Particle/droplet Image Analysis Research Articles

A new aerosol delivery approach for enhanced long-term respiratory care in resource-poor settings

Continuous aerosol therapy is safe, superior, and the mainstay in the therapy of patients with severe asthma, cystic fibrosis, chronic obstructive pulmonary disease (COPD), and coronavirus disease (COVID-19). However, continuous nebulization has been perceived as highly expensive and labor-intensive, which often requires specialized medical equipment. Moreover, it is difficult to maintain consistent aerosol output and particle size delivery over an extended period without operator intervention. This work proposes a simple and reliable continuous nebulization method using a conventional gas jet nebulizer and intravenous (IV) bottle/bag. The present work reports detailed experimental studies on a gas jet nebulizer with Particle image velocimetry (PIV), Particle/droplet Imaging Analysis (PDIA), and Mie scattering techniques to demonstrate the feasibility of the proposed technique. The preliminary investigation shows that the proposed method provides continuous liquid output delivery without external supervision. The liquid delivery rate and mass median diameter (MMD) of the nebulizer mainly depend on the gas flow rate and suction height. The MMD of the primary generated droplets is reported to vary between 100 and 230 μm for a ± 10 cm suction height and 500–1000 mlph nebulization gas flow rate. Most importantly, the nebulizer spray angle, stability, droplet size distribution, and the axial and radial velocities of the droplets are marginally affected by the suction height. Therefore, the proposed system is a versatile, safe, and cost-effective method of continuous nebulization therapy, especially in resource-poor countries or contagious disease outbreak situations.

Neural networks for classification and segmentation of thermally-induced droplet breakup in spray-flame synthesis

Spray-flame synthesis (SFS) enables one-step production of functional metal-oxide nanoparticles from inexpensive precursors such as metal salts. Precursor-laden droplets show thermally-induced breakup, i.e., puffing and micro-explosion, considered a key step in SFS. In this work, shadowgraphy images of droplets are investigated with neural networks with the aim of extracting quantitative data on this breakup process. Faster and Mask region-based convolutional neural networks (R-CNNs) were applied to segment in-focus droplet shadowgraphs (Mask R–CNN) and to distinguish regular from disrupting droplets and detect sequences of consecutive droplet shadowgraphs (Faster R–CNN). The networks were trained with about 400 manually annotated images containing a total of about 1200 objects. Precision and recall of the trained networks reach 80% and 90%, respectively. The results from the two networks were combined and compared with those from conventional particle/droplet image analysis (PDIA). Mask R–CNN and PDIA identify similar droplets as being in-focus and segment similar regions of the droplets. Puffing or micro-explosion sometimes leave behind secondary droplets that are too small or defocused for reliable segmentation. Such shadowgraphs are classified erroneously by PDIA. In contrast to this, Faster R–CNN is more sensitive as it does not rely on the segmentation and thus classifies such low-contrast shadowgraphs correctly. Therefore, the CNNs find on average 30% higher droplet-disruption probabilities than PDIA.

Experimental Investigation of Kerosene Droplet Distribution in a Linearized Rotating Detonation Engine

ABSTRACT The atomization and mixing process in a linearized rotating detonation engine supplied with non-premixed kerosene was optically analyzed by experiment. Schlieren, simultaneous LIF/Mie technique and particle/droplet image analysis (PDIA) system were applied to study flow field structure and spray properties under various conditions, including air flow rate, fuel flow rate and flow velocity at injector position. Aerodynamic shearing force and fuel injection pressure contribute to the refinement and uniformity of the spray. The distribution of fuel in the combustor has obvious stratification, which makes the local equivalence ratio higher than the set global equivalence ratio. Compared with full-scale RDE experiments, the detonation wave exists in a dual-wave collision mode. The increased kerosene flow rate refines the droplets, which raises the detonation wave velocity. Furthermore, the detonation wave will propagate more stably due to the slower airflow velocity at higher combustor pressure.

Spray characteristics of an air-assisted electrostatic atomiser

The spray characteristics of an air-assisted electrostatic atomiser are experimentally investigated using a shadowgraphy particle/droplet image analysis (PDIA) technique. Tests are conducted for varied rates of liquid- and airflow, with and without a voltage applied to the nozzle electrode. The found droplet sizes neatly match the Rosin–Rammler distribution, and an expression for the mean diameter as a function of the flow rates is given. Notably, the electrode voltage (up to 40 kV) has no measurable impact on the droplet size and velocity, and the energy efficiency of the sprayer is found to decrease with increases in both liquid- and airflow.

Experimental investigation on spray and ignition characteristics of plasma actuated bluff body flameholder

Stable combustion of aero-engines and ramjet combustors is greatly dependent on the quality of atomization. It is quite difficult to achieve wider ignition boundary and good combustion performance under low pressure and low temperature airflow, because the quality of fuel atomization is comparative bad and there is no enough surface area for fuel droplets to mix with surrounding air and evaporate. Internal mechanism of how plasma assisted ignition on spray performance in model aero-engine combustors and ramjet combustors remains not clear. In this study, a novel plasma-actuated bluff-body flameholder is proposed to help improve the quality of fuel atomization and thus enhance the ignition performance and stable combustion of original bluff-body flameholder. Spray and atomization properties of aviation kerosene (RP-3) were investigated under various operating conditions including inlet pressure, inlet temperature and gliding arc plasma actuation. A rotating arc discharge plasma column could be formed during the high-voltage tungsten electrode and the fins of bluff-body flameholder. Macroscopic as well as microscopic spray properties was analysed through simultaneous LIF/MIE technique along with particle/droplet image analysis (PDIA) system. Flame ignition limit at different inlet temperature was conducted under combustor inlet Mach number of 0.2. Results show that mean drop diameters were decreased with increase of inlet temperature and inlet pressure. Gliding arc plasma actuation help fuel injected from bluff-body flameholder breakup into smaller droplets and improve uniformity of fuel spray through heating and transport effect. With actuation of gliding arc plasma, Sauter mean diameter (SMD) was minished by 13%∼20% at inlet pressure of 30 kPa, while droplet uniformity index was increased by around 21.8%. Due to better fuel atomization quality together with more active components generated by gliding arc plasma, flame ignition limit of bluff-body flameholder was obviously extended by about 13%∼30%. The gliding arc plasma was verified to promote fuel droplets atomization and to achieve homogeneous distribution under low temperature and pressure, which is beneficial to wider flame ignition and stabilization boundary.

Experimental investigation of multi-phase hydrodynamics and bubble-particle interactions in a Wemco 56 flotation cell

Performance of flotation cells heavily relies on their hydrodynamics inside cells and interactions among the solid, liquid and gas phases. The flotation process in conjunction with the bubble-particle interactions in three-phase flow were experimentally investigated in an industrial Wemco 56 cell. Various methods were developed to measure and analyse the flotation process, in which the velocity field of liquid phase was measured using Particle Image Velocimetry (PIV). Particle/Droplet Image Analysis (PDIA) technique was developed to capture and measure bubble sizes, while a conductivity-based probe system was designed to evaluate the mixing status of solid, liquid and gas phases. The flotation kinetics were found relatively inhomogeneous and anisotropic in most regions, while possible flow short-circuiting was identified near bottom corner of the tank. The bubble mix was found insufficient near the cell bottom, although void fractions near the bottom slightly increased after adding particles. The investigation revealed significant impacts of the solid phase, which stimulated bubble to breakup and reattach more actively and promoted bubbles to penetrate further downwards to the bottom. A solid deposition layer of 30 mm was observed near bottom of the Wemco 56 cell, which requires optimisation of draft tube and false bottom designs.

Experimental investigation of spray characteristics of gliding arc plasma airblast fuel injector

High atomization quality plays a vital role in combustion performance enhancement for aero-engines and ramjets. Low enthalpy and low pressure at low flight Mach number result in poor atomization quality of airblast fuel injector. Underlying mechanism of how plasma assisted combustion on spray characteristics still remains unclear. In present study, a novel gliding arc plasma airblast fuel injector is proposed for atomization quality improvement of airblast fuel injector in order to achieve high combustion efficiency, low pollutant emission, and to prolong life of injectors. Spray and atomization characteristics of aviation kerosene (RP-3) under different working conditions which includes gliding arc plasma excitation, air flow velocity and air/fuel ratio were investigated. A string-like gliding arc discharge plasma column was generated between the two electrodes mounted at the exit port plane of plasma airblast fuel injector. Macroscopic and microscopic spray characteristics were studied by simultaneous LIF/MIE technique and particle/droplet image analysis (PDIA) system. Results reveal that mean droplet size were decreased with increase of air flow velocity and air/fuel ratio. Influenced by the thermal and transport effect of gliding arc plasma excitation, more homogeneous fuel spray with smaller mean drop size and greater spray cone angle was witnessed. Sauter mean diameter was decreased by around 50% at 17 m/s, while droplet uniformity index and spray cone angle were increased by up to 24.6% and 35%, respectively. The gliding arc plasma mainly take effect on reducing mean droplet size of kerosene in the near-field spray (<20 mm) which is very near from the ignitor to improve high initial evaporation rates for rapid ignition and combustion efficiency improvement.

Estimation of measurement error and depth of field in PDIA experiments: a comparative study using water droplets and a calibration target

The particle/droplet image analysis (PDIA) technique is often used for droplet sizing in sprays. Successful use of PDIA for drop size measurement in sprays mandates careful calibration, and determination of the depth of field (DOF) for particles of different size classes. This is typically done with a calibration target that has circles etched on it. In the present study, a calibration experiment was performed with a calibration target as well as droplets, to evaluate the uncertainties in the measured sizes and also to compare the measured DOF values. A continuous-jet droplet generator was used to produce mono-disperse droplets of sizes ranging from 54–393 µm, and the calibration glass plate used contained circles of sizes ranging from 20–400 µm. Images of these were captured using a CCD camera equipped with a long-distance microscope, and were processed using a code written in MATLAB®. Differences in the measured sizes of droplets and circles, and their DOF values are reported. It was observed that the use of the calibration target led to an underestimation of the error in droplet size measurements, and an overestimation of the DOF. For the droplets, the measurement error was observed to be less than 5%, with the parameters chosen.

Planar drop-sizing and liquid volume fraction measurements of airblast spray in cross-flow using SLIPI-based techniques

This paper presents planar measurements of Sauter mean diameter (SMD) and liquid volume fraction distributions of airblast spray injected into cross-flow. The experiments are conducted using a combination of structured laser illumination planar imaging with laser sheet drop-sizing (SLIPI-LSD) and particle/droplet imaging analysis (PDIA) techniques. Effect of gas to liquid mass ratio (GLR) and cross-flow velocity (Ucross) is studied. Planar SMD distribution at low GLR improved with increase in Ucross due to secondary atomization of large droplets. Uniform SMD distribution in a range of 10–20 µm is observed for GLR more than 3. The distribution of liquid volume fraction at low GLR condition shows poor dispersion with most of the liquid concentrated near the injector. The liquid volume fraction distribution improves with increase in GLR and better dispersion is observed for GLR more than 3 and two-phase momentum ratio (q2) greater than 13.06. Spatial bifurcation in liquid fraction is found for high GLR conditions. The SMD in the range of 10–20 µm and uniform distribution of liquid are observed for GLR more than 3 and q2 > 25.6.

Planar liquid volume fraction and SMD distribution of Jatropha vegetable oil spray: effect of ethanol blending and GLR

This research paper presents the planar distribution of Sauter Mean Diameter (SMD) and liquid volume fraction in airblast sprays of Jatropha vegetable oil. The effect of ethanol blending at different gas to liquid mass ratios (GLRs) is presented. The planar SMD distributions are obtained using Structured Laser Illumination and Planar Imaging-Laser Sheet Drop sizing (SLIPI-LSD) and Particle/droplet Imaging Analysis (PDIA) techniques. The straight vegetable oil (SVO) spray showed poor atomization at GLR 1, which rose with increasing GLR. The blending of ethanol significantly improved the atomization of SVO even at GLR 1 condition. The liquid volume fraction distribution increased with higher GLR and with the increase in the percentage of ethanol in the blend. The impact of the increase in ethanol on drop size is small at GLR of 5. The E30 blend showed uniformly distributed liquid in the spray plane with uniform SMD distribution in the range of 50 \(\upmu \)m at GLR 5.

Time-resolved droplet size and velocity distributions in a dilute region of a high-pressure pulsed diesel spray

The principal objective of the present work is to experimentally investigate the time-resolved spray characteristics. Droplets data in a dilute region of a high-pressure diesel spray were obtained by employing the PDIA (particle/droplet image analysis) method with double pulse laser illumination. Eulerian specification was adopted to describe the transient spray microscopic behavior within a fixed test window at ten representative instants after triggering the injection. The experimental results indicate that the transient spray evolution can be characterized in three distinct stages. During stage I (the latency stage), the spray tip develops and reaches the test location, but no discrete droplets were clearly observed. During stage II, the spray passes through the test window, from which discrete droplets are observed to disperse in the dilute region and the SMD of the droplets increases rapidly. During stage III, bulk spray disappears in the test window and only discrete droplets were observed. The SMD of the droplets is decreased to a “steady-state” value. Based on these sampled and processed data, the droplet size distribution functions were obtained and compared with the Rosin-Rammler and the Nukiyama-Tanasawa function. Finally, the Stokes number and the Weber number of each droplet were determined, and the movement of the droplets were analyzed. The measured time dependent droplet behaviors are believed to provide important data for spray modeling and simulation.

Planar liquid volume fraction measurements in air-blast sprays using SLIPI technique with numerical corrections

A methodology to improve the accuracy of liquid volume fraction measurement in a dense spray is presented. A combination of experimental technique, structured laser illumination and planar imaging (SLIPI) and numerical corrections is used to overcome losses in conventional planar laser-induced fluorescence (PLIF) imaging. A quantitative distribution of liquid volume fraction in a plane is obtained using corrected SLIPI–PLIF signal and PDIA (particle/droplet imaging analysis) technique. The methodology is applied to air-blast sprays for GLRs (gas to liquid mass ratio) 1, 2.5 and 4. The effect of multiple scattering is significantly high in the conventional PLIF signal imaging. A hollow cone spray geometry is observed at a GLR of 1 using the improved imaging technique. An increase in GLR from 1 to 4 leads to uniform distribution of liquid in a spray plane. A significant contribution of multiple scattering ( $$\sim$$ 62%) is observed in the conventional PLIF signal at GLR 4 along the axis of the spray. The symmetry in the SLIPI–PLIF signal is restored using the numerical corrections. The liquid volume fraction measurements from SLIPI–PLIF technique are further improved with the numerical corrections.

Experimental investigation on effect of ethanol and di-ethyl ether addition on the spray characteristics of diesel/biodiesel blends under high injection pressure

In this work, a comprehensive experimental investigation on spray characteristics of four blended fuels, including diesel (D100), diesel-biodiesel (DB), diesel-biodiesel- ethanol (DBE), and diesel-biodiesel-diethyl ether (DBDE) has been conducted by using high pressure common rail injection system (up to 200 MPa). The transient spray behavior under various conditions was recorded by high speed photography with scattering light illumination. It is shown that higher injection pressure significantly accelerates the spray tip penetration (STP) evolution due to increased inertia of spray while increase in ambient pressure reduces the STP evolution due to higher gas resistance. With the addition of diethyl ether (DEE) into biodiesel, the STP of blended fuel tends to go down and corresponding projected area increases a lot when compared to DB. By means of particle droplet image analysis (PDIA) optical diagnostic method, spray microscopic parameters such as Sauter Mean Diameter (SMD), droplet diameter distribution probability curve, cumulative volume curve and characteristic diameter have been investigated. Results show that both the injection pressure and ambient pressure have significant influence on the spray microscopic characteristics. In addition, for fixed injection pressure and ambient pressure, when DEE is added into DB blends, the number fraction of smaller droplets increases, though the statistic diameter with peak probability is fixed at a certain value. Furthermore, SMD of the four tested fuels decreases sequentially in the order of DB, D100, DBE, and DBDE, indicating that DEE addition favors the atomization process.

Experimental study on the effect of injector nozzle K factor on the spray characteristics in a constant volume chamber: Near nozzle spray initiation, the macroscopic and the droplet statistics

In this work, the effects of the injector K factor on the spray characteristics have been investigated by using a high pressure common rail injection system and a constant volume chamber. The near nozzle region spray tip behavior, the spray macroscopic characteristics, and the droplet statistics in a fixed spray location is sequentially examined. Specifically, in the near nozzle region, laser pulse illumination and microscopic imaging technique was used to capture the very initial spray evolution morphology and it is found to take on the form of a mushroom like structure which quickly breaks up. Increasing K factor advances the spray tip evolution and favors the formation of the shockwave which might be caused the accelerated nozzle inner flow. For different K factor nozzles, the spray tip penetration (STP) evolution before the primary breakup is all found to include two sub-stages: in the very initial stage when the needle valve open is relatively small, the breakup of the mushroom like tip results in a slightly decelerated STP evolution. Subsequently, when the needle valve is fully opened, the STP evolution is gradually accelerated by the increased mass flux. The classic Hiroyasu and Arai [1] empirical model, which shows constant STP evolution speed before the primary breakup, is then refined to account this unsteady STP evolution behavior. Secondly, the spray macroscopic behavior data such as the spray tip penetration and the spray cone angle from varying K factor nozzles were collected by high speed visualization. It is found that as the K factor is increased, the STP evolution is accelerated and spray cone angle decreases. The classic model for the STP by Hiroyasu and Arai [1] which is applied K=0 nozzle was extended to accommodate the effect of K factor on the STP evolution after the primary breakup and the revised empirical model show perfect performance in predicting the STP behavior after the primary breakup for all different K factor nozzles. Finally, by using the particle/droplet image analysis (PDIA) system, the droplet statistics and the Sauter Mean Diameter (SMD) that characterize the atomization behavior at a certain spray location were obtained. It is seen that high K factor nozzle yields a slightly smaller SMD and it’s believed to enhance the atomization process. However, our experimental results show that this K nozzle effect is relatively weak and it vanishes for nozzles with larger outlet diameter.

Effect of polyoxymethylene dimethyl ethers addition on spray and atomization characteristics using a common rail diesel injection system

PODE is named for the mixture of polyoxymethylene dimethyl ethers. Recently, it is used as diesel oxygen additive to reduce diesel engine smoke. In this study, the effect of PODE addition on the spray and atomization of diesel spray was investigated by using a high pressure common rail system. The spray tip penetration (STP), the spray cone angle and the spray projected area were extracted at the injection pressure of 60, 90 and 120MPa and the ambient pressure of 4MPa through a high speed photographic device. The results show that as PODE is added into diesel, the STP is slightly decreased and the average spray cone angle and projected area are slightly increased. In addition, the microscopic spray characteristics such as statistical droplets size distribution and characteristic diameters and relative size range were obtained by a particle/droplet image analysis (PDIA) technique. The results shows that as PODE is added into diesel, the droplets number tends to be uniformly distributed around 12–20μm range and smaller characteristic diameters are observed and the relative size range keeps constant. All of such characteristics of the spray indicate that PODE addition can better the atomization of diesel spray.

Experimental investigation on spray and atomization characteristics of diesel/gasoline/ethanol blends in high pressure common rail injection system

The effects of gasoline and ethanol addition on the spray and atomization characteristics of diesel spray from a common rail injection system, was investigated in a constant volume chamber at different ambient and injection pressures. The fuel spray evolution process was recorded with high spatial and time resolution and the corresponding spray tip penetration (STP), the cone angle were extracted. The results show that increased gasoline proportion in the test blends causes decreased STP and increased spray cone angle. Additionally, the microscopic spray characteristics such as the local average droplet diameter and statistical size distributions were measured by particle/droplet image analysis (PDIA) technique. As gasoline blending ratio increases, significantly smaller droplet size was observed which indicates that the spray breakup and atomization processes were promoted. Further adding ethanol slightly increased the droplet size, but it is still much smaller than the droplet size of neat diesel spray. Moreover, the local droplet size increases along the radial direction but the local droplet volume fraction and normalized droplet number density decreases, indicating a reduced fuel concentration along the radial direction. Along the axial direction, the droplet size, the local droplet volume fraction and the normalized droplet number density were almost constant.

Airblast spray in crossflow – Structure, trajectory and droplet sizing

This study reports results of an experimental investigation of airblast spray of water and ethanol in crossflow. Laser shadowgraphy and Particle/Droplet Imaging Analysis (PDIA) are used to derive spray trajectory and drop size information while Particle Tracking Velocimetry (PTV) is used to measure droplet velocities. A new phenomenon of spray bifurcation is observed for low Gas to Liquid Ratio (GLR) cases. The reasons for the spatial bifurcation can be attributed to a combination of reasons. These are (a) presence of large ligaments and droplets in the near-nozzle region for low GLRs (b) secondary breakup experienced by ligaments/droplets leading to formation of a large number of small droplets, and (c) the crossflow causing differential dispersion of the small and large droplets. A novel correlation for spray trajectory is proposed incorporating the momentum ratio and liquid surface tension. This correlation is shown to be effective in predicting the non-linear spray trajectory over a large range of conditions for not only water but ethanol and Jet-A also. It is observed that the larger droplets penetrate further into the crossflow, in the direction of injection. Thus, with increase in height of the measurement location from the injection plane, the droplet Sauter Mean Diameter (SMD) is found to increase. Moreover, as the droplets travel downstream in the crossflow direction, the droplet SMD is observed to decrease. The effect of drag is assessed by comparing velocity of different sizes of droplets at various locations. Smaller droplets are entrained into the crossflow at much lower elevations, whereas larger droplets tend to penetrate further into the crossflow.

EXPERIMENTAL STUDIES ON AIR-ASSISTED ATOMIZATION OF JATROPHA PURE PLANT OIL

The present study focuses on exploring air-assisted atomization strategies for effective atomization of high-viscosity biofuels, such as pure plant oils (PPOs). The first part of the study concerns application of a novel air-assisted impinging jet atomization for continuous spray applications, and the second part concerns transient spray applications. The particle/droplet imaging analysis (PDIA) technique along with direct imaging methods are used for the purpose of spray characterization. In the first part, effective atomization of Jatropha PPO is demonstrated at gas-to-liquid ratios (GLRs) on the order 0.1. The effect of liquid and gas flow rates on the spray characteristics is evaluated, and results indicate a Sauter mean diameter (SMD) of 50 mu m is achieved with GLRs as low as 0.05. In the second part of the study, a commercially available air-assisted transient atomizer is evaluated using Jatropha PPO. The effect of the pressure difference across the air injector and ambient gas pressure on liquid spray characteristics is studied. The results indicate that it is possible to achieve the same level of atomization of Jatropha as diesel fuel by operating the atomizer at a higher pressure difference. Specifically, a SMD of 44 mu m is obtained for the Jatropha oil using injection pressures of <1 MPa. A further interesting observation associated with this injector is the near constancy of a nondimensional spray penetration rate for the Jatropha oil spray.

Effect of di-n-butyl ether blending with soybean-biodiesel on spray and atomization characteristics in a common-rail fuel injection system

In this work, the spray and atomization characteristics of soybean biodiesel, di-n-butyl ether (DBE)/biodiesel blends and 0# diesel were investigated by using a high pressure common-rail injection system. The macroscopic spray characteristics such as the spray tip penetration (STP), the cone angle and the spray projected area were obtained from the spray images captured through high speed schlieren photography. The results show that as DBE is blended into biodiesel, the STP is decreased and the spray cone angle, projected area are increased and when the DBE volume fraction in the DBE/biodiesel blends reaches 30%, the STP, the spray cone angle and the projected area are comparable to that of diesel. For all the tested fuels, the microscopic spray characteristics such as the Sauter Mean Diameter (SMD) and statistical size distributions were measured by particle/droplet image analysis (PDIA) technique. The droplets number density distribution shows that for all the tested fuels, the region near the central of spray has the largest droplets number density and it decreases sharply as the position shifts from the center to the edge of the spray. As DBE is blended into biodiesel, smaller SMD is observed, which indicates that DBE addition can promote the atomization of biodiesel.

Study of liquid fuel transport in a small carburetted engine in the context of cold-start HC emission control

In the present study, a detailed visualization of the transport of fuel film has been performed in a small carburetted engine with a transparent manifold at the exit of the carburettor. The presence of fuel film is observed significantly on the lower half of the manifold at idling, while at load conditions, the film is found to be distributed all throughout the manifold walls. Quantitative measurement of the fuel film in a specially-designed manifold of square cross section has also been performed using the planar laser-induced fluorescence (PLIF) technique. The measured fuel film thickness is observed to be of the order of 1 mm at idling, and in the range of 0.1 to 0.4 mm over the range of load and speed studied. These engine studies are complemented by experiments conducted in a carburettor rig to study the state of the fuel exiting the carburettor. Laser-based Particle/Droplet Image Analysis (PDIA) technique is used to identify fuel droplets and ligaments and estimate droplet diameters. At a throttle position corresponding to idling, the fuel exiting the carburettor is found to consist of very fine droplets of size less than 15 μm and large fuel ligaments associated with length scales of the order of 500 μm and higher. For a constant pressure difference across the carburettor, the fuel consists of droplets with an SMD of the order of 30 μm. Also, the effect of liquid fuel film on the cold start HC emissions is studied. Based on the understanding obtained from these studies, strategies such as manifold heating and varying carburettor main jet nozzle diameter are implemented. These are observed to reduce emissions under both idling and varying load conditions.