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TECHNICAL PAPERS: Internal Combustion Engines

Post-Combustion In-Cylinder Vaporization During Cranking and Startup in a Port-Fuel–Injected Spark Ignition Engine

[+] Author and Article Information
Jim S. Cowart

Mechanical Engineering Department,  U.S. Naval Academy, Annapolis, MD 21402

J. Eng. Gas Turbines Power 128(2), 397-402 (Aug 05, 2005) (6 pages) doi:10.1115/1.2061307 History: Received February 01, 2005; Revised August 05, 2005

During port-fuel–injected (PFI) spark-ignition (SI) engine startup and warm-up fuel accounting continues to be a challenge. Excess fuel must be injected for a near stoichiometric combustion charge. The “extra” fuel that does not contribute to the combustion process may stay in the intake port or as liquid films on the combustion chamber walls. Some of this combustion chamber wall liquid fuel is transported to the engine’s oil sump and some of this liquid fuel escapes combustion and evolves during the expansion and exhaust strokes. Experiments were performed to investigate and quantify this emerging in-cylinder fuel vapor post-combustion cycle by cycle during engine startup. It is believed that this fuel vapor is evaporating from cylinder surfaces and emerging from cylinder crevices. A fast in-cylinder diagnostic, the fast flame ionization detector, was used to measure this behavior. Substantial post-combustion fuel vapor was measured during engine startup. The amount of post-combustion fuel vapor that develops relative to the in-cylinder precombustion fuel charge is on the order of one for cold starting (0 °C) and decreases to 13 for hot starting engine cycles. Fuel accounting suggests that the intake port puddle forms quickly, over the first few engine cranking cycles. Analysis suggests that sufficient charge temperature and crevice oxygen exists to at least partially oxidize the majority of this post-combustion fuel vapor such that engine out hydrocarbons are not excessive.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 3

Raw FFID data from ambient engine start, with two firing cycles and two misfiring cycles

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Figure 10

Second characteristic hot engine start

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Figure 11

Post-combustion fuel vapor mass normalized to its associated precombustion fuel vapor mass over the first 3 s of engine running

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Figure 12

Post-combustion fuel vapor mass normalized to its corresponding injected mass over the first 3 s of engine running

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Figure 13

Heat release model predicted cylinder charge temperature at EVO over the first 3 s of engine running

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Figure 1

Raw in-cylinder FFID voltage signal during an ambient engine start. Thirteen engine cycles are shown.

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Figure 2

First three cycles from Fig. 1 shown in expanded scale

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Figure 7

First 3 s of engine running for the data shown in Fig. 6

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Figure 4

Ambient engine start (20 °C) cycle-by-cycle analysis of pre- and post-combustion fuel vapor mass levels. Injected fuel mass and puddle increment mass are also shown.

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Figure 5

Second characteristic ambient engine start

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Figure 6

Cold engine start (0 °C) cycle-by-cycle analysis of pre- and post-combustion fuel vapor mass levels. Injected fuel mass and puddle increment mass are also shown.

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Figure 8

Second characteristic cold engine start

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Figure 9

Hot engine start (90 °C) cycle-by-cycle analysis of pre- and post-combustion fuel vapor mass levels. Injected fuel mass and puddle increment mass are also shown.

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