A Novel Low Cost High Frequency Fuel Injection System for Small Engines

Small engines (<19kW) are used in many offroad applications, in both the domestic and industrial markets. The dominant driving force in these markets is cost; therefore the vast majority of these engines still use low cost carburettors to meter the fuel into the intake port. However all these engines are now facing increasingly strict emission targets and hence require new technologies to meet these new regulations, but any new technology must be extremely cost effective to be applicable. The conventional fuel injection solutions used for many years in the automotive market require complex systems including a fuel pump, pressure regulator, and fuel injector coupled to a sophisticated control module and a multitude of sensors. This type of solution is far too complex and expensive for the vast majority of engines in the small engines market, and would cost significantly more than the engine itself. A novel solution to this problem is high-frequency Pulse Count Injection (PCI). This design of fuel injection system has a single injector, shown in figure 1, which works as a simple positive displacement pump with a fixed geometric volume (typically 0.5μL). Each time the injector is energized it will deliver this known quantity of fuel to the engine (Fig. 2,) without the need for a separate fuel pump or regulator. The total amount of fuel required by the engine can therefore be delivered as a number of high frequency pulses each engine cycle. With the pulse injector working at a fixed frequency (over 1kHz) and a fixed pulse width, the fuel requirement for the complete speed/load range of a small displacement engine can be accomplished. Load and speed inputs can be processed very simply, and as a result the electronics and the power required to run such a system can be kept to a minimum. Figure 1. A PCI next to a UK penny (20mm diameter). Figure 2. Spray pattern generated by a prototype PCI