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The current numerical study aims to examine the single and combined effects of various piston bowl geometries, diesel main Start of Injection (SOI) timing, and syngas energy ratio on the combustion characteristics, specific emissions (g/kW·h), energy distribution, and exergy of a heavy-duty off-road Reactivity-Controlled Compression Ignition (RCCI) diesel engine. The examined geometries include the stock chamber (baseline combustion chamber), wide-shallow chamber, dual-swirl chamber, stepped-lip chamber. The main SOI timing was varied from −20 to −5 Crank Angle (CA) After Top Dead Center (ATDC) with 5 CA steps. Also, syngas energy ratio including 0% Conventional Diesel Combustion (CDC) mode, 20%, 40%, and 60% of total fuel energy per cycle. To accomplish this goal, the SAGE combustion model coupled with a reduced chemical kinetic mechanism consists of 360 reactions, and 72 species was applied to conduct this investigation. The numerical findings showed that the use of the wide-shallow chamber extended the engine operable range under diesel-syngas combustion operating conditions. In comparison to the baseline CDC case, the application of the dual-swirl chamber under CDC conditions, and main SOI timing of −15 CA ATDC led to reduction of Carbon Monoxide ([Formula: see text]), Hydro-Carbon ([Formula: see text]), Particle Matter ([Formula: see text]), Carbon Dioxide ([Formula: see text]), Indicated Specific Energy Consumption (ISEC), Gross Indicated Efficiency (GIE), and exergy efficiency but with a Nitrogen Oxides ([Formula: see text]) penalty rate. In general, an increase in the bore to bowl diameter ratio caused a shorter ignition delay period and combustion duration. The utilization of the stepped-lip chamber at both CDC and diesel-syngas combustion operating modes resulted in a shorter ignition delay period, but a longer combustion duration. Nonetheless, the stepped-lip combustion chamber reduced the diffusive flame temperature. Also, it is noteworthy that the utilization of the stock chamber along with the main SOI timing at −5 CA ATDC under diesel-syngas 60% combustion mode is a suitable technique to pass EURO-VI [Formula: see text] and [Formula: see text] emissions regulations.

This article presents a detailed analytical model to evaluate piston skirt tribology under hydrodynamic lubrication. The contribution of the piston ring pack lubrication has been taken into account to study piston secondary motion and tribological performance. A system of nonlinear equations comprising Reynolds equation and force equilibrium is solved to calculate piston ring pack friction force and its moment about wrist pin axis. Instantaneous minimum oil film thickness at piston ring/liner interface has been estimated considering different boundary conditions: full Sommerfeld, oil separation, and Reynolds cavitation and reformation. The ring pack model has capability to be used for a wide range of ring face profiles under boundary and hydrodynamic lubrication. Piston secondary motion is evaluated using lubrication theory and equilibrium of forces and moments, to examine the effect of wrist pin location, piston skirt/liner clearance, and oil rheology. Numerical method and finite difference scheme have been used to define piston eccentricity and hydrodynamic pressure acting over the skirt.