Mk Behringer

Characterisation of Flow Structures in a Direct-Injection Spark-Ignition Engine using PIV, LDV and CFD

In-cylinder air flow structures are known to play a major role in mixture preparation and engine operating limits for DISI engines. In this paper PIV was undertaken on in-cylinder flow fields for three different planes of measurement in the intake and compression strokes of a DISI engine for a lowload engine operating condition at 1500 RPM, 0.5 bar inlet plenum pressure (World Wide Mapping Point). One of these planes was vertical, cutting through the centrally located spark plug (tumble plane); the other two planes were horizontal, one close to TDC (10 mm below fire face) and the other one close to mid stroke (50 mm below fire face). Statistical analysis was undertaken on the numbers of cycles needed to determine ensemble average flow-field and turbulent kinetic energy maps with up to 1200 cycles considered. The effect of engine head temperature was also examined by obtaining flow fields using PIV with the engine head coolant held at 20 °C and 80 °C. LDV measurements were also performed and compared to the data obtained by PIV. Finally comparisons were made between the experimental data and results from CFD simulations using two different turbulence models on a grid of 1 million cells.

Insights into stoichiometric and lean combustion phenomena of gasoline–butanol, gasoline–ethanol, iso-octane–butanol and iso-octane–ethanol blends in an optical SI engine

ABSTRACT Introduction of novel fuels, such as mixtures of ethanol or butanol with hydrocarbons, requires new fundamental understanding of in-cylinder combustion properties in modern direct-injection spark-ignition engines since those can be quite sensitive to fuel properties. Gasoline and its blends with 25% ethanol and butanol at 25% and 16% per volume (the latter equivalent to 10% ethanol blending ratio in terms of oxygen content) were studied in comparison to gasoline, ethanol, and butanol combustion. The same alcohol blending ratios were also employed with iso-octane as the base component for direct comparison. Testing was performed at 1500 RPM with 0.5 bar intake plenum pressure using 20°C or 80°C engine coolant temperature. Thermodynamic parameters were derived using in-cylinder pressure analysis for stoichiometric (ϕ = 1.0) and lean (ϕ = 0.83) fueling over a range of spark advances. Additionally, high speed color and greyscale chemiluminescence imaging was conducted at gasoline’s maximum break torque spark timing, calculating flame growth speeds, flame roundness, and centroid motion. Laminar burning velocity data from the literature and in-cylinder flow measurements from the same engine were used for interpretation. Overall, the analysis showed small differences between gasoline and the blends in general, but showed changes for the pure alcohols with typically much faster flame progression for ethanol and issues with the combustion stability of butanol at low engine temperatures. Alcohol blending, particularly with iso-octane, showed some benefits at lean conditions.

Developing Low Gasoline Particulate Emission Engines through Improved Fuel Delivery

Particulate emissions are of growing concern due to health impacts. Many urban areas around the world currently have particulate matter levels exceeding the World Health Organisation safe limits. Gasoline engines, especially when equipped with direct injection systems, contribute to this pollution. In recognition of this fact European limits on particulate mass and number are being introduced. A number of ways to meet these new stringent limits have been under investigation. The focus of this paper is on particulate emissions reduction through improvements in fuel delivery. This investigation is part of the author’s ongoing particulate research and development that includes optical engine spray and combustion visualisation, CFD method development, engine and vehicle testing with the aim to move particulate emission development upstream in the development process. As part of this work, a spark eroded and a laser drilled injector were fully characterised in a spray vessel under key engine running conditions. Injector nozzle geometries and mass flow data were also measured in great detail. This paper demonstrates using both steady state and transient engine testing that very significant improvements in particulate emissions can be made. Control strategies enabling multiple injections of smaller volumes of fuel per injection are the most promising technology. The MAHLE Flexible ECU (MFE) combined with injector testing allowed early stage development and demonstrated these effects for a number of key engine operating conditions. Most notably it was found that particulate matter emissions could be reduced by 80-90% during the catalyst light off phase. A new approach was developed (MASTER) to simultaneously assess the effects of calibration changes on all emissions to increase testing efficiency and hence get to more optimised solutions faster. This approach was successfully tested on a production engine comparing two injectors achieving 82% reduction in particulate number emissions during the first 200seconds of the NEDC relative to the EU5b baseline. Finally it was found that both fuel properties and injector deposits can have a significant effect on particulate emissions.