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Growing awareness about CO2 emissions and their environmental implications are leading to an increase in the importance of thermal efficiency as criteria to design internal combustion engines (ICE). Heat transfer to the combustion chamber walls contributes to a decrease in the indicated efficiency. A strategy explored in this study to mitigate this efficiency loss is to promote low swirl conditions in the combustion chamber by using low swirl ratios. A decrease in swirl ratio leads to a reduction in heat transfer, but unfortunately, it can also lead to worsening of combustion development and a decrease in the gross indicated efficiency. Moreover, pumping work plays also an important role due to the effect of reduced intake restriction to generate the swirl motion. Current research evaluates the effect of a dedicated injection strategy to enhance combustion process when low swirl is used.

This paper attempts to assess the benefits of a unique distributed propulsion concept, known as the Multi-Gas Generator Fan (MGGF) system, over conventional turbofan engines on civilian vertical takeoff and landing (VTOL) applications. The MGGF-based system has shown the potential to address the fundamental technical challenge in designing a VTOL aircraft: the significant mismatch between the power requirements at lift-off/hover and cruise. Vehicle-level performance and sizing studies were implemented using the Grumman Design 698 tilt-nacelle V/STOL aircraft as a notional personal air vehicle (PAV), subjected to hypothetical single engine failure (SEF) emergency landing requirements and PAV mission requirements.

SI engines fueled with hydrogen represent a promising powertrain solution to meet the ambitious target of carbon-free emissions at the tailpipe. Therefore, fast and reliable numerical tools can significantly support the automotive industry in the optimization of such technology. In this work, a 1D-3D methodology is presented to simulate in detail the combustion process with minimal computational effort. First, a 1D analysis of the complete engine cycle is carried out on the user-defined powertrain configuration. The purpose is to achieve reliable boundary conditions for the combustion chamber, based on realistic engine parameters. Then, a 3D simulation of the power-cycle is performed to mimic the combustion process. The flow velocity and turbulence distributions are initialized without the need of simulating the gas exchange process, according to a validated technique.

A mean value based sizing and simulation model has been developed for use in the conceptual design and sizing of hydrogen fueled spark-ignition internal combustion engines (HICE) in the aerospace industry, here ‘mean value’ includes mean effective pressure (MEP), mean piston speed, mean specific power, etc. This model is developed since there is currently no such model readily available for this purpose. When sizing the HICE, statistical data and common practice for gasoline internal combustion engines (GICE) are used to obtain preliminary sizes of the HICE, such as total cylinder volume, bore and stroke; to capture the effect of low volumetric efficiency, the preliminary results are adjusted by a volumetric correction factor until the cycle parameters of HICE are reasonable. A non-dimensional combustion model with hydrogen as fuel is incorporated with existing GICE methods. With this combustion model, the high combustion temperature and high combustion pressure are captured.

Fuel film deposits on combustion chamber walls are understood to be the main source of particle emissions in GDI engines under homogenous charge operation. More precisely, the liquid film that remains on the injector tip after the end of injection is a fuel rich zone that undergoes pyrolysis reactions leading to the formation of poly-aromatic hydrocarbons (PAH) known to be the precursors of soot. The physical phenomena accompanying the fuel film deposit, evaporation, and the chemical reactions associated to the injector film are not yet fully understood and require high fidelity CFD simulations and controlled experimental campaigns in optically accessible engines. To this end, a simplified model based on physical principles is developed in this work, which couples an analytical model for liquid film formation and evaporation on the injector tip with a stochastic particle dynamics model for particle formation.

Spray processes, such as primary breakup, play an important role for subsequent combustion processes and emissions formation. Accurate modeling of these spray physics is therefore key to ensure faithful representation of both the global and local characteristics of the spray. However, the governing physical mechanisms underlying primary breakup in fuel sprays are still not known. Several theories have been proposed and incorporated into different engineering models for the primary breakup of fuel sprays, with the most widely employed models following an approach based on aerodynamically-induced breakup, or more recently, based on liquid turbulence-induced breakup. However, a complete validation of these breakup models and theories is lacking since no existing measurements have yielded the joint liquid mass and drop size distribution needed to fully define the spray, especially in the near-nozzle region.

The objective of this paper is to examine ways in which to implement probabilistic design methods in the aircraft engine preliminary design process. Specifically, the focus is on analytically determining the impact of uncertainty in engine component performance on the overall performance of a notional large commercial transport, particularly the impact on design range, fuel burn, and engine weight. The emphasis is twofold: first is to find ways to reduce the impact of this uncertainty through appropriate engine cycle selections, and second is on finding ways to leverage existing design margin to squeeze more performance out of current technology. One of the fundamental results shown herein is that uncertainty in component performance has a significant impact on the overall aircraft performance (it is on the same order of magnitude as the impact of the cycle itself).

The 4th Workshop of the Engine Combustion Network (ECN) was held September 5-6, 2015 in Kyoto, Japan. This manuscript presents a summary of the progress in experiments and modeling among ECN contributors leading to a better understanding of soot formation under the ECN “Spray A” configuration and some parametric variants. Relevant published and unpublished work from prior ECN workshops is reviewed. Experiments measuring soot particle size and morphology, soot volume fraction (fv), and transient soot mass have been conducted at various international institutions providing target data for improvements to computational models. Multiple modeling contributions using both the Reynolds Averaged Navier-Stokes (RANS) Equations approach and the Large-Eddy Simulation (LES) approach have been submitted. Among these, various chemical mechanisms, soot models, and turbulence-chemistry interaction (TCI) methodologies have been considered.

An existing one-dimensional (1D) spray model, which successfully captures inert spray processes, has been extended to enable prediction of ignition delay and lift-off length under reacting conditions. For that purpose, an additional transport equation for the progress variable has been incorporated, which includes detailed chemistry effects by means of a tabulation method based upon an external flamelet solver. The transport equation for the progress variable is solved in a quasi-1D fashion, along presumed mixture fraction trajectories, while the 1D approach is retained for the mixture fraction and axial velocity fields. The paper includes the model development, as well as the validation against Spray A measurements from the Engine Combustion Network. In spite of the simplified approach, the model captures some of the experimental trends of the lift-off length and ignition delay with a quite low computational cost.

The interest in flying cars comes with the question of characterizing aerodynamic loads on shapes that go beyond traditional aircraft shapes. When carried as slung loads under aircraft, vehicles can encounter severe aerodynamic loads, which may also cause them to go into divergent oscillations that can threaten the vehicle and aircraft. Slung loads can encounter the wind at arbitrary attitudes. Flight test certification for every vehicle-aircraft combination is prohibitive. Characterizing the aerodynamic loads with sufficient resolution for use in dynamic simulation, has in the past been extremely arduous. Sharp changes that drive instabilities arise over small ranges of yaw and pitch. With the Continuous Rotation technique developed by our group, aerodynamic load characterization is viable and efficient. With two well-chosen attitude sweeps and appropriate transformations, the entire 6-DOF load map can be obtained, for several rates.

In order to comply with the increasingly restrictive limits of emissions and fuel consumption, researches are focusing on improving the efficiency of combustion engines. In this area, the aging of the injector and its effect on the injection development is not entirely analyzed. In this work, the rate of injection of a diesel injector at different stages of its lifetime is analyzed. To this end, a multi-hole piezoelectric injector was employed, comparing the injection rate measured at the beginning of its lifetime to the rate provided by the injector after aging, maintaining the same boundary conditions in both measurements. Injection pressures up to 200 MPa were used throughout the experiments. The results showed that the steady-state rate of injection was lower after the injector aged. Furthermore, the injector took a longer time to close the needle and end the injection, in comparison with the measurements done at earlier stages of its lifetime.

Hybrid-electric powertrains for passenger vehicles and light trucks are generally being designed with two different configurations described as follows: The Toyota Hybrid System, THS-II, implemented in the 2004 Prius, the Lexus 400-H, and the Ford Hybrid Escape, is a power-split approach involving two electric machines and an internal combustion engine (ICE) mechanically coupled by a three-shaft planetary gear train. The second leading approach is a parallel hybrid-electric powertrain that generally includes a single electric machine and an ICE with a mating multi-ratio transmission. These parallel configurations are further divided as weak parallel and strong parallel. Honda uses a weak parallel powertrain in their Insight and Hybrid Civic. At Georgia Tech a strong (full), split-parallel hybrid powertrain has been implemented in a Ford Explorer. The vehicle is referred to as the Model GT.

Compared to the gasoline engine, the diesel engine has the advantage of being more efficient and hence achieving a reduction of CO₂ levels. Unfortunately, particulate matter (PM) and nitrogen oxides (NOx) emissions from diesel engines are high. To overcome these drawbacks, several new combustion concepts have been developed, including the PCCI (Premixed Charge Compression Ignition) combustion mode. This strategy allows a simultaneous reduction of NOx and soot emissions through the reduction of local combustion temperatures and the enhancement of the fuel/air mixing. In spite of PCCI benefits, the concept is characterized by its high combustion noise levels. Currently, a promising way to improve the PCCI disadvantages is being investigated. It is related with the use of low cetane fuels such as gasoline and diesel-gasoline blends.

A commercially available fuel, E85, a blend of ~85% ethanol and ~15% gasoline, can be a viable substitute for fossil fuels in internal combustion engines in order to achieve a reduction of the greenhouse gas (GHG) emissions. Ethanol is traditionally made of biomass, which makes it a part of the food-feed-fuel competition. New processes that reuse waste products from other industries have recently been developed, making ethanol a renewable and sustainable second-generation fuel. So far, work on E85 has focused on spark ignition (SI) concepts due to high octane rating of this fuel. There is very little research on its application in CI engines. Alcohols are known for low soot particle emissions, which gives them an advantage in the NOx-soot trade-off of the compression ignition (CI) concept.

The Engine Combustion Network (ECN) is a coordinate effort from research partners from all over the world which aims at creating a large experimental database to validate CFD calculations. Two injectors from ECN, namely Spray C and D, have been compared in a constant pressure flow vessel, which enables a field of view of more than 100 mm. Both nozzles have been designed with similar flow metrics, with Spray D having a convergent hole shape and Spray C a cylindrical one, the latter being therefore more prone to cavitation. Although the focus of the study is on reacting conditions, some inert cases have also been measured. High speed schlieren imaging, OH* chemiluminescence visualization and head-on broadband luminosity have been used as combustion diagnostics to evaluate ignition delay, lift off length and reacting tip penetration. Parametric variations include ambient temperature, oxygen content and injection pressure variations.

Visualization of single-hole nozzles into quiescent ambient has been used extensively in the literature to characterize spray mixing and combustion. However in-cylinder flow may have some meaningful impact on the spray evolution. In the present work, visualization of direct diesel injection spray under both non-reacting and reacting operating conditions was conducted in an optically accessible two-stroke engine equipped with a single-hole injector. Two different high-speed imaging techniques, Schlieren and UV-Light Absorption, were applied here to quantify vapor penetration for non-reacting spray. Meanwhile, Mie-scattering was used to measure the liquid length. As for reacting conditions, Schlieren and OH* chemiluminescence were simultaneously applied to obtain the spray tip penetration and flame lift-off length under the same TDC density and temperature. Additionally, PIV was used to characterize in-cylinder flow motion.

Advanced Computational Fluid Dynamics (CFD) modeling of reacting sprays provides access to information not available even applying the most advanced experimental techniques. This is particularly evident if the combustion model handles detailed chemical kinetic models efficiently to describe the fuel auto-ignition and oxidation processes. Complex chemistry also provides the temporal evolution of key species closely related to emissions formation, such as polycyclic aromatic hydrocarbons (PAHs) that are well-known as soot precursors. In this framework, present investigation focuses on the analysis of the so-called Spray-A combustion characteristics using two different flamelet-based combustion models. Both Reynolds-Averaged Navier-Stokes (RANS) and Large-Eddy Simulation (LES) predictions are combined to study not only the averaged spray characteristics, but also the relevance of different realizations in this particular problem.

Engine Combustion Network promotes fundamental investigations on a number of different spray configurations with the goal of providing experimental results under highly controlled conditions for CFD validation. Most of the available experiments up to now have been obtained in spray vessels, which miss some of the interactions governing spray evolution in the combustion chamber of an engine, such as the jet wall interaction and the transient conditions in the combustion chamber. The main aim of the present research is to compare the results obtained with a three-hole, 90 μm injector, known as ECN’s Spray B, in these constant-volume vessels and more recent Heavy-Duty engines with those obtained in a Light Duty Single Cylinder Optical Engine, under inert and reactive conditions, using n-dodecane. In-cylinder conditions during the injection were estimated by means of a 1-D and 0-D model simulation, accounting for heat transfer and in-cylinder mass evolution.

Compressed natural gas (CNG) is an attractive, alternative fuel for spark-ignited (SI), internal combustion (IC) engines due to its high octane rating, and low energy-specific CO2 emissions compared with gasoline. Directly-injected (DI) CNG in SI engines has the potential to dramatically decrease vehicles’ carbon emissions; however, optimization of DI CNG fueling systems requires a thorough understanding of the behavior of CNG jets in an engine environment. This paper therefore presents an experimental and modeling study of DI gaseous jets, using methane as a surrogate for CNG. Experiments are conducted in a non-reacting, constant volume chamber (CVC) using prototype injector hardware at conditions relevant to modern DI engines. The schlieren imaging technique is employed to investigate how the extent of methane jets is impacted by changing thermodynamic conditions in the fuel rail and chamber.

In order to face the new challenges, spark ignition engines are evolving by following some strategies and technologies. Among them, alternative combustion processes based on the dilution of the homogeneous mixture, either with fresh air or with Exhaust Gas Recirculation (EGR), are being explored. In a higher or lower extent, these changes modify in-cylinder thermodynamic conditions during the engine operation (pressure, temperature and gas composition) thus conditioning the spark ignition system requirements that will have to evolve to become more reliable and powerful. In this framework, an experimental study on the effect of the key in-cylinder conditions on the ignition system performance has been carried out in a single-cylinder spark-ignition (SI) research engine. The study includes EGR, lambda and energizing time sweeps to assess the behavior of the engine in different operating conditions.