Search Results

To understand key practical aspects of ammonia as a fuel for internal combustion engines, three-dimensional computational fluid dynamics (CFD) simulations were performed using CONVERGETM. A light-duty single-cylinder research engine with a geometrical compression ratio of 11.5 and a conventional pentroof combustion chamber was experimentally operated at stoichiometry. The fumigated ammonia was introduced at the intake plenum. Upon model validation, additional sensitivity analysis was performed. The combustion was modeled using a detailed chemistry solver (SAGE), and the ammonia oxidation was computed from a 38-specie and 262-reaction chemical reaction mechanism. Three different piston shapes were assessed, and it was found that the near-spark flow field associated with the piston design in combination with the tumble motion promotes faster combustion and yields enhanced engine performance.

The pre-chamber combustion can extend the lean limit of internal combustion engines (ICE) and hence increase their overall efficiency. Compared to active pre-chambers equipped with an auxiliary fuel supply system, passive pre-chambers have lower manufacturing costs and require minimal or no design modifications to the conventional spark plug engines. The major challenge of the passive pre-chamber is to extend the lean limit as much as the active pre-chamber. Computational fluid dynamics (CFD) simulations were conducted on a light-duty single-cylinder engine geometry fitted with a passive pre-chamber and using iso-octane as fuel to investigate and optimize the passive pre-chamber fuel enrichment through the pre-chamber nozzles. The non-reacting flow simulations were performed from the intake valve open (IVO) to spark timing.

To elucidate the complex characteristics of pre-chamber combustion engines, the interaction of the hot gas jets initiated by an active narrow throated pre-chamber with lean premixed CH4/air in a heavy-duty engine was studied computationally. A twelve-hole KAUST proprietary pre-chamber geometry was investigated using CONVERGE software. The KAUST pre-chamber has an upper conical part with the spark plug, and fuel injector, followed by a straight narrow region called the throat and nozzles connecting the chambers. The simulations were run for an entire cycle, starting at the previous cycle's exhaust valve opening (EVO). The SAGE combustion model was used with the chemistry modeled using a reduced methane oxidation mechanism based on GRI Mech 3.0, which was validated against in-house OH chemiluminescence data from the optical engine experiments.

Pre-chamber combustion (PCC) engines allow extending the lean limit of operation compared to common SI engines, thus being a candidate concept for the future clean transportation targets. To understand the fundamental mechanisms of the main chamber charge ignition in PCC engines, the effects of the composition in the pre-chamber were investigated numerically. A well-stirred reactor combustion model coupled with a methane oxidation mechanism reduced from GRI 3.0 was used. An open-cycle simulation was run with initialization at exhaust valve opening (EVO). For posterior simulations, the initial flow field was attained by mapping the field variables obtained from the full cycle simulation. The entire simulation domain (pre-chamber and main chamber) global excess air ratio (λ) was set to 1.3.

Towards a fundamental understanding of the ignition characteristics of pre-chamber (PC) combustion engines, computational fluid dynamics (CFD) simulations were conducted using CONVERGE. To assist the initial design of the KAUST pre-chamber engine experiments, the primary focus of the present study was to assess the impact of design parameters such as throat diameter, nozzle diameter, and nozzle length. The well-stirred reactor combustion model coupled with a methane oxidation mechanism reduced from GRI 3.0 was used. A homogeneous charge of methane and air with λ = 1.3 on both the PC and main chamber (MC) was assumed. The geometrical parameters were shown to affect the pre-chamber combustion characteristics, such as pressure build-up, radical formation, and heat release as well as the composition of the jets penetrating and igniting the main chamber charge. In addition, the backflow of species pushed inside the pre-chamber due to the flow reversal (FR) event was analyzed.

To provide insights into the fundamental characteristics of pre-chamber combustion engines, the ignition of lean premixed CH4/air due to hot gas jets initiated by a passive narrow throated pre-chamber in a heavy-duty engine was studied computationally. A twelve-hole pre-chamber geometry was investigated using CONVERGETM software. The numerical model was validated against the experimental results. To elucidate the main-chamber ignition mechanism, the spark plug location and spark timing were varied, resulting in different pressure gradient during turbulent jet formation. Different ignition mechanisms were observed for turbulent jet ignition of lean premixed CH4/air, based on the geometry effect. Ignition behavior was classified into the flame and jet ignition depending on the significant presence of hot active radicals. The jet ignition, mainly due to hot product gases was found to be advanced by the addition of a small concentration of radicals.