An analysis of spray development with iso-octane, n-pentane, gasoline, ethanol and n-butanol from a multi-hole injector under hot fuel conditions

High-pressure multi-hole injectors for direct-injection spark-ignition engines offer some great benefits in terms of fuel atomisation, as well as flexibility in fuel targeting by selection of the number and angle of the nozzle’s holes. However, very few data exist for injector-body temperatures representative of engine operation with various fuels, especially at low-load conditions with early injection strategies that can also lead to phase change due to fuel flash boiling upon injection. The challenge is further complicated by the predicted fuel stocks which will include a significant bio-derived component presenting the requirement to manage fuel flexibility. The physical/chemical properties of bio-components, like various types of alcohols, can differ markedly from gasoline and it is important to study their effects in direct comparison to liquid hydrocarbons. This work outlines results from an optical investigation (high-speed imaging and droplet sizing) into the effects of fuel properties, temperature and pressure conditions on the extent of spray formation. Specifically, gasoline, iso-octane, n-pentane, ethanol and n-butanol were tested at 20, 50, 90 and 120 °C injector body temperatures for ambient pressures of 0.5 bar and 1.0 bar in order to simulate early homogeneous injection strategies for part-load and wide open throttle engine operation; some test were also carried out at 180 °C, 0.3 bar. Droplet sizing was also performed for gasoline, iso-octane and n-pentane using Phase Doppler and Laser Diffraction techniques in order to understand the effects of low- and high-volatility components on the atomisation of the multi-component gasoline. The boiling points and distillation curves of all fuels, their vapour pressures and bubble points, as well as density, viscosity and surface tension were obtained and the Reynolds, Weber and Ohnesorge numbers were considered in the analysis

Effect of Fuel Properties on Spray Development from a Multi-Hole DISI Engine Injector

Extensive literature exists on spray development, mixing and combustion regarding engine modeling and diagnostics using single-component and model fuels. However, often the variation in data between different fuels, particularly relating to spray development and its effect on combustion, is neglected or overlooked. By injecting into a quiescent chamber, this work quantifies the differences in spray development from a multi-hole direct-injection spark-ignition engine injector for two single-component fuels (iso-octane and n-pentane), a non-fluorescing multi-component model fuel which may be used for in-cylinder Laser Induced Fluorescence experiments, and several grades of pump gasoline (with and without additives). High-speed recordings of the sprays were made for a range of fuel temperatures and gas pressures. It is shown that a fuel temperature above that of the lowest boiling point fraction of the tested fuel at the given gas pressure causes a convergence of the spray plumes. Increasing the fuel temperature increases this convergence, whilst an associated increased rate of evaporation tends to reduce the penetration of individual plumes. The convergence increases gradually with increasing fuel temperature until all plumes combine to form a single wider plume with a penetration rate greater than that of the individual plumes. When all plumes are converged to form a single plume along a central axis to all the plumes, any further increase in fuel temperature at the given gas pressure acts to increase the rate of evaporation of the fuel. At experiments up to 180 °C fuel temperature and down to 0.3 bar absolute gas pressure, none of the tested fuels were found to spontaneously vaporize; all observed spray formations being a gradual evolution. Increasing the gas pressure at any given fuel temperature, leads to an increase in the boiling temperature of all components of that fuel and, hence, diminishes these effects. Copyright © 2007 SAE International

On the effect of ambient turbulence and thermodynamic conditions on fuel spray development for direct-injection spark-ignition engines

High-pressure multi-hole injectors for direct-injection spark-ignition engines offer certain flexibility in spray directionality by selecting the number and angle of the nozzle’s holes to suit the design of a particular combustion chamber. However, the spray’s pattern can change significantly for injector-body temperatures representative of real engine operation at low-load conditions with injection strategies in the early intake stroke. This is due to rapid phase change effects from flash boiling of the high-volatility components of gasoline. This work presents results from an optical investigation into the effects of injector-body temperature and back pressure on the pattern of spray formation, especially when coupled to different levels of ambient turbulence. Specifically, gasoline and iso-octane fuels were tested in the range of 20–120 °C injector-body temperatures and for ambient pressures of 0.5–5.0 bar. Additionally, the ambient turbulence was varied in the range 0–4 m/s to observe its effect on flash-boiling and non-flash-boiling sprays. Results from a combination of high-speed shadowgraphy and simultaneous Schlieren and Mie scattering optical techniques are presented in terms of imaged spray areas and plume penetration. Calculations of the Stokes number are also discussed with respect to turbulence and fuel properties. The results demonstrate a marginal effect of the degree of turbulence intensity on non-flash-boiling sprays that maintained their nominal plume directionality throughout the injection event. However, a significant effect on the spray’s penetration and mixing at conditions of fuel flash-boiling was observed with increasing levels of turbulence intensity; the collapsed pattern of the spray’s formation exhibited much faster dispersion and mixing

Optical Studies of Spray Development in a Quiescent Chamber and in a Direct-Injection Spark-Ignition Engine

The effects of fuel type and in-cylinder flow on spray formation from a multi-hole injector were studied by high-speed imaging techniques in a quiescent injection chamber and in a single-cylinder Direct-Injection Spark-Ignition (DISI) engine. To examine the effect of fuel volatility on spray formation, the injector was heated from 20 °C to 120 °C in the chamber for iso-octane and gasoline. The injection chamber was operated at 0.5 and 1.0 bar to mimic in-cylinder pressures for early injection strategies. Droplet sizing was also employed in the chamber using Phase Doppler Anemometry (PDA). Fuel-type and temperature effects were studied in-cylinder by operating the engine at 20 °C and 90 °C head temperature at 1500 RPM. For both sets of experiments, the study was carried out for two orthogonal views, relating to the tumble and swirl planes of in-cylinder flow motion. Spray formation was observed to be different for the two fuels, especially at high injector temperatures. Wetted footprint spray areas were calculated for both experimental setups. © IMechE 2007