Injection system for high-volatility fuels (16-Nov-2009)
1) Background of the invention The invention concerns FIE for DME diesel engines. Specifically, the common rail type of FIE with nozzle pressure relief in engine running mode for limitation of DME leakage through closed nozzle. In DME FIE, the general problem is the fuel tank vulnerability to fuel temperature rise due to possibility of overpressure. A more specific problem in this type of FIE is the need to provide additional cooling of the nozzle to prevent fuel evaporation (which can lead to injection instability) when the natural nozzle cooling effect by fuel through-flow is insufficient, for example at low idle. 2) What solutions of the problem are known? Several solutions are known. One is the use of a dedicated cooling system for the fuel. This increases costs and deteriorates reliability. Another is raising backpressure in the nozzle – this increases leakage through closed nozzle. A third known solution is establishing extra recirculating flow through the nozzle to cool it down. This increases internal leakage in the fuel system and heat pick-up by the fuel, ultimately narrowing the ambient temperature range in which the vehicle can be operated. 3) Brief description of the invention The invention is essentially a method of control of CR DME FIE with nozzle pressure relief, the essence of which is that at low engine loads the EMS switches off a number of injectors and simultaneously increases fuelling through the remaining injectors to maintain the torque, thereby achieving increased "natural" cooling effect in the operating nozzles. The injectors that remain in operation are preferably chosen such that the firing sequence of the cylinders remains uniform over the crankangle to reduce NVH. This method of control ensures that the leakage of fuel from injectors back to tank, which is a significant contributor to fuel temperature build-up, is kept to a minimum and is even smaller than in conventional running on all injectors. 4) Advantages over existing solutions Lower cost, better reliability, reduced fuel heat-up and thus higher allowable ambient temperature when vehicle can be operated. 5) See p.2 6) Drawing is attached 7) Yes there should be 8) No
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