be maximized at low-end torque operating conditions, still keeping a reasonable time available for fuel-air mixing [10,25]. Figure 6 provides an example of comparison between the indicated cycles relative to the H 2 and the NG fueling for the same operating condition (3000 rpm and full load).…”

“…Second, the purity requirements are less stringent than in fuel cells, allowing for the exploitation of hydrogen coming as a side-product in many production processes [4]. Finally, hydrogen engines can benefit from the state of the art on dedicated, monofuel, NG engines [10,11], which have been developed to a great extent since the 1990s. An exhaustive review of advantages and drawbacks of the H 2 -ICE, as well as a thorough overview of the measures for the engine design or conversion, is provided in [4] and, more recently, in [12][13][14].…”

An Analysis of Mechanical and Thermal Stresses, Temperature and Displacement within the Transparent Cylinder and Piston Top of a Small Direct-Injection Spark-Ignition Optical Engine

“…Furthermore, Tornatore and Sjöberg [27] employed advanced optical diagnostic techniques, offering spatial and temporal precision, within a transparent engine configured to operate in the partial fuel stratification mode to stabilize overall lean combustion. In [28], the authors conducted experimental and numerical investigations to characterize mixture preparation, combustion and emissions in a direct-injection natural gas optical engine. Moreover, in [29], passively fueled pre-chamber spark plugs with varying geometries (three different types) were investigated in a single-cylinder direct-injection gasoline engine, utilizing high-speed in-cylinder imaging.…”