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Technical Paper

The Effect of Zinc and Other Metal Carboxylates on Nozzle Fouling

A problem for the diesel engine that remains since its invention is injection nozzle hole fouling. More advanced injection systems and more complex fuels, now also including bio-components, have made the problem more intricate. Zinc and biodiesel have often been accused of being a big part of the problem, but is this really the case? In this study, nozzle fouling experiments were performed on a single cylinder engine. The experiments were divided in three parts, the first part studied the influence of zinc neodecanoate concentration on nozzle hole fouling, the second part studied the effect of neodecanoates of zinc, sodium, calcium, copper, and iron on fuel flow loss and in the last part it was examined how RME concentration in zinc neodecanoate contaminated petroleum diesel affected nozzle hole fouling propensity. After completed experiments, the nozzles were cut open and the deposits were analyzed in SEM and with EDX.
Technical Paper

Swirl and Injection Pressure Effect on Post-Oxidation Flow Pattern Evaluated with Combustion Image Velocimetry, CIV, and CFD Simulation

In-cylinder flow pattern has been examined experimentally in a heavy duty optical diesel engine and simulated with CFD code during the combustion and the post-oxidation phase. Mean swirling velocity field and its evolution were extracted from optical tests with combustion image velocimetry (CIV). It is known that the post-oxidation period has great impact on the soot emissions. Lately it has been shown in swirling combustion systems with high injection pressures, that the remaining swirling vortex in the post-oxidation phase deviates strongly from solid body rotation. Solid body rotation can only be assumed to be the case before fuel injection. In the studied cases the tangential velocity is higher in the centre of the piston bowl compared to the outer region of the bowl. The used CIV method is closely related to the PIV technique, but makes it possible to extract flow pattern during combustion at full load in an optical diesel engine.
Technical Paper

Development of a Heavy Duty Nozzle Coking Test

The diesel engine is still one of the most common and most efficient mobile energy converters. Nevertheless, it is troubled by many problems, one of them being nozzle coking. This is not a new problem; however, due to the introduction of more advanced injection systems and a more diverse fuel matrix, including biofuels, the problem has become more complex. The nozzle holes are also much narrower today than when the problem first appeared and are therefore more sensitive to coking. Two CEC sanctioned coking tests exist for diesel engines, but no universally accepted test for heavy duty engines. In this paper, tests have been performed with B10 doped with 1 ppm zinc on a single cylinder engine, based on a heavy duty engine, with the purpose to develop a simple accelerated coking test. To have relevance to real usage, the test was based on real engine load points from a high power Euro V engine calibration. The coking propensity was studied in an engine speed sweep at max load.
Technical Paper

Demonstration of Air-Fuel Ratio Role in One-Stage Turbocompound Diesel Engines

A large portion of fuel energy is wasted through the exhaust of internal combustion engines. Turbocompound can, however, recover part of this wasted heat. The energy recovery depends on the turbine efficiency and mass flow as well as the exhaust gas state and properties such as pressure, temperature and specific heat capacity. The main parameter influencing the turbocompound energy recovery is the exhaust gas pressure which leads to higher pumping loss of the engine and consequently lower engine crankshaft power. Each air-fuel equivalence ratio (λ) gives different engine power, exhaust gas temperature and pressure. Decreasing λ toward 1 in a Diesel engine results in higher exhaust gas temperatures of the engine. λ can be varied by changing the intake air pressure or the amount of injected fuel which changes the available energy into the turbine. Thus, there is a compromise between gross engine power, created pumping power, recovered turbocompound power and consumed compressor power.
Technical Paper

Controlling the Injector Tip Temperature in a Diesel Dual Fuel Engine

Diesel Dual Fuel, DDF, is a concept where a combination of methane and diesel is used in a compression ignited engine, maintaining the high compression ratio of a diesel engine with the resulting benefits in thermal efficiency. Attention has recently been drawn to the fact that the tip of the diesel injector may reach intolerable temperatures. The high injector tip temperatures in the DDF engine are caused by the reduction in diesel flow through the injector. For dual fuel operation, as opposed to diesel, high load does not necessarily imply a high flow of diesel through the injector nozzle. This research investigated the factors causing high injector tip temperatures in a DDF engine and the underlying mechanisms which transfer heat to and from the injector tip. Parameter sweeps of each influential parameter were carried out and evaluated. In addition to this, a simple and useful model was constructed based on the heat balance of the injector tip.
Technical Paper

Optical Study of Swirl during Combustion in a CI Engine with Different Injection Pressures and Swirl Ratios Compared with Calculations

Spray and mixture formation in a compression-ignition engine is of paramount importance in the diesel combustion process. In an engine transient, when the load increases rapidly, the combustion system needs to handle low λ operation without producing high NOx emissions and large amounts of particulate matter. By changing the in-cylinder flow, the emissions and engine efficiency are affected. Optical engine studies were therefore performed on a heavy-duty engine geometry at different fuel injection pressures and inlet airflow characteristics. By applying different inlet port designs and valve seat masking, swirl and tumble were varied. In the engine tests, swirl number was varied from 2.3 to 6.3 and the injection pressure from 500 to 2500 bar. To measure the in-cylinder flow around TDC, particle image velocimetry software was used to evaluate combustion pictures. The pictures were taken in an optical engine using a digital high-speed camera.
Technical Paper

Characterization and Potential of Dual Fuel Combustion in a Modern Diesel Engine

Diesel Dual Fuel, DDF, is a concept which promises the possibility to utilize CNG/biogas in a compression ignition engine maintaining a high compression ratio, made possible by the high knock resistance of methane, and the resulting benefits in thermal efficiency associated with diesel combustion. A series of tests has been carried out on a single-cylinder lab engine, equipped with a modern common rail injection system supplying the diesel fuel and two gas injectors, placed in the intake runners. One feature of port-injected Dual Fuel is that full diesel functionality is maintained, which is of great importance when bringing the dual fuel technology to market. The objective of the study was to characterize and investigate the potential for dual fuel combustion utilizing all degrees of freedom available in a modern diesel engine. Increased diesel pilot proved efficient at reducing NOx emissions at low λ.
Technical Paper

Combustion Modes in a Diesel-CNG Dual Fuel Engine

Diesel Dual Fuel, DDF, is a concept where a combination of methane and diesel is used in a compression ignited engine, maintaining the high compression ratio of a diesel engine with the resulting benefits in thermal efficiency. One benefit of having two fuels on board the vehicle is the additional degree of freedom provided by the ratio between the fuels. This additional degree of freedom enables control of combustion phasing for combustion modes such as Homogenous Charge Compression Ignition, HCCI, and Partly Premixed Compression Ignition, PPCI. These unconventional combustion modes have great potential to limit emissions at light load while maintaining the low pumping losses of the base diesel engine. A series of tests has been carried out on a single cylinder lab engine, equipped with a modern common rail injection system supplying the diesel fuel and two gas injectors, placed in the intake runners.
Technical Paper

Validation of a Simplified Model for Combustion and Emission Formation in Diesel Engines Based on Correlations for Spray Penetration and Dispersion, Gas Entrainment into Sprays and Flame Lift-off

A simplified combustion and emission formation model for diesel engines has been developed in a project where the long term objective is to predict emissions during transient operation. The intended application implies that the final model must be both computationally inexpensive and comprehensive so that it can be used for optimization of engine control variables when coupled to full-engine simulation software. As starting point, the proposed model uses diesel spray correlations established in combustion vessels regarding spray penetration, dispersion, gas entrainment, ignition and flame lift-off. It has been found that with minor adaption, these correlations are valid also for combustion in an engine. By assuming a fully mixing controlled combustion after ignition and by use of simplified emission models, the correlations have been found useful for predicting trends in engine-out emission with low computational cost.
Technical Paper

A Study of In-Cylinder Fuel Spray Formation and its Influence on Exhaust Emissions Using an Optical Diesel Engine

Increasingly stringent emission legislation as well as increased demand on fuel efficiency calls for further research and development in the diesel engine field. Spray formation, evaporation and ignition delay are important factors that influence the combustion and emission formation processes in a diesel engine. Increased understanding of the mixture formation process is valuable in the development of low emission, high efficiency diesel engines. In this paper spray formation and ignition under real engine conditions have been studied in an optical engine capable of running close to full load for a real HD diesel engine. Powerful external lights were used to provide the required light intensity for high speed camera images in the combustion chamber prior to ignition. A specially developed software was used for spray edge detection and tracking. The software provides crank angle resolved spray penetration data.
Journal Article

Transient EGR in a High-Speed DI Diesel Engine for a set of different EGR-routings

EGR has been proven to reduce NOx emissions from diesel engines significantly and is nowadays widely used in production engines. To reach future emission legislation standards, alternative EGR-routings that deliver higher EGR-rates get into the focus of researchers. As the steady-state emissions are reduced more and more, the emission peaks in transient parts of driving cycles gain importance. Therefore it is interesting to analyze the transient behavior of different EGR-routings. In this work, a 1-D simulation is performed in GT-Power for a 1.9 liter passenger car diesel engine equipped with cooled short-route EGR and a variable geometry turbine. For calibration of the simulation, load transients are measured including the measurement of transient EGR-rates using a fast CO2-analyzer and cylinder pressure to obtain heat-release data.
Technical Paper

Stall Development in a Ported Shroud Compressor using PIV Measurements and Large Eddy Simulation

Surge is a phenomenon that limits the operational range of the compressor at low mass flow rates. The objective of this research is to study effective operational range for a ported shroud compressor. The size of the compressor is typical for a turbocharger used on diesel engines. To be able to extend the operational range, the surge characteristics have to be assessed. This is done by performing measurement of the flow at the inlet to the compressor wheel and pressure fluctuations at the inlet and outlet of the compressor housing. Detailed numerical computations of the flow in the entire compressor section under similar operating conditions have also been carried out. The experimental work includes Particle Imaging Velocimetry (PIV) measurements of the instantaneous and mean velocity field at the inlet. At surge, low frequency pulsations are detected that seem to result from back flow already observed in stall.
Technical Paper

Simulation of Airborne Wear Particles from Disc Brakes

During braking, both the rotor and the pads are worn in disc brakes. This wear process generates particles which may become airborne. In passenger car field tests it is difficult to distinguish these particles from others in the surrounding environment. It may therefore be preferable to use laboratory test stands and/or simulation models to study the amount of airborne wear particles generated. This paper discusses the possibility of predicting the number distribution of airborne wear particles generated from the pad to rotor contact in disc brakes by using general purpose finite element software. A simulation methodology is proposed where the particle coefficient is established by testing at material level. This coefficient is then used in numerical wear simulation at component level. The simulated number distribution is compared to experimental measurements at component level.
Technical Paper

Advantages of Fuels with High Resistance to Auto-ignition in Late-injection, Low-temperature, Compression Ignition Combustion

Oxides of nitrogen (NOx) and smoke can be simultaneously reduced in compression ignition engines by getting combustion to occur at low temperatures and by delaying the heat release till after the fuel and air have been sufficiently mixed. One of the ways to obtain such combustion in modern engines using common-rail direct injection is to inject the fuel near top dead centre with high levels of exhaust gas recirculation (EGR) - Nissan MK style combustion. In this work we study the effect of fuel auto-ignition quality, using four fuels ranging from diesel to gasoline, on such combustion at two inlet pressures and different EGR levels. The experiments are done in a 2 litre single-cylinder engine with a compression ratio of 14 at an engine speed of 1200 RPM. The engine can be easily run on gasoline with a single injection near TDC, even though it cannot be run with very early injection, in the HCCI mode.
Technical Paper

Optimized Filtration in Hydraulic Systems

Often the use of fine filters reduces the wear and increases the system reliability. On the other hand, the service life of fine filter elements can be much shorter compared with coarser ones, which of course will result in higher filtration costs. Setting up a comprehensive model for the ideal filtration is a challenge, as many parameters have to be introduced, which are difficult to translate into numerical values. However, many of the parameters can be included into some key factors to be considered at the filtration design, which makes the proposed model very useful.
Technical Paper

Measurement of the Oil Film Thickness Between the Cylinder Liner and the Piston Rings in a Heavy Duty Directly Injected Diesel Engine

An electrical capacitance measuring method has been used to obtain the cylinder liner oil film thicknesses for various speeds and loads in a heavy duty directly injected diesel engine. Interesting facts have been observed: Increased oil film thickness for the top ring distance to wall during idling. A gas pocket appearing between top ring and liner at increasing speeds and loads movement of the piston in the liner when combustion sets in, the motion is not parallel. temperature seems to have little effect on the oil film thickness. A computer model of the top ring showed good conformance with the measurements over the speed and load range, but the calculated oil film thickness is about 3 to 6 times higher.