The butanol isomers n-butanol and isobutanol as well as ethanol are among the biofuels most likely to be used for engine combustion and are likely to become more relevant as surrogate fuels or blend components in the future. To use the potentials of alternative fuels, the combustion mechanisms and, thus, burning behavior should be known. A key parameter for flame kinetic studies and combustion simulation is the laminar burning velocity. However, reproducible measurements of flame speeds of gasified liquid fuels are difficult. To reduce the scattering of experimental results to acceptable levels, there is a common research interest of several European institutes using so-called heat flux burners. In this work, a self-designed liquid fuel evaporation system has been combined with a precise droplet generator, which allows for measurements of adiabatic laminar burning velocity at elevated gas temperatures. The one-dimensional (1D) flame appears very stable, even close to its flammability limits. The boundary conditions are chosen to model exhaust gas recirculation (EGR) with different temperatures and compositions of the mixtures. The measurement data are compared to the corresponding results of other research groups, and the uncertainty of the burning velocity is estimated.

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The development of the injector nozzle is a dynamic area in regard of several technical aspects. At first, the internal flow influences the near-field spray characteristics via various phenomena such as cavitation and turbulence. However, these phenomena are not fully understood due to their extremely fast, complex and multiscale nature. Furthermore, it governs the spray targeting inside the combustion chamber. High-speed X-ray imaging of GDI injector nozzles is performed in this study. The experimental results presented are related to the internal flow and primary breakup of discharged liquid jets. The injectors used are equipped with nozzles made of aluminum which have been specially developed for these investigations to enhance optical accessibility. The visualization of the needle motion, in-nozzle flow and the primary breakup region provides several exciting observations. First, the needle lift tracking exhibits short overshooting right before the steady-state of the injection phase. This event leads to a short-term, however, significant change in the associated performance of the breakup. This phenomenon is found to be a consequence of the transient behavior of the in-nozzle flow. It is shown that under some circumstances hydraulic flip may occur during this overshooting period. The primary jet breakup region is visualized and evaluated by means of image processing. Thus, the transient behavior of liquid jet expansion is quantified in the vicinity of the nozzle. It is observed that the liquid jet direction deviates from the hole axis already at the nozzle outlet, which is caused by internal flow characteristics.

The effects of exhaust gas recirculation (EGR) on the laminar burning velocity of a commercial gasoline fuel-air mixture have been studied both numerically as well as experimentally at atmospheric pressure. The experiments have been performed using the heat flux burner method. For numerical simulation, a binary mixture of 95% iso-octane and 5% n-heptane (PRF95) is assumed to be the surrogate for the real world gasoline fuel. The numerical simulations have been carried out using a skeletal mechanism comprising of 171 species and 861 reactions for primary reference fuels. A correlation of laminar burning velocity of the commercial fuel is suggested based on experimental data for different EGR dilutions. The results show that the reduction in the laminar burning velocity caused by the EGR dilution can be recovered by the increase in the unburnt gas temperature. However, the rise in the unburnt gas temperature results in a trivial rise in the adiabatic flame temperature. The increase in the laminar burning velocity due to elevated unburnt gas temperature is principally attributed to the increase in thermal diffusivity of the fuel-air mixture, while the reaction rate has only a minor influence. The presence of CO 2 in the EGR influences the chemistry of the flame along with diluting it. Under stoichiometric conditions, the chemical and dilution effects toward the reduction in laminar burning velocity are almost equal.

Gasoline Direct Injection (GDI) systems have become a rapidly developing technology taking up a considerable and rapidly growing share in the Gasoline Engine market due to the thermodynamic advantages of direct injection. The process of spray formation and propagation from a fuel injector is very crucial in optimizing the air-fuel mixture of DI engines. Previous studies have shown that the presence of some cavitation in high-pressure fuel nozzles can lead to better atomization of the fluid. However, under some very specific circumstances, high levels of cavitation can also delay the atomization process; spray stabilization due to hydraulic flip is the most well-known example. Therefore, a better understanding of cavitation behavior is of vital importance for further optimization of next generation fuel injectors. In contrast to the abundance of investigations conducted on the inner flow and cavitation patterns of diesel injectors, corresponding in-depth research on the inner flow of gasoline direct-injection nozzles is still relatively scarce. In this study, the results of an experiment performed on real-size GDI injector nozzles made of acrylic glass are presented. The inner flow of the nozzle is visualized using a high-power pulsed laser, a long-distance microscope and a highspeed camera. The ambiguity of dark areas on the images, which may represent cavitation regions as well as ambient air drawn into the nozzle holes, is resolved by injecting the fuel both into a fuel or gas filled environment. In addition, the influence of backpressure on the transient flow characteristics of the internal flow is investigated. In good agreement with observations made in previous studies, higher backpressure levels decrease the amount of cavitation inside the nozzles. Due to the high temporal and spatial resolution of the experiment, the transient cavitation behavior during the opening, quasi-steady and closing phases of the injector needle motion can be analyzed. For example, it is found that cavitation patterns oscillate with a characteristic frequency that depends on the backpressure. The link between cavitation and air drawn into the nozzle at the beginning of injection is also revealed.