Pre-chamber Ignition System for Homogeneous Lean Combustion Processes with Active Fuelling by Volatile Fuel Components

The combustion of homogeneous lean or diluted mixtures would significantly increase the efficiency of SI engines, but common spark ignitions systems are incapable to ignite these mixtures. Pre-chamber ignition systems burn a small portion of the charge in a separated chamber, which is connected to the main chamber by multiple small orifices. The combustion in the pre-chamber generates hot gases, which penetrate the main chamber, increase the turbulence and ignite the mixture on multiple sites. This leads to an increased turbulent flame speed and an extended lean and dilution limit, if the mixture in the prechamber is kept stoichiometric. Pre-chamber ignition systems have been investigated since the 1970s for passenger cars and are today commonly used in large gas engines. The adaption of the prechamber fuelling system to passenger car engines is not trivial, due to the problematic mixture preparation in the pre-chamber. Injection of a gaseous fuel in the pre-chamber would require a second fuel system with high pressure storage tank. Liquid gasoline direct injection in the pre-chamber is difficult due to the small space available for mixture preparation and the high surface to volume ratio, resulting in insufficient evaporation especially during cold start conditions. To overcome this problem, we developed a pre-chamber ignition system with active fuelling by volatile fuel components, which facilitates the integration in passenger cars. The system uses a mixture of air saturated with gasoline vapour for the pre-chamber fuelling. This gaseous mixture is typically found in the fuel tank above the liquid level and hence available in passenger cars. Former publications by the authors already proved the ability to enrich the pre-chamber and stabilize the combustion at homogeneous lean operation. Recent work focused on the optimization of the pre-chamber fuelling system and the pre-chamber geometry. To simulate the fuel tank atmosphere under different environment settings, a system was built, which saturates air with volatile gasoline components. This mixture gets compressed and dosed to the pre-chamber by a solenoid valve. Multiple prototypes of the pre-chamber with different volumes and geometry were investigated in a full engine at characteristic operating points regarding thermal efficiency, combustion process and emissions. These prototypes incorporate a spark plug, fuelling valve, thermocouple and pressure transducer. The results show the ability to ignite homogeneous lean mixtures with λ ≈ 2.0. Optimum operation was achieved with λ = 1.85 at 4.5 bar IMEP and 1500 rpm. This operating point showed an efficiency gain of 15 % compared to stoichiometric spark plug operation and NOx emissions below 20 ppm. The technology enables the usage of actively fuelled pre-chambers in passenger cars. The volatile fuel components for the pre-chamber fuelling are available in the fuel tanks atmosphere and thus allow a single fuel solution with inexpensive components

Cross-plane PIV for the characterization of low viscosity viscoelastic fluids

Thermal management of electric high-power devices is more important than ever. The electrification of the transport sector and increasing High-Performance-Computing (HPC) are the main driving forces for the increasing demands. Therefore, immersion cooling concepts arise, where the cooling liquid is in direct contact with the heat source, e.g., the CPU of a computer or the cell of a battery module. The main advantage is to eliminate the heat conduction through a cooling plate or heat pipes in the heat transfer path, which increases cooling efficiency. The downside is, that the cooling system could get very bulky, which is not very critical in huge HPC centers but is a showstopper for mobile applications. The project IBAT investigates radically new dielectric cooling fluids, funded by the EU program horizon 2020. These oil-based synthetic liquids are of very low viscosity. This allows very small gaps between battery cells resulting in a compact battery module design. Naturally appearing vortices at the cell edges quickly dissolve due to the low viscosity liquids. A stable boundary layer forms on the cell surface diminishing the heat transfer. To counteract this phenomenon linear vortex generators (LVGs) could be applied to the cell surface. The downside of this solution is increased flow resistance and thus higher pumping losses in the cooling circuit, partly canceling out the advantages of the low viscosity liquids. The more sophisticated solution to break up the thermal boundary layer is to stabilize the natural vortices. This is achieved by adding long polymer chains to the fluids, which give them viscoelastic properties. The initial results are very promising but show that the fluid properties must be tailored to the specific geometry. The catch is that the viscoelastic fluid properties of such low-viscosity fluids cannot be measured with conventional rheometers. A workaround is provided by optical flow analytics in benchmark geometries. One method is the observation of cross- plane vortices in a 180° bend with circular cross-section. The authors describe and discuss the challenges and uncertainties of cross-plane PIV for such experiments

Flashboiling atomization in nozzles for GDI engines

[EN] Flashboiling denotes the phenomenon of rapid evaporation and atomization at nozzles, which occurs when fluids are injected into ambient pressure below their own vapor pressure. It happens in gasoline direct injection (GDI) engines at low loads, when the cylinder pressure is low during injection due to the closed throttle valve. The fuel temperature at the same time approaches cylinder head coolant temperature due to the longer dwell time of the fuel inside the injector. Flash boiling is mainly beneficial for atomization quality, since it produces small droplet sizes and relative broad and homogenous droplet distributions within the spray. Coherently, the penetration depth normally decreases due to the increased aerodynamic drag. Therefore the thermal properties of injectors are often designed to reach flash boiling conditions as early as possible. At the same time, flash boiling significantly increases the risk of undesired spray collapsing. In this case, neighbouring jets converge and form a single jet. Due to the now concentrated mass, penetration depth is enhanced again and can lead to liner or piston wetting in addition to the overall diminished mixture formation. In order to understand the underlying physics, it is important to study the occurring phenomena flashboiling and jet-to-jet interacting i.e. spray collapsing separately. To this end, single hole injectors are built up to allow for an isolated investigation of flashboiling. The rapid expansion at the nozzle outlet is visualized with a microscopic high speed setup and the forces that lead to the characteristic spray expansion are discussed. Moreover, the results on the macroscopic spray in terms of penetration, cone angles and vapor phase are shown with a high speed Schlieren setup. Resulting droplet diameters and velocities are measured using LDA/PDA. As a result, we find a comprehensive picture of flash boiling. The underlying physics can be described and discussed for the specific case of high pressure injection at engine relevant nozzle geometries and conditions, but independently from neighbouring jets. These findings provide the basis to understand and investigate flashboiling and jet-to-jet interaction as distinct, but interacting subjects rather than a combined phenomenon.The authors would like to thank Continental for providing the experimental injectors used in this paper and Specialised Imaging for providing parts of the equipment used for the shown measurements. Additionally the authors gratefully acknowledge the financial support for parts of their work from the Erlangen Graduate School in Advanced Optical Technologies (SAOT) within the framework of the German Excellence Initiative by the German Research Foundation (DFG).Bornschlegel, S.; Conrad, C.; Eichhorn, L.; Wensing, M. (2017). Flashboiling atomization in nozzles for GDI engines. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 321-328. https://doi.org/10.4995/ILASS2017.2017.4750OCS32132

Pharmacodynamic Effects of an Angiotensin II Receptor-Antagonist in Phase I—Comparison between Healthy Subjects and Patients with Hypertension

Biomarkers are increasingly used to provide decision making data early in phase I by showing Proof of Mechanism or Proof of Concept (PoM/PoC). For antihypertensive agents, the administration of multiple doses (md) to hypertensive patients is assumed to be necessary for an early go/no-go decision. We compared the effects of an Angiotensin II receptor antagonist (ARA) on Plasma Renin and blood pressure (BP) following an oral single dose (sd) and once daily md for seven days to healthy volunteers and patients with essential hypertension (diastolic BP 95 mmHg to 114 mmHg; systolic BP 130 mmHg to 200 mmHg). Methods: 5–12 healthy male subjects/dose received 10 mg to 300 mg ARA sd and 50 to 300 mg md for 7 days; patients (9–10/dose) received 20 mg–400 mg ARA for 7 days. The studies were designed as randomized, single-blind, placebo-controlled, group comparison or crossover dose-escalation studies. Plasma Renin and BP were monitored up to 24 hours after dosing. Results: Plasma Renin showed a high interindividual variability in both healthy volunteers and patients. Healthy subjects showed a dose- and time-related increase in plasma Renin after sd from 40 mg to 300 mg and md of 50 mg to 300 mg (p < 0.05 for doses of 200 mg and 300 mg). In patients, increases in plasma Renin occurred at 8 hours and beyond starting at sd of 100 mg and md of 50 mg (p < 0.05 for the dose of 400 mg). While healthy volunteers showed no relevant decrease in BP, in hypertensive patients a reduction in BP in doses of 100 mg to 400 mg occurred (p < 0.05); effects were more pronounced after md compared to sd. Conclusion: Early PoM for an antihypertensive agent can be shown by use of laboratory biomarkers following sd to healthy subjects. PoC can be achieved after sd in hypertensive patients. Administration of sd to healthy volunteers is sufficient for an early go/no-decision

The liquid penetration of diesel substitutes

[EN] Diesel fuel consist of several hundreds of substances on organic basis. Experimental and numerical investigations of this multicomponent fuel are hard to interpret in detail, since the behavior of the multicomponent mixture is complex. Physical and chemical data of this system is not available under engine relevant conditions. Instead, fundamental research substitutes diesel with pure substances, where a big database exists. Prior work already showed, that overall spray propagation (including vapor phase) is nearly independent on the injected fuel. This is due to the high air entrainment at present diesel engine conditions (very high injection pressure and dense ambient atmosphere). The high air entrainment shortly behind the nozzle exit (within the first 5 mm penetration) creates a situation where properties of the ambient gas dominate the spray propagation resulting in similar mass and momentum distributions even for different fuels, if the injection conditions are kept constant. On the other hand, the liquid length is clearly different for different fuels, so that location and time of the phase change differ with consequences on the time available for mixture formation in the gas phase. The paper describes the liquid length as a function of the enthalpy necessary for the phase transition (given by the fuel and fuel temperature at injection) and the injection conditions (ambient gas properties, injector design and injection pressure). We compare two different models describing the enthalpy balance. Siebers et al. presented “Model I”, where mass transfer dominates the enthalpy transfer and evaporation takes place. In our own “Model II” evaporation is suppressed, resulting in a heat transfer driven enthalpy transfer without mass transport. The calculations are validated with experimental data. The liquid length is optically accessible by Mie-Scattering imaging techniques, the complete spray evolution by Schlieren technique. The experimental study was carried out in the high-pressure combustion vessel “OptiVeP” at FAU. The data shown in this paper derived from measurements with dodecane injected at 1200 bar into 613 K ambient. The ambient pressure varies from 1 – 10 MPa. A Continental research injector with a 115 µm hole and L/D of 6.5 was used. Nitrogen atmosphere suppressed ignition. Increasing the ambient pressure leads to a change in the mechanism in phase transition. It switches from a mass transfer dominated regime to a heat transfer dominated regime at high ambient pressures.Riess, S.; Weiss, L.; Rezaei, J.; Peter, A.; Wensing, M. (2017). The liquid penetration of diesel substitutes. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 1060-113. https://doi.org/10.4995/ILASS2017.2017.4764OCS106011

High Speed Shadowgraphy of Transparent Nozzles as an Evaluation Tool for In-Nozzle Cavitation Behavior of GDI Injectors

[EN] 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.Mamaikin, D.; Knorsch, T.; Rogler, P.; Leick, P.; Wensing, M. (2017). High Speed Shadowgraphy of Transparent Nozzles as an Evaluation Tool for In-Nozzle Cavitation Behavior of GDI Injectors. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 1027-1034. https://doi.org/10.4995/ILASS2017.2017.4639OCS1027103

Quantification of mixture composition, liquid-phase fraction and temperature in transcritical sprays

How do fuel and air mix, if a liquid fuel is injected into an environment featuring pressure and temperature that exceed the critical pressure and the critical temperature of the fuel? It is subject of current discussion on whether and if so when, the fuel/air-mixture becomes supercritical or not. We here report experimental data comprising three mixture properties that are relevant for the current debate, all spatially and temporally resolved throughout the spray and injection event: The overall composition of the fuel/air-mixture, the liquid fraction of the fuel/air-mixture, and the temperature of the liquid phase. To this end, we applied Raman spectroscopy and gave special attention to the signature of the Raman OH-band of ethanol, which we used as fuel. Its signature is connected to the development of a hydrogen bonded network between the ethanol molecules and thus extremely sensitive to thermodynamic state and temperature. Measurements were carried out in a high-pressure, high-temperature combustion vessel in a pressure range of 3−8 MPa and a temperature range of 573−923 K. For the highest set temperature we found ethanol in liquid-like mixtures that exceeded the mixture critical temperature. This is an indication of the existence of a single-phase mixing path

Mixture formation of OME3−5 and 1-Octanol in comparison with diesel-like Dodecane under ECN Spray A conditions

In order to be able to use the full potential of regenerative fuels, a comprehensive characterization is necessary to identify the differences between conventional fuels and regenerative fuels. In the current work, we compare OME3−5 and 1-Octanol with diesel-like Dodecane in terms of mixture formation under ECN Spray A conditions for single and multi-injection. To determine the mixtures, i.e., the mass distribution and the resulting air-fuel equivalence ratio, Naber and Siebers’ model as well as Musculus and Kattke’s model are used, which are based on experimental data. For this work, the mass flow rates and also the liquid and gaseous penetration depths of the fuel spray are measured. Results show that the mass ratios for the quasi-steady state of a single main injection for all three fuels are nearly the same, whereas the air-fuel equivalence ratios are very different. In addition, multiple injections are used to show that the fuel influences the opening and closing behavior of the injector. In the transient case of multiple injections, completely different mixtures result. In summary, it can be stated that OME3−5 and also 1-Octanol show a clearly different physio-chemical behavior from Dodecane and cannot simply be used as a drop-in fuel. Therefore, a simple exchange is not possible without major adaptations

Flashboiling-induced targeting changes in gasoline direct injection sprays

By definition, flashboiling is referred to as superheated injections. The sudden occurrence of boiling inside the fuel can change the spray structure dramatically. Up to 99% of all injection processes during the New European Driving Cycle and 95% during ‘Real Driving Emissions’ tests are, with respect to mid-range cars, in a state of thermodynamic non-equilibrium below the specific vapor pressure of gasoline. Considering this fact, the scientific question is not the appearance of flashboiling during the operation of stoichiometric homogeneous charge direct injection gasoline engines but the intensity of occurring spray processes and their influence on nominal spray designs. As a consequence of induced targeting changes, the positive influence of flashboiling on the droplet size distribution and the penetration depth can be counteracted. As main driving factors for targeting changes, jet-to-jet interactions can be identified. By applying appropriate nozzle design features, the potential of flashboiling can be exploited and the targeting changes of the nominal spray designs, considered negatively, are avoided mostly. This work focuses on flashboiling-induced targeting changes, the so-called phenomenon of “spray collapse”: its root cause, development and avoidance