More on GM's new direct injected engines
Both engines use a split pulse injection strategy for cold starts. Part of the fuel is injected at the end of the compression stroke to provide a rich mixture right around the spark plug. The dished top of the pistons helps contain the fuel and warm up the cylinder. After the initial injection pulse burns the rest of the fuel is injected and ignites in a leaner mixture. This helps with cold start and gets the catalytic converter warmed up faster for lower emissions. Once the engine and catalyst warm up, the control reverts back to a more conventional single pulse strategy.
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