UNIVERSITY OF WISCONSIN - ENGINE RESEARCH CENTER

Combustion Imaging Results:

Select Results:

Images were simultaneously captured with a camera focused on natural luminosity and OH chemiluminescence. Presented here are raw natural luminosity images for DPI and RCCI for the base case. DPI shows more propagation into the methane for the same fraction of heat release. RCCI ignition sites tend to be more irregular and grow faster.

Experimental Setup:

As of June 6, 2018

Optical Investigation of Natural Gas and Derivative Fuels for Use in

Advanced Dual-Fuel Combustion Strategies

K. R. Dahl, D. A. Rothamer, and J. B. Ghandhi Funding Sponsor: Direct-injection Engine Research Consortium

Motivation: Natural gas has seen increased use as fuel in IC engines due to its resistance to auto-ignition, low

carbon number, and low cost. Metal engine studies have investigated natural gas combustion using a variety of strategies. While these studies have provided details on performance, there are still unaddressed questions regarding the combustion propagation mechanisms. Using high-speed imaging in an optical engine, we hope to shed light on the nature of these combustion processes.

Operating Conditions:

Future Work: Current work provided some limited sweeps of some interesting parameters. Expanding the pilot

ratio sweep would be interesting as would looking into the effect of injection timing on combustion processes. Finally, other optical diagnostic techniques, such as PLIF, which can provide more quantitative and spatially resolved information, can be employed to provide further insights into the combustion mechanisms.

Displacement [L] 0.41

Geometric Compression Ratio [-]

14

Bore [mm] 82.0

Stroke [mm] 76.2

Optical engine specifications

Cross Section of Optical Engine

RCCI Injection Pressure Sweep: RCCI

displays more spread out and less consistent ignition sites. This is due to the larger amount of mixing present. Low injection pressure creates less mixing. This is seen by the lack of propagation outside the six ignition sites. As mixing increases in C1 ignition sites are more dispersed, and the whole chamber burns. Further increasing the mixing, in C6, results in uneven and irregular ignition sites. This irregular ignition can also be seen in the delayed heat release rate. Proper selection of injection pressure is important to control mixing levels as the degree of mixing can greatly impact how RCCI burns.

DPI Pilot Ratio Sweep: The six ignition sites clearly

correspond to the pilot injection location. Variations in pilot ratio alter the strength and definition of the ignition sites. As pilot ratio decreases, ignition sites move centrally to become visible inside the aperture earlier when compared to SoC. Additionally, the deviations around the pilot ignition time reduce. The size of the pilot also greatly effects the amount of initial heat release. These effects highlight the importance of the pilot ratio on the control of DPI.

C1 C2/C3 C4/C5 C6/C7 C8

Pilot Ratio Base Low/High Base Base 100%

Equivalence Ratio Base Base Low/High Base N/A

Injection Pressure [bar] 600 600 600 1200/300 600

Ignition maps show the average crank angle at which a region begins burning with respect to start of combustion (SoC). This is done by checking when each pixel first crosses a threshold intensity. The maps show the progression of the combustion event in a single image. Contour lines are 1 CAD apart.

(DPI/RCCI) Low Base High

Pilot Ratio 0.05/0.2 0.1/0.3 0.15/0.4

Equivalence Ratio

0.7/0.4 0.8/0.5 0.9/0.6

Other: A variety of other conditions were run, such as a

mid-load DPI, DPI and RCCI with a 2-hole injector, and spark ignited methane. Presented in the maps on the right are the base cases for 2-hole low-load DPI and low-load SI. 2-hole DPI shows characteristics similar to 6-hole DPI and SI combustion. The ignition sites located at the top and bottom of the image are of a similar size and shape to 6-hole DPI. However, once the combustion propagates away from these site, the speed slows to be more consistent with SI.

Image View

Optics Setup

CA50

2.5°

4°

6.25°

8.75°

-5.5°

-4°

-2.75°

-0.5°

DPI – C1 RCCI – C1

CA10 CA10

CA25

CA50

CA75

CA25

CA75

CA50

Optics Transmission

Diesel Pilot

RCCI