System and method for boosted direct injection engine

A method of operating an engine system including at least a combustion chamber, an intake manifold selectively communicating with the combustion chamber via at least an intake valve, an exhaust manifold selectively communicating with the combustion chamber via at least an exhaust valve, and a turbocharger including a compressor operatively coupled to the intake manifold, the method comprising:

• simultaneously holding the intake valve and the exhaust valve at an opened position while operating the compressor to boost intake manifold pressure relative to exhaust manifold pressure;
• after simultaneously holding the intake valve and the exhaust valve at said opened position, closing the intake valve and the exhaust valve;
• after closing the exhaust valve, injecting fuel directly into the combustion chamber in only a single injection during an engine cycle, the single injection forming a mixture in the combustion chamber having a first air-fuel ratio during a first, lower, exhaust temperature operating condition, and a second air-fuel ratio during a second, higher, exhaust temperature operating condition, the second air-fuel ratio being less rich than the first air-fuel ratio;
• and
• providing an ignition spark to the combustion chamber to combust said injected fuel.

A method of operating an engine including a turbocharger operatively coupled between an intake manifold and an exhaust manifold of the engine, wherein the engine includes at least a combustion chamber selectively communicating with the intake manifold via an intake valve and the exhaust manifold via an exhaust valve, the method comprising:

• during a first condition, operating the turbocharger at a first speed;
• during a second condition, operating the turbocharger at a second speed greater than the first speed;
• transitioning the turbocharger between the first speed and the second speed by, during each of a plurality of cycles of the combustion chamber:
• opening an exhaust valve of the combustion chamber;
• while said exhaust valve is opened, opening an intake valve of the combustion chamber to enable air to flow from the intake manifold through the combustion chamber via the intake valve to the exhaust manifold via the exhaust valve;
• after opening said exhaust valve and said intake valve, closing the exhaust valve and the intake valve;
• after closing at least the exhaust valve, injecting fuel directly into the combustion chamber via a direct fuel injector in only a single injection during an engine cycle, the single injection forming a mixture in the combustion chamber;
• selecting a first air-fuel ratio for the mixture during a first, lower, exhaust temperature operating condition;
• selecting a second air-fuel ratio for the mixture during a second, higher, exhaust temperature operating condition, the second air-fuel ratio being less rich than the first air-fuel ratio;
• and
• combusting at least a portion of said injected fuel by initiating an ignition spark within the combustion chamber via a spark plug.