Engine torque may be increased in response to a change in a requested or desired engine torque. Engine torque may be increased via increasing an amount of air and fuel supplied to the engine, at least up to a condition where the engine lacks capacity to induct additional air into engine cylinders. The amount of fuel supplied to the engine may be increased as the amount of air inducted to the engine increases such that the engine operates near stoichiometric conditions. However, there may be conditions where the amount of air inducted to engine cylinders is less than desired. For example, if the engine is supplied gaseous fuel, the gaseous fuel may displace some air in the cylinder, thereby limiting the amount of torque the engine may produce. Consequently, a desired engine torque response may not be provided.
The inventor herein has recognized the above-mentioned disadvantages and has developed an engine operating method, comprising: directly injecting a gaseous fuel to an engine in response to a pressure of gaseous fuel stored in a fuel tank exceeding a threshold level; and increasing an idle speed of the engine and injecting the gaseous fuel to an engine air intake in response to the amount of gaseous fuel stored in the fuel tank being less than the threshold level.
By increasing idle speed of an engine in response to a pressure of fuel stored in a fuel tank, it may be possible to improve an engine's torque response. For example, if a gaseous fuel is directly injected to engine cylinders, the engine may respond quickly to an increase in desired engine torque. However, if the engine transitions to injecting the gaseous fuel via engine intake injection (e.g., injecting fuel to an engine intake manifold or intake ports) when higher pressure gaseous fuel is not available from the gaseous fuel storage tank, engine output torque at engine idle may not respond as quickly as is desired. The engine torque response at lower engine speeds may be dampened since the engine may generate less torque at lower engine speeds because a portion of cylinder volume may be displaced by fuel. However, if engine idle speed is increased, engine power output may increase more rapidly in a short period of time since more combustion events occur for each second of engine operation. Thus, performance of an engine having engine intake injection may be improved so that vehicle acceleration may be more consistent between direct injection and engine intake injection modes.
The present description may provide several advantages. In particular, the approach may reduce improve engine torque response. Further, the approach may make changes between fuel injection modes less noticeable to a driver. Further still, the approach may extend a vehicle's travel range while operating on a gaseous fuel.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.