Balance termico a motores diesel

Engine Balance – The Thinking Has Changed
By Charles G. Ely II, PE and Randy L. Anderson Anderson Consulting, Training & Testing Introduction Balanced combustion on reciprocating engines is important for reliable, emissioncompliant operation. Through the years, a number of engine balance techniques have been developed and utilized. Unfortunately, no clear-cut standard has been established forengine balance methodology or frequency. This paper will discuss the fundamentals of engine balance, describe the history of balancing, and present the most current thinking on proper engine balance technique, equipment, and frequency. Fundamentals of Engine Balance What is engine balance? In gas compression applications, reciprocating engines are designed to proportionately distribute thecompressor and auxiliary loads between the engine’s power cylinders. Unfortunately, a number of factors introduce variability into the cylinder-tocylinder and cycle-to-cycle combustion process. Practical factors affecting cylinder-to-cylinder variability include: Mechanical construction - stroke length, head and piston heights, gasket and ring size, camshaft profile, fuel manifold wave harmonics, etc.Engine and component condition - worn rings, weak lifters, leaking fuel valves, spark plug gap wear, ignition coil degradation, etc. Combustion controls – air/fuel ratio, ignition timing, pcc pressure, engine cooling, etc. To help reduce cylinder-to-cylinder variability, engine operators install fuel balancing valves, hereafter referred to as a fuel gas modulator valves, in the fuel manifold pipingupstream of the cylinder’s fuel injection valve. Using these valves, the operator affects combustion by adjusting the fuel delivery to a given cylinder (thus affecting the cylinder’s air/fuel ratio and burn characteristics). By properly adjusting each cylinder’s fuel gas modulator valve, the combustion in each cylinder can be stabilized and controlled for good engine balance. Why should I balance myengine? There are five reasons to perform an engine balance.

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1. Control peak combustion pressures – assuring safe operation within manufacturer’s specifications 2. Proportionately distribute the horsepower load across the power cylinders – minimizing unbalanced crankshaft torsion forces 3. Reduce misfires and cycle-to-cycle variability - minimizing fuel consumption 4. Minimize excessivestresses on engine components created by high peak firing pressures and detonation – maximizing reliability and availability 5. Control combustion temperatures – stabilizing exhaust emissions Generic Balance Technique The engine balance process can be divided into four simple steps. 1. Direct pressure readings are taken for each power cylinder. 2. The pressure readings are analyzed and compared todetermine which cylinders are firing high and which cylinders are firing low (compared to the average pressure). 3. Using this information, the fuel gas modulator valves are adjusted to make the high pressures lower and/or the low pressures higher (see example below for more details). 4. After the adjustments are made, pressure readings are retaken on all cylinders to assure that the pressuresare balanced within the balance criteria. If the balance is not achieved, Steps 2, 3, and 4 are repeated. Engine Balance Example Imagine that the fuel system of an engine is a line of sprinklers in a sprinkler system (Figure 1). The system has one control valve (the governor) and six adjustable sprinkler heads (modulator valves). The yard needs 10 gallons of water per minute (or so many BTU’s offuel to generate the required horsepower) and the water should be evenly distributed to the grass around each sprinkler head (or the same pressures in every cylinder). To do this, the individual sprinkler heads (or modulator valves) are adjusted. By pinching valves #2 and #5 on sprinklers (modulator valves) the spray will be lower. If the flow through the control valve (governor) stays constant,...