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Testing of ducted fuel injection (DFI) in a single-cylinder engine with production-like hardware previously showed that adding a duct structure increased soot emissions at the full load, rated speed operating point [1]. The authors hypothesized that the DFI flame, which travels faster than a conventional diesel combustion (CDC) flame, and has a shorter distance to travel, was being re-entrained into the on-going fuel injection around the lift-off length (LOL), thus reducing air entrainment into the on-going injection. The engine operating condition and the engine combustion chamber geometry were duplicated in a constant pressure vessel. The experimental setup used a 3D piston section combined with a glass fire deck allowing for a comparison between a CDC flame and a DFI flame via high-speed imaging. CH* imaging of the 3D piston profile view clearly confirmed the re-entrainment hypothesis presented in the previous engine work.

Exhaust gas recirculation (EGR) is a proven strategy for the reduction of NOX emissions in spark ignited (SI) engines and compression ignition engines, especially in lean burn conditions where the increase of thermal efficiency is obtained. The dilution level of the mixture with EGR is in a conventional SI engine limited by the increase of combustion instability (CoV IMEP). A possible method to extend the EGR dilution level and ensure stable combustion is the implementation of an active pre-chamber combustion system. The pre-chamber spark ignited (PCSI) engine enables fast and stable combustion of lean mixtures in the main chamber by utilizing high ignition energy of multiple flame jets penetrating from the pre-chamber to the main chamber. In this paper, as an initial research step, a numerical analysis is performed by employing the 0D/1D simulation model, validated with the initial experimental and 3D-CFD results.

It is a well-known fact that HCCI combustion offers the possibility of achieving high efficiency with low emissions, but with the challenges in combustion control and ability to adjust to changing environmental conditions. To resolve the aforementioned challenges, a pre-chamber induced homogeneous charge compression ignition (PC-HCCI) combustion mode was experimentally tested with aim of providing initial operating boundaries in terms of combustion stability and obtaining initial performance results. The single cylinder engine equipped with active pre-chamber and compression ratio (CR) of 17.5 was fueled by gasoline. The initial experiments were performed at the engine speed of 1600 rpm with intake air temperatures varied from 33°C to 100°C to verify the possibility of achieving the PC-HCCI combustion mode and to compare the achieved engine performance and emission results with both PCSI and pure HCCI combustion modes used as reference cases.

A promising strategy for increasing thermal efficiency and decreasing emissions of a spark ignited (SI) internal combustion engine is the application of lean mixtures. The flammability limit of lean mixtures can be increased by using an active pre-chamber containing an injector and a spark plug, resulting in a combustion mode commonly called Turbulent Jet Ignition (TJI). The optimization of the combustion chamber shape and operating parameters for TJI combustion can be a demanding task, since the number of design parameters is significantly increased and is today supported by numerical simulations. In this paper, the process of the development of a numerical framework based on 3D CFD and 1D/0D numerical models that will support the research of the pre-chamber design and optimization of operating parameters will be shown. For 3D CFD modelling the AVL Fire™ code is employed, where the full combustion chamber model with intake and exhaust ports of the experimental engine is prepared.

Ducted fuel injection (DFI) was tested for the first time in a heavy-duty diesel metal engine. It was implemented on a Caterpillar 2.5-liter single-cylinder heavy-duty diesel engine fitted with a common rail fuel system and a Tier 4 final production piston. Engine tests consisted of single-injection timing sweeps at A100 and C100, where rail pressure and exhaust gas recirculation (EGR) were also varied. A 6-hole fuel injector tip with 205 am orifices was used with a 130° spray angle and rail pressures up to 250 MPa. The ducts were 14 mm long, had a 2.5 mm inner diameter, and were placed 3.8 mm away from the orifice exits. The ducts were attached to a base, which in turn was attached to the cylinder head with bolts. Furthermore, alignment of the ducts and their corresponding fuel jets was accomplished.

A multi-year Power System R&D project was initiated with the objective of developing an off-road hybrid heavy-duty concept diesel engine with front end accessory drive-integrated energy storage. This off-road hybrid engine system is expected to deliver 15-20% reduction in fuel consumption over current Tier 4 Final-based diesel engines and consists of a downsized heavy-duty diesel engine containing advanced combustion technologies, capable of elevated peak cylinder pressures and thermal efficiencies, exhaust waste heat recovery via SuperTurbo™ turbocompounding, and hybrid energy recovery through both mechanical (high speed flywheel) and electrical systems. The first year of this project focused on the definition of the hybrid elements using extensive dynamic system simulation over transient work cycles, with hybrid supervisory controls development focusing on energy recovery and transient load assist, in Caterpillar’s DYNASTY™ software environment.

An improved method for studying mixing-controlled compression ignition (MCCI) flame interactions with an engine combustion chamber has been developed. It is implemented in a constant pressure vessel, which contains a portion of a piston and a portion of a cylinder head, where the cylinder head is emulated by a transparent fused silica window. This method allows for vaporizing or combusting fuel jets to be imaged from two orthogonal directions. The piston and cylinder head can be adjusted to emulate in-engine piston positions from top dead center (TDC) to approximately 15 mm away from TDC. The design allows for pistons from engine bore sizes up to approximately 175 mm to be studied, including the ability to simulate injector spray included angles from 120°-180°. In this study, the piston was made as an extruded piston bowl profile, where the length of the extrusion approximated the arc length between two neighboring jets from a 6-hole injector.

Driving cycles are usually defined by vehicle speed as a function of time and they are typically used to estimate fuel consumption and pollutant emissions. Currently, certification driving cycles are mainly used for this purpose. Since they are artificially generated, the resulting estimates and analyzes can generally be biased. In order to address these shortcomings, recent research efforts have been directed towards development of statistically representative synthetic driving cycles derived from recorded real-world data. To this end, this paper focuses on synthesis of multidimensional driving cycles using the Markov chain-based method and particularly on their validation. The synthesis is based on Markov chain of fourth order, where the road slope is accounted, as well. The corresponding transition probability matrix is implemented in the form of a sparse matrix parameterized with a rich set of recorded city bus driving cycles.

Textbook engine thermodynamics predicts that SI (Spark Ignition) engine efficiency η is a function of both the compression ratio CR of the engine and the specific heat ratio γ of the working fluid. In practice the compression ratio of the SI engine is often limited due to “knock”. Knock is in large part the effect of end gases becoming too hot and auto-igniting. Knock results in increase in heat transfer to the walls which negatively affects efficiency. Not to mention damages to the piston. One way to lower the end-gas temperature is to cool the intake gas before inducting it into the combustion chamber. With colder intake gases, higher CR can be deployed, resulting in higher efficiencies. In this regard, we investigated the efficiency of a standard Waukesha CFR engine. The engine is operated in the SI engine mode, and was operated with two differing mixtures at different temperatures.

Ongoing development of a CFD framework for the simulation of primary atomization of a high pressure diesel jet is presented in this work. The numerical model is based on a second order accurate, polyhedral Finite Volume (FV) method implemented in foam-extend-4.1, a community driven fork of the OpenFOAM software. A geometric Volume-of-Fluid (VOF) method isoAdvector is used for interface advection, while the Ghost Fluid Method (GFM) is used to handle the discontinuity of the pressure and the pressure gradient at the interface between the two phases: n-dodecane and air in the combustion chamber. In order to obtain highly resolved interface while minimizing computational time, an Adaptive Grid Refinement (AGR) strategy for arbitrary polyhedral cells is employed in order to refine the parts of the grid near the interface. Dynamic Load Balancing (DLB) is used in order to preserve parallel efficiency during AGR.

Syngas produced from biomass gasification is being increasingly considered as a promising alternative to traditional fuels in Spark-Ignition (SI) Internal Combustion Engines (ICEs). Due to the low energy density and extreme variability in the composition of this gaseous fuel, numerical modeling can give an important contribution to assure stable engine performances. The present work intends to give a contribution in this sense in this sense, by proposing a multi-level set of approaches, characterized by an increasing detail, as a tool aimed at the optimization of energy conversion of non-conventional fuels. At first, a specific characterization of the dependency of the syngas laminar flame speed upon its composition is achieved through an iterative approach pursued in the ANSYS ChemkinTM environment, where validated correlations of the flame speed tuning parameters are obtained in a zero-dimensional framework.

The Society of Automotive Engineers Fatigue Design & Evaluation Committee [SAE FD&E] is actively working on a total life project for weldments, in which the welding residual stress is a key contributor to an accurate assessment of fatigue life. Physics-based welding process simulation and various types of residual stress measurements were pursued to provide a representation of the residual stress field at the failure location in the fatigue samples. A well-controlled and documented robotic welding process was used for all sample fabrications to provide accurate inputs for the welding simulations. One destructive (contour method) residual stress measurement and several non-destructive residual stress measurements-surface X-ray diffraction (XRD), energy dispersive X-ray diffraction (EDXRD), and neutron diffraction (ND)-were performed on the same or similarly welded samples.

Ducted fuel injection (DFI) has been shown to be an effective method to significantly reduce soot formation in mixing controlled compression ignition (MCCI) diesel combustion. This reduction has been demonstrated in both combustion vessels and in an optical engine. The mechanisms driving the soot reduction are to date not fully understood. Optimal duct configurations are also not immediately evident. The objective of this study is to show the effects of two geometric variables, namely distance from fuel injector orifice exit to duct inlet (0.1-6 mm) for a 2x14 mm duct, and duct length variation (8-14 mm) at a given stand-off distance of 0.1 mm. A 138 μm on-axis single-orifice injector operated at 100-250 MPa was used in a heated, continuous flow, constant pressure vessel with optical access.

Single-cylinder engine experiments and computational fluid dynamics (CFD) modeling were used in this study to conduct a comprehensive evaluation of the accuracy of the modeling approach, with a focus on soot emissions. A semi-empirical soot model, the classic two-step Hiroyasu model with Nagle and Strickland-Constable oxidation, was used. A broad range of direct-injected (DI) combustion systems were investigated to assess the predictive accuracy of the soot model as a design tool for modern DI diesel engines. Experiments were conducted on a 2.5 liter single-cylinder engine. Combustion system combinations included three unique piston bowl shapes and seven variants of a common rail fuel injector. The pistons included a baseline “Mexican hat” piston, a reentrant piston, and a non-axisymmetric piston similar to the Volvo WAVE design. The injectors featured six or seven holes and systematically varied included angles from 120 to 150 degrees and hole sizes from 170 to 273 μm.

Ducted fuel injection (DFI) is a developing technology for reducing in-cylinder soot formed during mixing-controlled combustion in diesel compression ignition engines. Fuel injection through a small duct has the effect of extending the lift-off length (LOL) and reducing the equivalence ratio at ignition. In this work, the feasibility of DFI to reduce soot and to enable leaner lifted-flame combustion (LLFC) is investigated for a single diesel jet injected from a 138 μm orifice into engine-like (60-120 bar, 800-950 K) quiescent conditions. High-speed imaging and natural luminosity (NL) measurements of combusting sprays were used to quantify duct effects on jet penetration, ignition delay, LOL, and soot emission in a constant pressure high-temperature-pressure vessel (HTPV). At the highest ambient pressure and temperatures tested, soot luminosity was reduced by as much as 50%.

The paper presents the optimization of injection parameters of directly injected fuel in the dual fuel engine operation. The optimization is performed numerically by using a cycle simulation model of the considered engine. In the cycle simulation model, combustion is simulated by a newly developed quasi-dimensional dual fuel combustion model. The model is based on the modified multi-zone combustion model and the quasi-dimensional combustion model. The modified multi-zone combustion model handles the part of the combustion process that is governed by the mixing-controlled combustion, while the modified quasi-dimensional combustion model handles the part that is governed by the flame propagation through the combustion chamber. The developed dual fuel combustion model features a phenomenological description of spray processes, i.e. the liquid spray break-up, fresh charge entrainment, droplet heat-up, and evaporation processes.

Mandated pollutant emission levels are shifting light-duty vehicles towards hybrid and electric powertrains. Heavy-duty applications, on the other hand, will continue to rely on internal combustion engines for the foreseeable future. Hence there remain clear environmental and economic reasons to further decrease IC engine emissions. Turbocharged diesels are the mainstay prime mover for heavy-duty vehicles and industrial machines, and transient performance is integral to maximizing productivity, while minimizing work cycle fuel consumption and CO2 emissions. 1D engine simulation tools are commonplace for “virtual” performance development, saving time and cost, and enabling product and emissions legislation cycles to be met. A known limitation however, is the predictive capability of the turbocharger turbine sub-model in these tools.

This paper presents a newly developed quasi-dimensional multi-zone dual fuel combustion model, which has been integrated within the commercial engine system simulation framework. Model is based on the modified Multi-Zone Combustion Model and Fractal Combustion Model. Modified Multi-Zone Combustion Model handles the part of the combustion process that is governed by the mixing-controlled combustion, while the modified Fractal Combustion Model handles the part that is governed by the flame propagation through the combustion chamber. The developed quasi-dimensional dual fuel combustion model features phenomenological description of spray processes, i.e. liquid spray break-up, fresh charge entrainment, droplet heat-up and evaporation process. In order to capture the chemical effects on the ignition delay, special ignition delay table has been made.

Fundamental understanding of the sources of fuel-derived Unburned Hydrocarbon (UHC) emissions in heavy duty diesel engines is a key piece of knowledge that impacts engine combustion system development. Current emissions regulations for hydrocarbons can be difficult to meet in-cylinder and thus after treatment technologies such as oxidation catalysts are typically used, which can be costly. In this work, Computational Fluid Dynamics (CFD) simulations are combined with engine experiments in an effort to build an understanding of hydrocarbon sources. In the experiments, the combustion system design was varied through injector style, injector rate shape, combustion chamber geometry, and calibration, to study the impact on UHC emissions from mixing-controlled diesel combustion.

Commonly, the spray process in Direct Injection (DI) diesel engines is modeled with the Euler Lagrangian discrete droplet approach which has limited validity in the dense spray region, close to the injector nozzle hole exit. In the presented research, a new reactive spray modelling method has been developed and used within the 3D RANS CFD framework. The spray process was modelled with the Euler Eulerian multiphase approach, extended to the size-of-classes approach which ensures reliable interphase momentum transfer description. In this approach, both the gas and the discrete phase are considered as continuum, and divided into classes according to the ascending droplet diameter. The combustion process was modelled by taking into account chemical kinetics and by solving general gas phase reaction equations.