Simón Martínez-Martínez

Liquid Sprays Characteristics in Diesel Engines

For decades, the process of injecting an active fluid (diesel fuel) into the thermodynamic behaviour of a working fluid (air or gas) has been a priority in the research of the phenomena that occur in combustion systems. Due to technological improvements it’s possible in present times to characterise the injection fuel process in such conditions that match those happening when the engine is running under standard conditions, hence the purpose of these studies, which focus in the achievement of a perfect mixture between the working and active fluids; as a result of this, a series of consequences are triggered that lead to an optimum combustion, and therefore in the improvement of the engines capabilities. In Diesel engines the combustion process basically depends on the fuel injected into the combustion chamber and its interaction with the air.

Effect of an ethanol–diesel blend on a common-rail injection system

This research paper presents a comparative experimental study for determining the functionality of a common-rail injection system used in light-duty diesel vehicles. Two Bosch fuel-injection systems were chosen to be tested using a low sulphur diesel fuel and an ethanol–diesel blend (7.7% v/v). Both systems were composed of a high-pressure injection pump Bosch (320 CDI), a common-rail and a Bosch piezoelectric fuel injector, and were tested during an accelerated durability test. In both cases, the injection systems were mounted in an injection test bench and run for 12 hours/day for 600 hours. An injection pressure of 1500 bar, a pump rotation speed of 2500 min−1 and an injection time of 1 ms were selected to simulate critical engine operating conditions. The selected test conditions were equivalent to driving a light-duty vehicle for over 120,000 km. This work employed several analysis equipment and techniques, including a surface tester for surface roughness characterization of the elements, an optical microscope for observation of the workpiece surface microstructure, a shadow comparator for geometrical characterization of elements, an analytical balance for weighing parts and, finally, a scanning electronic microscopy to determine nozzle dimensions. In both cases, the total fuel delivery was determined using an injection test bench. Results show that the use of the ethanol–diesel blend tested produced a similar effect on the durability of the injection pump parts as that produced when using diesel fuel. However, the effect on the injector nozzle was dissimilar.

Characterization of critical stretch rate using outwardly propagating spherical flames

Outwardly propagating spherical flames within a constant volume combustion chamber (CVCC) are studied to analyse the non-linear relationship between flame stretch and flame speed, enabling a critical appraisal of a methodology proposed for characterizing the critical stretch rate. Four fuels, namely methane, propane, methanol and ethanol in air, are chosen to investigate the correlation between maximum critical stretch rate and the flame extinction across a range of equivalence ratios at various ambient conditions in under-driven flames, and to compare the hypothesis against data from the traditional counter-flowing flame technique. Flame propagation is recorded via high-speed Schlieren photography, and low ignition energies are achieved via a variable capacitive-discharge supply, enabling the critical early stages of flame propagation, critical stretch rate and the sensitivity of the non-linear methodology to ignition energy to be systematically analysed. The non-linear methodology shows partial agreement with extinction stretch rate from counter flowing flames, particularly in the case of gaseous fuels. Although the fuel vapour data lies between previous extinction stretch rate measurements using the counterflowing flame methodology, and predictions from chemical kinetic schemes, a 40% deviation is observed. A mathematical expression was produced to determine the critical stretch at the specific conditions of the present work.

Effects of cavitation in common-rail diesel nozzles on the mixing process

A study to experimentally analyze the effect of cavitation on the mixing process in diesel nozzles was carried out. The mixing process was studied through the spray cone angle. It was characterized in two different scenarios: with the liquid length (nearly realistic conditions, that is, evaporative but non-reactive spray) and the heat release fraction (fully realistic conditions, that is, evaporative and reactive spray). In both studied scenarios, the increase in spray cone angle caused by the cavitation phenomenon, which leads to a better mixing process, has been confirmed. Nevertheless, when the variations of the effective injection velocity and the spray cone angle obtained by comparing a cylindrical nozzle (i.e. a nozzle that promotes the cavitation phenomenon) with a conical nozzle (i.e. a nozzle that inhibits this phenomenon) were analyzed together, it was found that, for the cases studied here, the mixing process worsens with the cylindrical nozzle.