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The simulations are supported by the KAUST Supercomputing Laboratory (KSL) and performed on KSL’s Shaheen II supercomputer. For 3-D simulations, Convergent Science provided CONVERGE licenses while for 1-D simulations, Gamma Technologies provided GT-POWER licenses.

Large Eddy Simulations (LES) were performed using a 3D model of a step nozzle injector. The focus has been on modelling injections with pentane, chosen as a representative single component of the high-volatility components in gasoline. The influence of fuel temperature was investigated with comparisons primarily made between 20 deg C and -10 deg C. The test cases provided a description of the in-nozzle cavitating flow and the macroscopic near-nozzle spray jet structure across different cavitation regimes in order to shed light on engine cold-start effects, a phenomenon prevalent in a number of combustion applications, albeit not extensively studied. The results showed that the size and intensity of the cavitation features tend to become suppressed as the temperature of the fuel decreases. The 20 deg C cases (supercavitating regime) depicted a sporadic shedding of vapour nuclei from a continuous cavitation region that extended to the nozzle outlet surface. Collapse-induced wave dynamics in that region caused a transient entrainment of air from the discharge chamber towards the nozzle inlet. The extent of air entrainment appeared noticeably reduced at the coldest temperature of -10 deg C (incipient cavitation regime) due to the shorter length of the cavitation region, which impeded the backflow of air. Temporally averaged data showed that the near-nozzle jet appearance was also affected by the fuel temperature. The -10 deg C case produced a relatively symmetric jet, in contrast to the supercavitating cases that demonstrated an increased opening angle and a concave surface on the side of the step nozzle edge due to the intense cavitation and parallel air entrainment.

The thorough understanding of the effects due to the fuel direct injection process in modern gasoline direct injection engines has become a mandatory task to meet the most demanding regulations in terms of pollutant emissions. Within this context, computational fluid dynamics proves to be a powerful tool to investigate how the in-cylinder spray evolution influences the mixture distribution, the soot formation and the wall impingement. In this work, the authors proposed a comprehensive methodology to simulate the air-fuel mixture formation into a gasoline direct injection engine under multiple operating conditions.At first, a suitable set of spray sub-models, implemented into an open-source code, was tested on the Engine Combustion Network Spray G injector operating into a static vessel chamber. Such configuration was chosen as it represents a typical gasoline multi-hole injector, extensively used in modern gasoline direct injection engines. Afterwards, the Spray G injector was coupled with the Darmstadt optical engine and full-cycle simulations were carried out for three operating points, combining two engine speeds, respectively equal to 800 rpm and 1500 rpm, and two different engine loads, with pressures of 0.95 bar and 0.4 bar in the intake manifold. The case at 800 rpm and 0.95 bar represented the reference condition. By switching to 1500 rpm and 0.95 bar the effect of the piston speed on the in-cylinder flow and spray evolution was analysed, while the reduction of the intake pressure down to 0.4 bar, coupled with the engine speed of 800 rpm, allowed to study the effects of the engine load on spray evolution and mixture fraction formation. Furthermore, comparisons between the engine cases at 0.95 bar and the simulations in vessel allowed to understand the effects exerted by the turbulence generation on the spray morphology.A detailed post-processing was proposed for each condition. For the vessel, axial vapor and liquid penetrations were assessed, along with spray morphology and liquid mass distribution inside the jet. In the engine, quantities such as in-cylinder gas velocities, mixture fraction distribution and charge homogeneity were investigated. The achieved results demonstrated the potential of the computational fluid dynamics as an effective tool for direct-injection, spark ignition engines optimization towards the goals of emissions reduction and increased efficiency.

CO 2 regulations on heavy-duty transport are introduced in essentially all markets within the next decade, in most cases in several phases of increasing stringency. To cope with these mandates, developers of engines and related equipment are aiming to break new ground in the fields of combustion, fuel and hardware technologies. In this work, a novel diesel fuel injector, Delphi's DFI7, is utilized to experimentally investigate and compare the performance of ramped injection rates versus traditional square fueling profiles. The aim is specifically to shift the efficiency and NO x tradeoff to a more favorable position. The design of experiments methodology is used in the tests, along with statistical techniques to analyze the data. Results show that ramped and square rates- A fter optimization of fueling parameters-produce comparable gross indicated efficiencies. Tests were carried out at 1200 and 1425 rpm; for the latter engine speed peak efficiency was attained at considerably lower NO x levels by applying a ramped injection rate. Particulate matter emissions, on the other hand, are generally lower with the use of square profiles. Heat release analysis further reveals that ignition delays in ramped rate operation are quite long, hinting at vastly different spray behavior. The relatively low loads applied in this work only sustain the delays further. Altogether, this causes the potential of the rate shaping capabilities to be underexploited, as direct control over the burn rate is limited with the combustion system used in this work. The results emphasize the need to carefully select ramp slopes for a particular engine geometry, load and speed point, and additional operating parameter settings.

A powerful and efficient turbocharger turbine benefits the engine in many aspects, such as better transient response, lower NOx emissions and better fuel economy. The turbine performance can be further improved by employing secondary flow injection through an injector over the shroud section. A secondary flow injection system can be integrated with a conventional turbine without affecting its original design parameters, including the rotor, volute, and back disk. In this study, a secondary flow injection system has been developed to fit for an asymmetric twin-scroll turbocharger turbine, which was designed for a 6-cylinder heavy-duty diesel engine, aiming at improving the vehicle's performance at 1100 rpm under full-loading conditions. The shape of the flow injector is similar to a single-entry volute but can produce the flow angle in both circumferential and meridional directions when the flow leaves the injector and enters the shroud cavity. The preliminary design consists of ten design parameters, which is able to control circumferential area distributions, exit flow angles, and flow velocities. To investigate the availability of the injection system, a DOE study has been conducted with the creation of 200 different design candidates that cover the entire design space. Each design candidate is evaluated under ten different turbine operating points, which were picked from the engine exhaust pulse at 90 krpm, covering both equal and unequal admission conditions. To evaluate the turbine performance, a full-rotor steady-state simulation has been conducted using the commercial CFD solver ANSYS-CFX 19.2. This study found the injection system does not influence the original turbine matching during the idle operation (zero injection flow). Within the current DOE set-up, the mean turbine torque can be increased by 24.22%, but the improvement of energy-weighted mean turbine efficiency is limited because of the extra cost by introducing additional flow resources. The secondary flow injection system can be regarded as a novel turbocompounding technology, which can be used to increase the engine torque whenever needed. The current study reveals the availability of the novel system and provides a framework for further optimizations.

The authors would like to thank the N.A.C.E. consortium in Tsukuba, Japan for funding and support in terms of experimental setup. The authors would further like to thank the Clean Combustion Research Center at KAUST for support and funding.

In computational fluid dynamic simulations of partially premixed combustion engines it is common to find simplifications of the in cylinder flow conditions in order to save computational cost. One common simplification is to start the simulation at the moment of intake valve closing with an assumed initial flow condition, rather than making a full scavenging simulation. Another common simplification is the periodic sector assumption, limiting all sector cuts of the full cylinder to be identical periodic copies of each other. This work studies how such flow simplifications affect the spray injection and in turn the fuel/air mixing at different injection timings. Focus is put on the stratification of fuel concentration and gas temperature due to interaction of the spray, turbulence and piston geometry. The investigated engine setup consists of a light duty engine with a piston bowl and a five-hole injector. The simulations are performed under non-reacting conditions and utilize the large eddy simulation turbulence model. Both full cylinder mesh and sector mesh simulations are carried out to evaluate the effects of (a) turbulent vs non-turbulent initial conditions at intake valve closing, (b) sector periodicity assumption on the fuel/air mixing in the compression stroke under different PPC injection timings. The unresolved scales are modeled using a transported one-equation sub-grid scale (SGS) turbulence closure and the fuel spray is modelled using Lagrangian particle tracking (LPT). The simulations show that simple laminar initial conditions produce similar levels of mixing as advanced initial conditions with tilted swirl and anisotropic turbulence. The influence of sector periodicity restriction compared to a full cylinder simulation shows slightly increased levels of stratification in terms of temperature and fuel concentration. This difference is shown to depend on turbulent scales at the center of the cylinder inside the piston bowl and was strongest for the advanced injection timings but could also be observed for the earliest injections. (Less)