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A burn test was conducted to evaluate the propagation of a fire from burning vegetation underneath a vehicle. A 2013 four-door sedan was instrumented with thermocouples throughout the engine compartment, interior, underbody, and trunk as well as a heat flux sensor underneath the vehicle. The vehicle was placed on a bed of straw to simulate a wildland fuel load. The fire was ignited in the vegetation under the engine compartment near the driver-side front wheel. Initially the fire spread outward from the point of origin under the vehicle. As the fire grew, it spread to the engine compartment and travelled through the vegetation outside of the footprint of the vehicle. The fire progressed rearward along the outside of the vehicle while the fire under the engine compartment continued to grow. During the test, the front and rear driver-side doors were opened at t=1.00 min. and t=1.15 min., respectively.

Results from a full-scale vehicle burn test involving a sport utility vehicle illustrated how fire spread throughout the vehicle, how temperature distributions changed over time, and how arcing-through-char does not always occur in a vehicle fire. The fire was initiated on a grommet on the rear portion of the passenger’s side of the engine compartment. Once the temperature near the origin reached approximately 600°C, the rate of fire spread rapidly increased. Over the next 3.5 minutes, the fire spread to all locations within the engine compartment and both front tires. Although certain circuits within the vehicle’s electrical system were energized for the duration of the fire, with the battery located at the rear of the passenger compartment and the ignition switch in the “off” position, no evidence of beaded copper was observed on any of the conductors located in the engine compartment for this test. However, numerous fuses were found to have activated after the fire.

Two full-scale burn tests involving identical side-by-side all-terrain vehicles were conducted to evaluate fire spread, changes in temperature distributions over time, and how burn patterns correlated to the known point of origin of the fires. The fires were initiated by igniting body panels at opposite corners of the vehicles such that in one test the fire propagated downwind and, in the other, it propagated upwind. In both tests, drop-down from the body panels onto the tires resulted in ignition of the tires. This was an important feature of the mechanism of fire spread. Once the tires began to burn, a transition occurred and the rate of fire spread to the remaining portion of the vehicle increased. Although the time between fire initiation and this transition was significantly different in the two tests, the time to spread and to consume the remaining combustibles within each vehicle was relatively consistent, independent of wind direction.

End-of-injection transients have recently been shown to be important for combustion and emissions outcomes in diesel engines. The objective of this work is to develop an understanding of the coupling between end-of-injection transients and the propensity for second-stage ignition in mixtures upstream of the lifted diesel flame, or combustion recession. An injection system capable of varying the end-of-injection transient was developed to study single fuel sprays in a newly commissioned optically-accessible spray chamber under a range of ambient conditions. Simultaneous high-speed optical diagnostics, namely schlieren, OH* chemiluminescence, and broadband luminosity, were used to characterize the spatial and temporal development of combustion recession after the end of injection.

This work contributes to the understanding of physical mechanisms that control flashback, or more appropriately combustion recession, in diesel sprays. A large dataset, comprising many fuels, injection pressures, ambient temperatures, ambient oxygen concentrations, ambient densities, and nozzle diameters is used to explore experimental trends for the behavior of combustion recession. Then, a reduced-order model, capable of modeling non-reacting and reacting conditions, is used to help interpret the experimental trends. Finally, the reduced-order model is used to predict how a controlled ramp-down rate-of-injection can enhance the likelihood of combustion recession for conditions that would not normally exhibit combustion recession. In general, fuel, ambient conditions, and the end-of-injection transient determine the success or failure of combustion recession.