US Patent 10167806 Methods and system for central fuel injection

Methods and systems are provided for adjusting engine operating conditions for reduction of NOx emissions. In one example, immediately after a fuel shut-off event, in response to an oxygen content of an exhaust catalyst being higher than a threshold, manifold charge cooling may be increased by increasing the portion of fuel delivered to the engine via manifold injection relative to the portion to fuel delivered via one or more of port and direct injection. By increasing manifold cooling, NOx production may be reduced.