Effect of spark ignition location on the turbulent jet ignition characteristics in a lean burning natural gas engine

The Turbulent Jet Ignition is an effective concept to achieve stable lean burning for natural gas engines due to the multiple ignition sources, high ignition energy, and fast combustion rate. A variation of the ignition location has a non-negligible effect on the ignition performance of the TJI system. The present work aims to provide more details on this effect by numerical simulations. Both factors of the additional fuel supply to the pre-chamber and the in-cylinder flow field are taken into consideration in this study. A numerical model is built based on a lean burning natural gas engine and validated by experimental results. Five different spark ignition sources are equally arranged on the vertical axis of the pre-chamber, with different distances from the connecting orifices. Simulations are carried out under the same initial and boundary conditions except for the location of the ignition source. Combustion pressure, in-cylinder flow field, fuel mass fraction distribution, and heat release rate are analyzed to study the in-cylinder ignition and combustion process. The results show that a rotational flow and a non-uniform fuel distribution are formed in the pre-chamber during the compression stroke. The turbulent jet characteristics are significantly influenced by the coupling of two factors: the combustion rate inside the pre-chamber as well as the flame propagation distance from the ignition source to the connecting orifices. Rapid combustion rate and shorter flame propagation distance both lead to the earlier ejection of cold jets and hot jets. Among five ignition sources, the one located closest to the connecting orifices generates earlier hot jets with the highest mean velocity. The jets are more effective to ignite the lean mixture and could decrease the combustion duration of the main chamber.

Investigating the Origins of Cyclic Variability in Internal Combustion Engines Using Wall-Resolved Large Eddy Simulations

Modern internal combustion engines (ICE) operate at the ragged edge of stable operation characterized by high cycle-to-cycle variations (CCV). A key scientific challenge for ICE is the understanding, modeling, and control of CCV in engine performance, which can contribute to partial burns, misfire, and knock. The objective of the current study is to use high-fidelity numerical simulations to improve the understanding of the causes of CCV. Nek5000, a leading high-order spectral element, open source code, is used to simulate the turbulent flow in the engine combustion chamber. Multi-cycle, wall-resolved large-eddy simulations (LES) are performed for the General Motors (GM), Transparent Combustion Chamber (TCC-III) optical engine under motored operating conditions. The mean and root-mean-square (r.m.s.) of the in-cylinder flow fields at various piston positions are validated using PIV measurements during the intake and compression strokes. The large-scale flow structures, including the swirl and tumble flow patterns, are analyzed in detail and the causes for cyclic variabilities in these flow features are explained. The energy distribution across the different scales of the flow are quantified using one-dimensional energy spectra, and the effect of the tumble breakdown process on the energy distribution is examined. The insights from the current study can help us develop improved engine designs with reduced cyclic variabilities in the in-cylinder flow leading to enhanced engine performance.

Application of Conditional Space-Time Proper Orthogonal Decomposition to Engine In-Cylinder Flow Analysis

The cycle-to-cycle variation of engine in-cylinder flow is critical for the improvement of performance for spark-ignition internal combustion engines. Proper orthogonal decomposition (POD), with its ability to extract the most energetic fluctuation structure, is widely used to analyze the in-cylinder flow and understand the variation of its evolution in different cycles. However, both of the two existing approaches to use POD for engine flow analysis encounter difficulties when applied for this purpose. Phase-dependent POD decomposes a data set in which all samples are taken at a certain engine phase (crank angle) from different cycles, but the POD results at neighboring engine phases do not necessarily evolve coherently. Phase-invariant POD, when applied to analyze tumble flow, stretches/compresses and interpolates the flow fields obtained at different engine phases onto the same grid, and this deformation means that phase-invariant POD results are no longer significant in energy sense. To overcome these difficulties, we propose an adaptation of conditional space-time POD to work with engine flow, with which the flow within a range of engine phases in each cycle is considered as one sample. It is shown that the low-order modes obtained with conditional space-time POD capture fluctuation structures that evolve coherently, and these results are compared and contrasted with those of the two existing POD approaches. A reduced-order model of the engine in-cylinder flow is constructed based on the partial sum of the modes and coefficients obtained from the conditional space-time POD, and it is shown that this new reduced-order model identifies structure that is both coherent spatially and temporally.

Experiment and Investigation in Reducing Emission from an IC Engine by using Inlet Helical Roller

This research paper reports that in-cylinder flow formation in a combustion engine has a major influence on the combustion, emission and performance characteristics. Air and fuel enters the combustion chamber of an engine throughout the intake manifold with high velocity. So, it introduces a helical roller in the path of inlet stream of mixture. It achieved the swirl by using a component that could be easily integrated into any existing engines at low engine speed. The performance of the engine increases and completes the combustion, leads to reduced emissions and small change in volumetric efficiency. It is also proved that increased swirl movement introduces helical roller that helps the flame spread which used into constant heat transfer rate. This suggests to a new combustion technique that should be developed to yield improved primary combustion processes in-side the engine with significantly reduced exhaust gas emissions.

On the use of particle image velocimetry (PIV) data for the validation of Reynolds averaged Navier-Stokes (RANS) simulations during the intake process of a spark ignition direct injection (SIDI) engine

Computational fluid dynamics (CFD) simulations of the in-cylinder flow field are widely used in the design of internal combustion engines (ICEs) and must be validated against experimental measurements to enable a robust predictive capability. Such validation is complicated by the presence of both large-scale cycle-to-cycle variations and small-scale turbulent fluctuations in experimental measurements of in-cylinder flow fields. Reynolds averaged Navier-Stokes (RANS) simulations provide overall flow structures with acceptable accuracy and affordable computational cost for widespread industrial applications. Due to the nature of averaging physical parameters in RANS, its validation against experimental results obtained by particle image velocimetry (PIV) requires consideration of how best to average or filter the measured turbulent flows. In this paper, PIV measurements on the cross-tumble plane were recorded every five crank angle degrees for [Formula: see text] cycles during the intake process of a motored, optically accessible spark ignition direct injection (SIDI) engine. Several methods including ensemble averaging, speed-based averaging and low-order proper orthogonal decomposition (POD) reconstruction were applied to remove the fluctuations from experimental PIV vector fields and thus enable comparison to RANS simulations. Quantitative comparison metrics were used to evaluate the performances of each method in representing the intake jet. Recommendations are made on how to provide a fair validation between measured data and simulation results in highly fluctuating flow fields such as the engine intake jet.

The influence of in-cylinder flows and bulk gas density on early Spray G injection in an optical research engine

A well-characterized multi-hole gasoline injector, the Engine Combustion Network’s (ECN) Spray G injector, was investigated in an optically accessible research engine under four motored operating conditions with early injection. The experiments were conducted at intake pressures of [Formula: see text] and [Formula: see text], nearly matching the ECN’s standard early injection operating conditions, Spray G2 (flash boiling) and Spray G3 (early injection), respectively. This was combined with two engine speeds at [Formula: see text] and [Formula: see text]. Using particle image velocimetry and volumetric Mie scatter imaging, the in-cylinder flows were evaluated and the effects on the spray morphology were characterized. The in-cylinder flow was evaluated to understand the spray-flow interaction, including the turbulent kinetic energy. Little effect on turbulent energy was observed in the region examined near the exit of the fuel injector nozzle shortly after injection. Mie scatter imaging was used to characterize the spray morphology and wall wetting was clearly visible on the spark plug. Cyclic variability of the sprays was found to be insignificant; and major differences in spray morphology are attributed to the in-cylinder velocity and intake pressure at the time of injection. Decreasing the bulk gas density by decreasing the intake pressure had a number of effects on the evolution of the spray including faster evaporation, increased axial liquid penetration, and decreased spray angle. Increasing the in-cylinder flow magnitudes by increasing the engine speed had a similar effect on spray morphology by also increasing the evaporation rate, increasing the axial penetration, and decreasing the spray opening angle. Comparison of the motored spray cases with a no-flow case (when the fuel is sprayed into the engine without the piston present) further illustrated the extent to which the intake flow influenced the spray shape.