Method for transition between controlled auto-ignition and spark ignition modes in direct fuel injection engines

Abstract

A method is provided for control of transition between combustion modes of a direct-injection engine operable in a homogeneous charge compression ignition (HCCI) mode at lower loads and a spark ignition flame propagation (SI) mode at higher loads. The engine includes a variable valve actuation system including two-step high and low lift valve actuation and separate cam phasing for both intake and exhaust valves. The method includes operating the engine at steady state, with fuel-air-exhaust gas mixtures at predetermined conditions, for each speed and load, and controlling the engine during mode changes between the HCCI mode and the SI mode by switching the exhaust and intake valves between low lift for HCCI operation and high lift for SI operation. High load may be an SI throttled mode with an intermediate unthrottled mode (SI / NTLC} in which transition between HCCI and SI / NTLC modes requires switching only the exhaust valve lift and transition between SI / NTLC and SI throttled modes requires switching only the intake valve lift, with predetermined phase adjustments in the valve timing phasing.

Description

technical field [0001] The present invention relates to a method for robust transition between controlled auto-ignition and spark-ignited flame-propagation combustion in gasoline direct injection engines. Background technique [0002] To improve the thermal efficiency of gasoline internal combustion engines, it is known to use air or recirculated exhaust gas dilution combustion to improve thermal efficiency and reduce NOx emissions. However, there is a limit to which engines can operate with lean mixtures because of misfires and combustion instabilities due to slow combustion. Known methods of extending the lean limit include: 1) increasing mixture instabilities by increasing ignition and fuel preparation; 2) increasing flame speed by introducing charge action and turbulence; and 3) operating under controlled auto-ignition combustion engine. [0003] The controlled auto-ignition process is sometimes referred to as the homogeneous charge compression ignition (HCCI) process....

AI Technical Summary

Problems solved by technology

The high load limit for gasoline direct injection controlled auto-ignition combustion engines is extended by more than 10% by the acceptable maximum rate of pressure rise or magnitude of pressure fluctuations

[0009] Although the above advances have successfully demonstrated controlled auto-ignition capability under steady-state conditions, rapid load changes or transitions can lead to undesirable combustion outcomes

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