Influence of droplet clustering in sprays on liquid deposition rate on spherical targets

[EN] The origin of temporal fluctuations of liquid mass deposition rates, obtained from a spray of droplets impinging on a solid spherical target, was investigated by correlation with droplet clusters in the spray. The droplet clusters were quantified using a Voronoi analysis on instantaneous images of the droplets, to obtain the number of droplet clusters, the area of the clusters and the number of droplets in each cluster. It was found that the normalised area of the droplet clusters had a distribution with a peak around 10-1 and a right tail which followed a power law of exponent -1.8. As the number density of the droplets inside the clusters increased, the temporal fluctuations of the liquid mass deposition rates increased, as a greater variation of droplet sizes impinged the target. However, as the standard deviation of the distribution of the normalised droplet cluster areas was increased, the temporal fluctuations in the liquid mass deposition rates reduced, as variations to the droplet number density and droplet sizes inside the clusters were averaged out.We would like to acknowledge financial support from Procter and Gamble through an EPSRC industrial case studentship and EPSRC grant EP/K019732/1.Andrade, P.; Charalampous, G.; Hardalupas, Y. (2017). Influence of droplet clustering in sprays on liquid deposition rate on spherical targets. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 513-520. https://doi.org/10.4995/ILASS2017.2017.4673OCS51352

Multiscale laminar flows with turbulentlike properties.

Accepted versio

Chemical species tomographic imaging of the vapour fuel distribution in a compression-ignition engine

This article reports the first application of chemical species tomography to visualise the in-cylinder fuel vapour concentration distribution during the mixing process in a compression-ignition engine. The engine was operated in motored conditions using nitrogen aspiration and fired conditions using a gasoline-like blend of 50% iso-dodecane and 50% n-dodecane. The tomography system comprises 31 laser beams arranged in a co-planar grid located below the injector. A novel, robust data referencing scheme was employed to condition the acquired data for image reconstruction using the iterative Landweber algorithm. Tomographic images were acquired during the compression stroke at a rate of 13 frames per crank angle degree within the same engine cycle at 1200 r min−1. The temperature-dependent fuel evaporation rate and mixing evolution were observed at different injection timings and intake pressure and temperature conditions. An initial cross-validation of the tomographic images was performed with planar laser-induced fluorescence images, showing good agreement in feature localisation and identification. This is the first time chemical species tomography using near-infrared spectroscopic absorption has been validated under engine conditions, and the first application of chemical species tomography to a compression-ignition engine

A computational study of the use of hydrogen peroxide as pilot fuel for a homogeneous mixture of ammonia/hydrogen in a compression ignition engine

We report a computational investigation of a compression ignition (CI) engine (compression ratio: 17.6, displacement volume: 1.3 L) where the main fuel is a homogeneous mixture of ammonia (70-60% vol%) and hydrogen (30-40% vol%), with a global equivalence ratio varying between 0.44 and 0.5, depending on the H2/NH3 ratio. The novelty of this study is that it employs a pilot injection of hydrogen peroxide to initiate ignition, without the use of any air or charge preheating (the temperature/pressure at intake BDC are 330 K/1.4 atm, representing mild boost an defficeint intervooling). Hydrogen peroxide (H2O2) has the attributes that it can be produced from renewable sources, and it is already widely manufactured, distributed, and stored, with diverse applications (as an aqueous solution of H2O2 with shares up to 30 vol%). The main advantage of using H2O2 as pilot fuel, as opposed to other more conventional ones (e.g., diesel), is that it contains no carbon, and hence produces no CO2 and particulate matter (PM). The computational investigation was conducted with an advanced commercial stochastic engine model that has been previously validated. The investigation was primarily focused on assessing the effects of using hydrogen peroxide in aqueous solution as pilot fuel on engine efficiency, combustion phasing and NOx emissions. These three aspects were investigated over a range of engine speeds (750-1,750 rpm) in view of: (i) the variation of the mass of the directly injected (DI) aqueous solution (0.1-10 mg); (ii) the variation of the H2O2 share (15-50%) in the directly injected (DI) aqueous solution; (iii) the variation of the start of injection (from -20 to -4 CAD aTDC) and injection duration (1-8 CAD). There is a strong effect of the peroxide in advancing combustion timing (CAD50 is advanced by up to 15 CAD) and in decreasing combustion duration (CAD90-CAD10 decreases up to 10 CAD), and peroxide readily enables medium engine loads which are the ones investigated in this work. Indicated thermal efficiencies above 50% were readily achieved at all engine speeds and, with a 30 vol% peroxide share in the solution, the pressure rise rate was always below 30 bar/ms. However, the NOx emissions in all cases exceeded the IMO’s Tier III standard. Possible ways to tackle this would be either the use of exhaust gas recirculation, or optimisation of the injection strategy, or the use of aftertreatment. For most cases, on a volume basis, the required aqueous H2O2 amount is 3% of the main fuel while on an energy basis this translates to 1.1% of the main fuel blend. The results reported in this initial study are promising because it is possible to ignite a premixed charge on the basis of a small pilot volume of commercially available hydrogen peroxide solutions

Engine performance and emissions from a fumigated hydrogen/ammonia compression ignition engine with a hydrogen peroxide pilot

The study investigates, numerically, the potential use of introducing aqueous HO as an ignition promoter in a statistically homogeneous NH/H fuelled, medium speed (1250 rpm), 4-stroke, 1.3 litre cylinder displacement, mildly boosted CI engine with a compression ratio of 17.6:1. The H is considered to be produced on-board from ammonia cracking. An extensive campaign is undertaken using the commercial stochastic reactor model, SRM Engine Suite, which allowed the modelling of temporal, temperature and spatial stratification in the cylinder. The engine performance, combustion phasing, maximum pressure rise rate and emissions (NOx, NO and unreacted NH) are investigated in view of: (i) the share of molecular hydrogen in the initial NH/H mixture from 10 to 40 percent; (ii) the mass of aqueous HO introduced from 0.1 to 16 mg; (iii) the start of injection (−10 to ＋6 CAD aTDC) and duration of injection (1, 4 and 8 CAD); (iv) the amount of exhaust gas recirculation (up to 30 percent by mass); (v) the share of energy from the HO in the aqueous solution mixture at less than 0.5 percent of that in the main fuel; (vi) engine load corresponding to a variation in the equivalence ratio from 0.32 to 1.2 by changing the mass of the NH/H mixture in the combustion chamber. A wide range of loads (evaluated against the engine’s rated power when operated with diesel and at its rated boost levels) can be achieved (44%–93%) with the energy share of HO being as little as equivalent to 2.7% vol% that of the main fuel, ammonia, which is introduced into the cylinder. This implies that the required storage volume of the HO is low, at a few percent that of the main ammonia tank. NOx emissions peak between .6−0.65 and rapidly decrease as the equivalence ratio increases or decreases reaching values marginally above the Tier III standard at high loads (90%) while ammonia slip and NO emissions are generally extremely low (10−12 mg for NH and 0.01 mg/kWh for NO)

A computational study of the use of hydrogen peroxide as pilot fuel for a homogeneous mixture of ammonia/hydrogen in a compression ignition engine

We report a computational investigation of a compression ignition (CI) engine (compression ratio: 17.6, displacement volume: 1.3 L) where the main fuel is a homogeneous mixture of ammonia (70-60% vol%) and hydrogen (30-40% vol%), with a global equivalence ratio varying between 0.44 and 0.5, depending on the H2/NH3 ratio. The novelty of this study is that it employs a pilot injection of hydrogen peroxide to initiate ignition, without the use of any air or charge preheating (the temperature/pressure at intake BDC are 330 K/1.4 atm, representing mild boost an defficeint intervooling). Hydrogen peroxide (H2O2) has the attributes that it can be produced from renewable sources, and it is already widely manufactured, distributed, and stored, with diverse applications (as an aqueous solution of H2O2 with shares up to 30 vol%). The main advantage of using H2O2 as pilot fuel, as opposed to other more conventional ones (e.g., diesel), is that it contains no carbon, and hence produces no CO2 and particulate matter (PM). The computational investigation was conducted with an advanced commercial stochastic engine model that has been previously validated. The investigation was primarily focused on assessing the effects of using hydrogen peroxide in aqueous solution as pilot fuel on engine efficiency, combustion phasing and NOx emissions. These three aspects were investigated over a range of engine speeds (750-1,750 rpm) in view of: (i) the variation of the mass of the directly injected (DI) aqueous solution (0.1-10 mg); (ii) the variation of the H2O2 share (15-50%) in the directly injected (DI) aqueous solution; (iii) the variation of the start of injection (from -20 to -4 CAD aTDC) and injection duration (1-8 CAD). There is a strong effect of the peroxide in advancing combustion timing (CAD50 is advanced by up to 15 CAD) and in decreasing combustion duration (CAD90-CAD10 decreases up to 10 CAD), and peroxide readily enables medium engine loads which are the ones investigated in this work. Indicated thermal efficiencies above 50% were readily achieved at all engine speeds and, with a 30 vol% peroxide share in the solution, the pressure rise rate was always below 30 bar/ms. However, the NOx emissions in all cases exceeded the IMO’s Tier III standard. Possible ways to tackle this would be either the use of exhaust gas recirculation, or optimisation of the injection strategy, or the use of aftertreatment. For most cases, on a volume basis, the required aqueous H2O2 amount is 3% of the main fuel while on an energy basis this translates to 1.1% of the main fuel blend. The results reported in this initial study are promising because it is possible to ignite a premixed charge on the basis of a small pilot volume of commercially available hydrogen peroxide solutions