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This work contributes to the understanding of physical mechanisms that control flashback, or more appropriately combustion recession, in diesel sprays. A large dataset, comprising many fuels, injection pressures, ambient temperatures, ambient oxygen concentrations, ambient densities, and nozzle diameters is used to explore experimental trends for the behavior of combustion recession. Then, a reduced-order model, capable of modeling non-reacting and reacting conditions, is used to help interpret the experimental trends. Finally, the reduced-order model is used to predict how a controlled ramp-down rate-of-injection can enhance the likelihood of combustion recession for conditions that would not normally exhibit combustion recession. In general, fuel, ambient conditions, and the end-of-injection transient determine the success or failure of combustion recession.

With ever-demanding emission legislations in Compression Ignition (CI) engines, new premixed combustion strategies have been developed in recent years seeking both, emissions and performance improvements. Since it has been shown that in-cylinder air flow affects the combustion process, and hence the overall engine performance, the study of swirling structures and its interaction with fuel injection are of great interest. In this regard, possible Turbulent Kinetic Energy (TKE) distribution changes after fuel injection may be a key parameter for achieving performance improvements by reducing in-cylinder heat transfer. Consequently, this paper aims to gain an insight into spray-swirl interaction through the analysis of in-cylinder velocity fields measured by Particle Image Velocimetry (PIV) when PCCI conditions are proposed. Experiments are carried out in a single cylinder optical Diesel engine with bowl-in-piston geometry.

This work investigates the particulates size distribution of reactivity controlled compression ignition combustion, a dual-fuel concept which combines the port fuel injection of low-reactive/gasoline-like fuels with direct injection of highly reactive/diesel-like fuels. The particulates size distributions from 5-250 nm were measured using a scanning mobility particle sizer at six engine speeds, from 950 to 2200 rpm, and 25% engine load. The same procedure was followed for conventional diesel combustion. The study was performed in a single-cylinder engine derived from a stock medium-duty multi-cylinder diesel engine of 15.3:1 compression ratio. The combustion strategy proposed during the tests campaign was limited to accomplish both mechanical and emissions constraints. The results confirms that reactivity controlled compression ignition promotes ultra-low levels of nitrogen oxides and smoke emissions in the points tested.

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.

Gas engines (fuelled with CNG, LNG or Biogas) for generation of power and heat are, to this date, taking up larger shares of the market with respect to diesel engines. In order to meet the limit imposed by the TA-Luft regulations on stationary engines, lean combustion represents a viable solution for achieving lower emissions as well as efficiency levels comparable with diesel engines. Leaner mixtures however affect the combustion stability as the flame propagation velocity and consequently heat release rate are slowed down. As a strategy to deliver higher ignition energy, an active pre-chamber may be used. This work focuses on assessing the performance of a pre-chamber combustion configuration in a stationary heavy-duty engine for power generation, operating at different loads, air-to-fuel ratios and spark timings.

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.

The dense spray region in the near-field of diesel fuel injection remains an enigma. This region is difficult to interrogate with light in the visible range and difficult to model due to the rapid interaction between liquid and gas. In particular, modeling strategies that rely on Lagrangian particle tracking of droplets have struggled in this area. To better represent the strong interaction between phases, Eulerian modeling has proven particularly useful. Models built on the concept of surface area density are advantageous where primary and secondary atomization have not yet produced droplets, but rather form more complicated liquid structures. Surface area density, a more general concept than Lagrangian droplets, naturally represents liquid structures, no matter how complex. These surface area density models, however, have not been directly experimentally validated in the past due to the inability of optical methods to elucidate such a quantity.

The influence of pressure and temperature on some of the important thermodynamic properties of diesel fuels has been assessed for a set of fuels. The study focuses on the experimental determination of the speed of sound, density and compressibility (via the bulk modulus) of these fuels by means of a method that is thoroughly described in this paper. The setup makes use of a common-rail injection system in order to transmit a pressure wave through a high-pressure line and measure the time it takes for the wave to travel a given distance. Measurements have been performed in a wide range of pressures (from atmospheric pressure up to 200 MPa) and temperatures (from 303 to 353 K), in order to generate a fuel properties database for modelers on the field of injection systems for diesel engines to incorporate to their simulations.

In the past few years’ various studies have shown how the application of a highly premixed dual fuel combustion for CI engines leads a strong reduction for both pollutant emissions and fuel consumption. In particular a drastic soot and NOx reduction were achieved. In spite of the most common strategy for dual fueling has been represented by using two different injection systems, various authors are considering the advantages of using a single injection system to directly inject blends in the chamber. In this scenario, a characterization of the behavior of such dual-fuel blend spray became necessary, both in terms of inert and reactive ambient conditions. In this work, a light extinction imaging (LEI) has been performed in order to obtain two-dimensional soot distribution information within a spray flame of different diesel/gasoline commercial fuel blends. All the measurements were conducted in an optically accessible two-stroke engine equipped with a single-hole injector.

In this work a detailed soot model based on stationary flamelets is used to simulate soot emissions of a reactive Diesel spray. In order to represent soot formation and oxidation processes properly, a calibration of the soot reaction rates has to be performed. This model calibration is usually performed on basis of engine out soot measurements. Contrary to this, in this work the soot model is calibrated on local soot concentrations along the spray axis obtained from laser extinction chamber measurements. The measurements are performed with B7 certification Diesel and a series production multihole injector to obtain engine similar boundary conditions. In order to ensure that the flow and mixture field is captured well by the CFD-simulation, the simulated liquid penetration lengths and flame lift-off lengths are compared to chamber measurements.

Recent studies have shown that the use of highly premixed dual fuel combustion reduces pollutant emissions and fuel consumption in CI engines. The most common strategy for dual fueling is to use two injection systems. Port fuel injection for low reactivity fuel and direct injection for high reactivity fuel. This strategy implies some severe shortcomings for its real implementation in passenger cars such as the use of two fuel tanks. In this sense, the use of a single injection system for dual fueling could solve this drawback trying to maintain pollutant and efficiency benefits. Nonetheless, when single injection system is used, the spray characteristics become an essential issue. In this work the fundamental characteristics of dual-fuel sprays with a single injection system under non-evaporating engine-like conditions are presented.

Ever decreasing permitted emission levels and the necessity of more efficient engines demand a better understanding of in-cylinder phenomena. In swirl-supported compression ignition (CI) engines, mean in-cylinder flow structures formed during the intake stroke deeply influence mixture preparation prior to combustion, heat transfer and pollutant oxidation all of which could potentially improve engine performance. Therefore, the ability to characterize these mean flow structures is relevant for achieving performance improvements. CI mean flow structure is mainly described by a precessing vortex. The location of the vortex center is key for the characterization of the flow structure. Consequently, this work aims at evaluating algorithms that allow for the location of the vortex center both, in ensemble-averaged velocity fields and in instantaneous velocity fields.

The dual-fuel combustion mode known as reactivity controlled compression ignition (RCCI) allows an effective control of the combustion process by means of modulating the in-cylinder fuel reactivity depending on the engine operating conditions. This strategy has been found to be able to avoid the NOx-soot trade-off appearing during conventional diesel combustion (CDC), with diesel-like or better thermal efficiency in a great part of the engine map. The role of the low reactivity fuel properties and engine settings over RCCI combustion has been widely investigated in literature, concluding that the direct-injected fuel injection timing is a key parameter for controlling the in-cylinder fuel stratification. From this, it can be inferred that the physical and chemical characteristics of the direct-injected fuel should have also an important role on the RCCI combustion process.

Most studies about common-rail diesel injection consider the fuel flow along the injector as isothermal. This hypothesis is arguable given the small diameter of the orifices along which the fuel flows, together with the expansions that take place across them. These phenomena may provoke variations in the fuel temperature, which in turn modify the fuel properties (i.e. viscosity, density, speed of sound…), thus influencing injector dynamics as well as the fuel atomization and mixing processes. The present investigation accounts for these effects by means of a 1D model for the fuel flow along a common-rail ballistic injector. Local variations of fuel temperature and pressure are considered by the model thanks to the implementation of the adiabatic flow hypothesis.

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.

Focusing on the dual-mode dual-fuel (DMDF) combustion concept, a combined optimization of the piston bowl geometry with the fuel injection strategy was conducted at low, mid, and high loads. By coupling the KIVA-3V code with the enhanced genetic algorithm (GA), a total of 14 parameters including the piston bowl geometric parameters and the injection parameters were optimized with the objective of meeting Euro VI regulations while improving the fuel efficiency. The optimal piston bowl shape coupled with the corresponding injection strategy was summarized and integrated at various loads. Furthermore, the effects of the key geometric parameters were investigated in terms of organizing the in-cylinder flow, influencing the energy distribution, and affecting the emissions. The results indicate that the behavior of the DMDF combustion mode is further enhanced in the aspects of improving the fuel economy and controlling the emissions after the bowl geometry optimization.

Electrification and hybridization of powerplants in the transportation sector is one of the most important changes in the last few decades. Lithium-ion batteries are the main energy storage systems, but despite the maturity of this technology, it has certain constrains compared to traditional internal combustion engines in the day-to-day usage. As the operating conditions of the batteries are pushed to the limits to overcome certain disadvantages relative to other conventional systems like charge and discharge times or vehicle driving range, new concerns and safety limitations must be considered. High power rates and cooling deficiencies can produce excessive operating temperatures within the cells, leading to problems with degradation or even unchain chemical reactions that can end in thermal runaway, one of the most worrying failure modes attaining electric platforms nowadays.

Economy decarbonization will be one of the main goals for the following years. Research efforts are being focused on reducing carbon-based emissions, by increasing the efficiency of the transport power plants while developing new fuel production methods that reduce the environmental footprint of the refinement process. Consequently, the depletion of conventional fuels derived from petroleum with high carbon content, such as gasoline and diesel, motivated the development of propulsive alternatives for the transportation sector. In this paradigm, methane (CH4) fuel appears as a mid-term solution due to its low carbon content, if compared with traditional fuels, and the low CO2 emissions during its production from renewable sources. However, the intrinsic properties of methane compromise the combustion process, subsequently increasing the emission of CO2.

The combination of more strict regulation for pollutant and CO2 emissions and the new testing cycles, covering a wider range of transient conditions, makes very interesting the development of predictive tools for engine design and pre-calibration. This paper describes a new integrated Virtual Engine Model (VEMOD) that has been developed as a standalone tool to simulate new standard testing cycles. The VEMOD is based on a wave-action model that carries out the thermo-and fluid dynamics calculation of the gas in each part of the engine. In the model, the engine is represented by means of 1D ducts, while the volumes, such as cylinders and reservoirs, are considered as 0D elements. Different sub-models are included in the VEMOD to take into account all the relevant phenomena. Thus, the combustion process is calculated by the Apparent Combustion Time (ACT) 1D model, responsible for the prediction of the rate of heat release and NOx formation.

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.