Internal combustion engines are well known and widely used throughout the world. Virtually all modern work machines, and many power generation systems depend upon internal combustion engines as either a primary power source, or indirectly to provide electricity for operation. Over the many decades of internal combustion engine development, engineers have devised means for operating such engines in virtually every conceivable environment. While sophisticated control and operating systems allow most modern internal combustion engines to operate under extremes of temperature, inherent sensitivities within the engine hardware can still place limitations on operation, particularly with respect to initiating operation under cold conditions.
In certain fuel injected internal combustion engines, inherent difficulty in accurately controlling the quantities of fuel injected in very small injection events can actually make cold starting easier. In some systems, an inherent uncertain sluggishness exists in admission valve opening and closing during a cold start. As a result, fuel may begin injecting relatively more slowly than actually commanded by the control system. Under cold starting conditions, the initially sluggish start of injection can actually make cold starting easier, as the slower initial rate of injection of cold fuel actually tends to facilitate ignition once autoignition conditions are reached in the cylinder. In certain other systems, for example, some high pressure common rail designs, the start of injection tends to be quite abrupt. By removing the inherent sluggishness in fuel injection, engineers have in some cases made engines more difficult to cold start.
One operating approach that addresses cold starting concerns in a common rail design includes the use of relatively small, closely timed pre-jets of fuel injected in an engine cycle prior to a main injection. The pre-jets can induce an activated condition in an engine cylinder that facilitates ignition of a main shot in situations where main shot ignition would otherwise be difficult or impossible. One challenge to such an approach, however, relates to the tendency for injection of overly large pre-jets to absorb too much heat from the cylinder charge air. In other words, heat absorption by the relatively cold fuel of the pre-jets appears to reduce the temperature of the charge air to a point where ignition of the main injection is undermined. Thus, rather than facilitating cold starts, the use of pre-jets can inhibit, or at least fail to improve, ignition of the main fuel injection, in certain instances.
U.S. Pat. No. 5,231,962 to Osuka et al. is directed to one method and control system for enhancing diesel engine starting ability under certain conditions. Osuka et al. utilize one or more pre-jets of fuel injected prior to a main jet of fuel during an engine cycle. The pre-jet is stated to develop an easily ignitable, activated condition in the cylinder conducive to ignition of the main jet of fuel. While Osuka et al. appear to recognize one approach to addressing starting problems in diesel engines, there is always room for improvement.
The present disclosure is directed to one or more of the problems or shortcomings set forth above.