Numerical investigations on hydrogen-enhanced combustion in ultra-lean gasoline spark-ignition engines

In-cylinder water injection is a promising approach for reducing NOx and soot emissions from internal combustion engines. It allows one to use a higher compression ratio by reducing engine knock; hence, higher fuel economy and power output can be achieved. However, water injection can also affect engine combustion and emission characteristics if water injection and injector parameters are not properly set. Majority of the previous studies on the water injection are done through experiments. Therefore, subtle aspects of water injection such as in-cylinder interaction of water sprays, spatial distribution of water vapor, and effect on flame propagation are not clearly understood and rarely reported in literature due to experimental limitations. Thus, in the present article, a computational fluid dynamics investigation is carried out to analyze the effects of direct water injection under various injector configurations on water evaporation, combustion, performance, and emission characteristics of a gasoline direct injection engine. The emphasis is given to analyze in-cylinder water spray interactions, flame propagation, water spray droplet size distribution, and water vapor spatial distribution inside the engine cylinder. For the study, the water-to-fuel ratio is varied from 0 to 1. Various water injector configurations using nozzle hole diameters of 0.14, 0.179, and 0.205 mm, along with nozzle holes of 4, 5, 6, and 7, are considered for comparison in addition to the case of no_water. Computational fluid dynamics models used in this study are validated with the available data in literature. From the results, it is found that the emission and performance characteristics of the engine are highly dependent on water evaporation characteristics. Also, the water-to-fuel ratio of 0.6 with 6 number of nozzle holes and the nozzle diameter of 0.14 mm results in the highest indicated mean effective pressure and the lowest NOx, soot, and CO emissions compared to other cases considered.

Section: Cfd Analysismentioning

confidence: 99%

Effects of direct water injection and injector configurations on performance and emission characteristics of a gasoline direct injection engine: A computational fluid dynamics analysis

Raut

Mallikarjuna

2019

“…The aero-thermochemical processes that take place in the cylinder are complex, and they have a deep influence on the engine efficiency, both in terms of performance and pollution. 1 To support research and development of new solutions and technologies, CFD has been increasingly adopted to address a wide variety of phenomena related to ICEs, such as heat transfer, 2–4 regular and abnormal combustion, 5–8 pollutant formation 9–11 and cycle-to-cycle variability (CCV). 12–14 Extensive research is still ongoing to improve the accuracy and the computational efficiency of CFD methods, such as numerical schemes, turbulence models, wall-functions, fuel spray models, combustion models and mesh motion techniques.…”

Section: Introductionmentioning

confidence: 99%

Large eddy simulation analysis of the turbulent flow in an optically accessible internal combustion engine using the overset mesh technique

Rulli

Barbato

Fontanesi

et al. 2020

Computational fluid dynamics has become a fundamental tool for the design and development of internal combustion engines. The meshing strategy plays a central role in the computational efficiency, in the management of the moving components of the engine and in the accuracy of results. The overset mesh approach, usually referred to also as chimera grid or composite grid, was rarely applied to the simulation of internal combustion engines, mainly because of the difficulty in adapting the technique to the specific complexities of internal combustion engine flows. The article demonstrates the feasibility and the effectiveness of the overset mesh technique application to internal combustion engines, thanks to a purposely designed meshing approach. In particular, the technique is used to analyze the cycle-to-cycle variability of internal combustion engine flows using large eddy simulation. Fifty large eddy simulation cycles are performed on the well-known TCC-III engine in motored condition. Results are analyzed in terms of tumble center trajectory and using proper orthogonal decomposition to objectively characterize the spatial and temporal evolution of turbulent flow field in internal combustion engines. In particular, an original decomposition method previously applied by the authors to the TCC-III measured flow fields is here extended to computational fluid dynamics results.

“…A Reynolds-averaged Navier–Stokes (RANS) combustion model based on the turbulent flame speed closure of Zimont et al, 26 Lipatnikov and Chomiak 27 and Zimont 28 was presented in Rakopoulos et al 29 for pure hydrogen and extended to consider admixtures by blending the used laminar flame speed correlations for the mono component fuels in Kosmadakis et al 30,31 A fixed hydrogen fraction in the fuel of 10 and 30 vol% was considered, for which good agreement with the experimental data was reported. More recently, a laminar flame speed correlation for lean gasoline–hydrogen admixtures in combination with the extended coherent flame model (ECFM) was proposed in Iafrate et al 32 and successfully validated against engine test bench data in order to highlight the positive effects of small hydrogen addition for different loads.…”

Section: Introductionmentioning

confidence: 99%

Reactive computational fluid dynamics modelling of methane–hydrogen admixtures in internal combustion engines: Part I – RANS

Koch

Schürch

Wright

et al. 2020

The effects of hydrogen addition to internal combustion engines operated by natural gas/methane has been widely demonstrated experimentally in the literature. Already small hydrogen contents in the fuel show promising benefits with respect to increased engine efficiency, lower CO2 emissions, extended lean operating limits and a higher exhaust gas recirculation tolerance while maintaining the knock resistance of methane. In this article, the influence of hydrogen addition to methane on a spark ignited single cylinder engine is investigated. This article proposes a modelling approach to consider hydrogen addition within three-dimensional reactive computational fluid dynamics in order to establish a framework to gain further insights into the involved processes. Experiments have been performed on a single-cylinder spark-ignition engine situated at a test bed and cater as reference data for validating the proposed reactive computational fluid dynamics modelling approach based around the G-Equation combustion model. Within the course of the first part, crucial aspects relevant to the modelling of the mean engine cycle are highlighted. In this article, a simplified early combustion phase model which considers the transition towards a fully developed turbulent flame following ignition is introduced, along with a second submodel considering combined effects of the walls. The sensitivity of the combustion process towards the modelling approach is presented. The submodels were calibrated for a reference operating point, and a sweep in hydrogen content in the fuel as well as stoichiometric and lean operation has been considered. It is shown that the flame speed coefficient A appearing in the used turbulent flame speed closure, weighting the influence of the turbulent fluctuating speed [Formula: see text], has to be adjusted for different hydrogen contents. The introduced submodels allowed for significant improvement of the in-cylinder pressure and heat release rate evolution throughout all considered operating conditions.