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Journal Article

Insights into Cold-Start DISI Combustion in an Optical Engine Operating at −7°C

2013-04-08
2013-01-1309
Particulate Matter (PM) emissions reduction is an imminent challenge for Direct Injection Spark Ignition (DISI) engine designers due to the introduction of Particulate Number (PN) standards in the proposed Euro 6 emissions legislation aimed at delivering the next phase of air quality improvements. An understanding of how the formation of combustion-derived nanoparticulates in engines is affected by the engine operating temperature is important for air quality improvement and will influence future engine design and control strategies. This investigation has examined the effect on combustion and PM formation when reducing the engine operating temperature to -7°C. A DISI single-cylinder optical research engine was modified to simulate a range of operating temperatures down to the proposed -7°C.
Technical Paper

Effects of Injection Timing on Liquid-Phase Fuel Distributions in a Centrally-Injected Four-Valve Direct-Injection Spark-Ignition Engine

1998-10-19
982699
An experimental study was carried out to investigate the effects of fuel injection timing on the spatial and temporal development of injected fuel sprays within a firing direct-injection spark-ignition (DISI) engine. It was found that the structure of the injected fuel sprays varied significantly with the timing of the injection event. During the induction stroke and the early part of the compression stroke, the development of the injected fuel sprays was shown to be controlled by the state of the intake and intake-generated gas flows at the start of injection (SOI).The relative influence of these two flow regimes on the injected fuel sprays during this period was also observed to change with injection timing, directly affecting tip penetration, spray/wall impingement and air-fuel mixing. Later in the compression stroke, the results show the development of the injected fuel sprays to be dominated by the increased cylinder pressure at SOI.
Technical Paper

Numerical Study of the Effects of Droplet Size Distribution on Fuel Transport and Air-Fuel Mixing in a Gasoline Direct-Injection Engine

2003-10-27
2003-01-3100
Numerical simulations are performed to investigate the effects of droplet size distribution on fuel transport and air-fuel mixing in a gasoline direct-injection (GD-I) engine. The engine grid was generated using the K3PREP grid generator and the simulations were carried out using the KIVA-3V Release 2 code. Three size distribution functions were considered, namely the Chi-squared (χ2) and two Rosin-Rammler functions with dispersion parameter, q of 3.5 and 7.5 (RRq=3.5 and RRq=7.5). A new subroutine, which arranges the fuel droplets into a spherical cloud of droplets, was developed to allow the in-cylinder placement of fuel droplets with different droplet size distribution. Two cases of intake valve timing were considered. Results of the simulation showed droplet size distribution to affect fuel dispersion under the influence of the in-cylinder gas flows.
Technical Paper

Effects of Fuel Injection Pressure in an Optically-Accessed DISI Engine with Side-Mounted Fuel Injector

2001-05-07
2001-01-1975
This paper presents the results of an experimental study into the effects of fuel injection pressure on mixture formation within an optically accessed direct-injection spark-ignition (DISI) engine. Comparison is made between the spray characteristics and in-cylinder fuel distributions due to supply rail pressures of 50 bar and 100 bar subject to part-warm, part-load homogeneous charge operating conditions. A constant fuel mass, corresponding to stoichiometric tune, was maintained for both supply pressures. The injected sprays and their subsequent liquid-phase fuel distributions were visualized using the 2-D laser Mie-scattering technique. The experimental injector (nominally a hollow-cone pressure-swirl design) was seen to produce a dense filled spray structure for both injection pressures under investigation. In both cases, the leading edge velocities of the main spray suggest the direct impingement of liquid fuel on the cylinder walls.
Technical Paper

Effect of Impinging Airflow on the Near Nozzle Characteristics of a Gasoline Spray from a Pressure-Swirl Atomiser

2006-10-16
2006-01-3343
The effects of impinging airflow on the near nozzle characteristics of an inwardly opening, high pressure-swirl atomiser are investigated in an optically-accessed, steady-state flow rig designed to emulate the intake flow of a typical, side-injected, 4-valve gasoline direct-injection combustion system. The results indicate that the impinging airflow has a relatively minor effect on the initial break-up of the fuel spray. However, the secondary break-up of the spray, i.e. the break-up of liquid ligaments, the spatial distribution of droplets within the spray and the location of the spray within the cylinder are significantly affected by the impinging air.
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