Development And Investigation Of Diesel-CNG Dual Fuel Engine

Engine is used to burn liquid oil and its products as major fuel. However, as the earth’s available oil reserves decreases at an increasingly higher speed, energy-saving and emission-reduction catches the focal attention of the society. Study of alternative fuel grows to be a blooming subject. Nature gas, one of kinds of clear, steady and rich fuel, is replacing oil’s prior position, leading us to times of gas fuel.Nature gas is a kind of good-antiknock-quality fuel because of its high flash point. Besides, Engine will discharge less exhausted gas when burning nature gas. With characteristics of both gasoline and diesel, nature gas will fit engine well as an alternative fuel. But original engine has to be specially designed and conversed first, so that technologies of nature gas engine show a diversity of practice.The dual fuel engine designed is a conversion of a6210ZLDS turbo-charging diesel engine, keeping original structure unchanged such as diesel system, air system, etc. A new CNG system is added to supply nature gas, whose injection timing and flow are precisely controlled by ECU. The engine finally realizes operating in a mode named "dual-fuel, dual-period". It operates as a diesel at50%rated power and below, while burns diesel and CNG at higher power when diesel works as pilot fuel, igniting combustible mixture in cylinder.The control strategies of ECU are introduced in this article, including the control strategies when engine changes its operating mode, works steadily at dual-fuel mode and suffers from abnormal situation. Control parameters are gained from lots of experiments and determined finally, through which the major performances of the generating unit’s power source are evaluated.Experiment of speed-governing evaluates the performance of engine’s speed-governing, while60-hours continuous operation evaluates the engine’s stability and economical performance.Through evaluation of dual-fuel mode’s combustion, the characteristic "more CNG, higher PMAX" of low speed dual fuel engine is discovered. Meanwhile, PMAX is analyzed together with exhaust temperature. They are found display along the same rule, which verifies the feasibility of ECU’s control strategies who adjusts the uniformity of cylinders’CNG flow by the standard of exhaust temperature.By simulating the gas flow through nature gas injection valve, the flow rate of gas is found linearly correlate with valve stroke. In the simulation the threshold value of valve stroke HMAX is found at3.5mm, which allows no more flow if higher. This job offers reference data which will be of great help to the injection valve’s performance optimization. Combining it with the curve of valve stroke, this article estimates the hourly rate of CNG flowing into the cylinder, which provides a reference for the optimization of ECU’s control strategies.The dual fuel engine developed finally works at rated speed (750r/min), with rated load (500kW), realizing steady operation with diesel at20percents and CNG at80percents. The cost shows an obvious decrease also.