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Technical Paper

Investigation of Combustion Knock Distribution in a Boosted Methane-Gasoline Blended Fueled SI Engine

2018-04-03
2018-01-0215
The characteristics of combustion knock metrics over a number of engine cycles can be an essential reference for knock detection and control in internal combustion engines. In a Spark-Ignition (SI) engine, the stochastic nature of combustion knock has been shown to follow a log-normal distribution. However, this has been derived from experiments done with gasoline only and applicability of log-normal distribution to dual-fuel combustion knock has not been explored. To evaluate the effectiveness and accuracy of log-normal distributed knock model for methane-gasoline blended fuel, a sweep of methane-gasoline blend ratio was conducted at two different engine speeds. Experimental investigation was conducted on a single cylinder prototype SI engine equipped with two fuel systems: a direct injection (DI) system for gasoline and a port fuel injection (PFI) system for methane.
Technical Paper

Investigation and Optimization of CAM actuation of an Over-Expanded Atkinson Cycle Spark-Ignited Engine

2019-04-02
2019-01-0250
An over-expanded engine was investigated via engine simulation in this work with a design constrained Atkinson mechanically actuated cycle mechanism. A conventional 4-stroke spark-ignited turbo-charged engine with a compression ratio of 9.2 and peak BMEP of 22 bar was selected as the baseline. With geometry and design constraints including bore, stroke, compression ratio, clearance volumes at TDC firing and gas exchange, and packaging, two over-expanded engine mechanisms with stroke ratios of 1.3 and 1.5 were designed. Starting with a validated 1D engine simulation model which included calibration of the in-cylinder heat transfer model, SI turbulent combustion model, and combustion knock model, several investigations of the two Atkinson variants including cam optimization were studied. This included investigation of the effects of offset piston TDC locations and different durations of the 4-strokes due to the mechanism.
Technical Paper

Influence of Elevated Injector Temperature on the Spray Characteristics of GDI Sprays

2019-04-02
2019-01-0268
When fuel at elevated temperatures is injected into an ambient environment at a pressure lower than the saturation pressure of the fuel, the fuel vaporizes in the nozzle and/or immediately upon exiting the nozzle; that is, it undergoes flash boiling. It is characterized by a two-phase flow regime co-located with primary breakup, which significantly affects the spray characteristics. Under flash boiling conditions, the near nozzle spray angle increases, which can lead to shorter penetration because of increased entrainment. In a multi-hole injector this can cause other impacts downstream resulting from the increased plume to plume interactions. To study the effect of injector temperature and injection pressure with real fuels, an experimental investigation of the spray characteristics of a summer grade gasoline fuel with 10% ethanol (E10) was conducted in an optically accessible constant volume spray vessel.
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