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Technical Paper

Injection of Fuel at High Pressure Conditions: LES Study

2011-09-11
2011-24-0041
This paper presents a large eddy simulation study of the liquid spray mixing with hot ambient gas in a constant volume vessel under engine-like conditions with the injection pressure of 1500 bar, ambient density 22.8 kg/m₃, ambient temperature of 900 K and an injector nozzle of 0.09 mm. The simulation results are compared with the experiments carried out by Pickett et al., under similar conditions. Under modern direct injection diesel engine conditions, it has been argued that the liquid core region is small and the droplets after atomization are fine so that the process of spray evaporation and mixing with the air is controlled by the heat and mass transfer between the ambient hot gas and central fuel flow. To examine this hypothesis a simple spray breakup model is tested in the present LES simulation. The simulations are performed using an open source compressible flow solver, in OpenFOAM.
Journal Article

UHC and CO Emissions Sources from a Light-Duty Diesel Engine Undergoing Dilution-Controlled Low-Temperature Combustion

2009-09-13
2009-24-0043
Unburned hydrocarbon (UHC) and carbon monoxide (CO) emission sources are examined in an optical, light-duty diesel engine operating under low load and engine speed, while employing a highly dilute, partially premixed low-temperature combustion (LTC) strategy. The impact of engine load and charge dilution on the UHC and CO sources is also evaluated. The progression of in-cylinder mixing and combustion processes is studied using ultraviolet planar laser-induced fluorescence (UV PLIF) to measure the spatial distributions of liquid- and vapor-phase hydrocarbon. A separate, deep-UV LIF technique is used to examine the clearance volume spatial distribution and composition of late-cycle UHC and CO. Homogeneous reactor simulations, utilizing detailed chemical kinetics and constrained by the measured cylinder pressure, are used to examine the impact of charge dilution and initial stoichiometry on oxidation behavior.
Technical Paper

Influence of Inlet Temperature and Hot Residual Gases on the Performances of a Mini High Speed Glow Plug Engine

2006-11-13
2006-32-0057
Nowadays the power supplying systems have a fundamental importance for all small and portable devices. For low power applications, there are two main ways for producing power: electrochemical batteries and mini engines. Even though in recent years many developments have been carried out in improving the design of batteries, the energy density of 1MJ/kg seems to be an asymptotic value. If the energy source is a hydrocarbon fuel, whose energy density is 46 MJ/kg, with an overall efficiency of only 2.5 % it is possible to surpass the electrochemical batteries. On the other hand, having a mini engine, as energy source, implies three main problems: vibrations, noise and emissions. A light (230 g) model airplane engine with a displacement volume of 4.11 cm3 and a geometrical compression ratio of 13.91 has been studied. The work carried out in this paper can be divided basically in three parts.
Technical Paper

A Real Time NOx Model for Conventional and Partially Premixed Diesel Combustion

2006-04-03
2006-01-0195
In this paper a fast NOx model is presented which can be used for engine optimization, aftertreatment control or virtual mapping. A cylinder pressure trace is required as input data. High calculation speed is obtained by using table interpolation to calculate equilibrium temperatures and species concentrations. Test data from a single-cylinder engine and from a complete six-cylinder engine have been used for calibration and validation of the model. The model produces results of good agreement with emission measurements using approximately 50 combustion product zones and a calculation time of one second per engine cycle. Different compression ratios, EGR rates, injection timing, inlet pressures etc. were used in the validation tests.
Technical Paper

Start of Injection Strategies for HCCI-combustion

2004-10-25
2004-01-2990
Homogeneous Charge Compression Ignition (HCCI) has a great potential for low NOx emissions but problems with emissions of unburned hydrocarbons (HC). One way of reducing the HC is to use direct injection. The purpose of this paper is to present experimental data on the trade off between NOx and HC. Injection timing, injection pressure and nozzle configuration all effect homogeneity of the mixture and thus the NOx and HC emissions. The engine studied is a single cylinder version of a Scania D12 that represents a modern heavy-duty truck size engine. A common rail (CR) system has been used to control injection pressure and timing. The combustion using injectors with different nozzle hole diameters and spray angle, both colliding and non-colliding, has been studied. The NOx emission level changes with start of injection (SOI) and the levels are low for early injection timing, increasing with retarded SOI. Different injectors produce different NOx levels.
Technical Paper

An Air Hybrid for High Power Absorption and Discharge

2005-05-11
2005-01-2137
An air hybrid is a vehicle with an ICE modified to also work as an air compressor and air motor. The engine is connected to two air reservoirs, normally the atmosphere and a high pressure tank. The main benefit of such a system is the possibility to make use of the kinetic energy of the vehicle otherwise lost when braking. The main difference between the air hybrid developed in this paper and earlier air hybrid concepts is the introduction of a pressure tank that substitutes the atmosphere as supplier of low air pressure. By this modification, a very high torque can be achieved in compressor mode as well as in air motor mode. A model of an air hybrid with two air tanks was created using the engine simulation code GT-Power. The results from the simulations were combined with a driving cycle to estimate the reduction in fuel consumption.
Technical Paper

Particle Image Velocimetry Flow Measurements and Heat-Release Analysis in a Cross-Flow Cylinder Head

2002-10-21
2002-01-2840
A specially designed cylinder head, enabling unthrottled operation with a standard cam-phasing mechanism, was tested in an optical single-cylinder engine. The in-cylinder flow was measured with particle image velocimetry (PIV) and the results were compared with heat release and emission measurements. The article also discusses effects of residual gas and effective compression ratio on heat-release and emissions. The special design of the cylinder head, with one inlet and one exhaust valve per camshaft, made it possible to operate the engine unthrottled at part load. Cam phasing led to late inlet valve closing, but also to increased valve overlap. The exhaust valve closing was late in the intake stroke, resulting in high amounts of residual gases. Two different camshafts were used with late inlet valve closing. One of the camshafts had shorter valve open duration on the phased exhaust cam lobe.
Technical Paper

A Simple Approach to Studying the Relation between Fuel Rate Heat Release Rate and NO Formation in Diesel Engines

1999-10-25
1999-01-3548
Modern diesel engine injection systems are largely computer controlled. This opens the door for tailoring the fuel rate. Rate shaping in combination with increased injection pressure and nozzle design will play an important role in the efforts to maintain the superiority of the diesel engine in terms of fuel economy while meeting future demands on emissions. This approach to studying the potential of rate shaping in order to reduce NO formation is based on three sub-models. The first model calculates the fuel rate by using standard expressions for calculating the areas of the dimensioning flow paths in the nozzle and the corresponding discharge coefficients. In the second sub-model the heat release rate is described as a function of available fuel energy, i.e. fuel mass, in the cylinder. The third submodel is the multizone combustion model that calculates NO for a given heat release rate under assumed air /fuel ratios.
Technical Paper

Cylinder to Cylinder and Cycle to Cycle Variations in a Six Cylinder Lean Burn Natural Gas Engine

2000-06-19
2000-01-1941
The cylinder to cylinder and cycle to cycle variations were measured in a production type Volvo natural gas engine. Cylinder pressure was measured in all six cylinders. Emission measurements were performed individually after all cylinders, and commonly after the turbocharger. Measurements (ECE R49 13-mode) were performed with different spark gap and two different locations for fuel injection, one before the throttle and one before the turbocharger. Heat-release and lambda calculations show substantial cylinder to cylinder variations, due to lambda variations between the cylinders. The slow burn combustion chamber, with low turbulence, results in high cycle to cycle variations (> 100% COV imep) for some of the load cases.
Technical Paper

Load Control Using Late Intake Valve Closing in a Cross Flow Cylinder Head

2001-09-24
2001-01-3554
A newly developed cross flow cylinder head has been used for comparison between throttled and unthrottled operation using late intake valve closing. Pressure measurements have been used for calculations of indicated load and heat-release. Emission measurements has also been made. A model was used for estimating the amount of residual gases resulting from the different load strategies. Unthrottled operation using late intake valve closing resulted in lower pumping losses, but also in increased amounts of residual gases, using this cylinder head. This is due to the special design, with one intake valve and one exhaust valve per camshaft. Late intake valve closing was achieved by phasing one of the camshafts, resulting in late exhaust valve closing as well. With very late phasing - i.e. low load - the effective compression ratio was reduced. This, in combination with high amount of residual gases, resulted in a very unstable combustion.
Technical Paper

The Effect of Valve Strategy on In-Cylinder Flow and Combustion

1996-02-01
960582
This study is focused on the effect of different valve strategies on the in-cylinder flow and combustion A conventional four-valve pentroof engine was modified to enable optical access to the combustion chamber To get information on the flow, a two-component LDV system was applied The combustion was monitored by the use of cylinder pressure in a one-zone heat release model The results show that the flow in the cylinder with the valves operating in the standard configuration has an expected tumble characteristic In this case the high frequency turbulence is homogeneous and has a peak approximately 20 CAD BTDC With one valve deactivated, the flow shows a swirling pattern The turbulence is then less homogeneous but the level of turbulence is increased When the single inlet valve was phased late against the crankshaft dramatic effects on the flow resulted The late inlet valve opening introduced a low cylinder pressure before the valve opened The high pressure difference across the valve introduced a high-velocity jet into the cylinder Turbulence was increased by a factor of two by this operational mode When two inlet valves were used, a reduction of turbulence resulted from a very late inlet cam phase
Technical Paper

Fluid Flow, Combustion and Efficiency with Early or Late Inlet Valve Closing

1997-10-01
972937
This paper is a study of the effects of valve timing and how it influences the in-cylinder fluid flow, the combustion, and the efficiency of the engine. An engine load of 4.0 bar imepnet was achieved by setting the inlet valve closing time early or late to enable unthrottled operation. Inlet valve deactivation was also used and asymmetrical valve timing, i.e. valve timing with the two inlet valves opening and closing at different times. The valve timing was altered by switching cam lobes between the experiments. The results indicate a longer flame development period but a faster combustion with early inlet valve closing compared to the throttled case. For late inlet valve closing, a variation in the combustion duration results. As expected, the pumping mean effective pressure (PMEP) was greatly reduced with early and late inlet valve closing compared to the throttled case.
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