Warsaw University of Technology

Transcription

1 Warsaw University of Technology Faculty of Automotive and Construction Machinery Engineering INSTITUTE OF VEHEECLES Laboratory of Combustion Engines Theory Lab work 4 INDICATOR DIAGRAM developed: mgr inż. Mateusz Bednarski 1

2 1.Introduction Indicator diagram is one of the most important ratings for assessing the internal combustion engine. Indicator diagrams indicates, simultaneously, the pressures and the relative position of the piston for a particular engine cylinder. They are taken for every voyage, both in loaded and ballast condition. Diagram is used to: - calculate indicated power of the engine, - determine peak pressures and compression pressures, - evaluate the process of combustion inside the engine, - evaluate scavenging and exhausting conditions. An indicator diagram shall be determined by a set of components: - indicator with combustion pressure sensor and load sensor, - crankshaft position sensor, - recorder. Indicator diagram shows the difference between the theoretical circulation and circulation actual realized in the test engine. These differences may result from: - the engine working medium is exchanged after each cycle, - by chemical reaction decompressed medium has different physical properties than the compressed medium, - due to leakage cylinder piston amount of medium is changed, - heat is not supplied from outside, but obtained either the combustion of the fuel in the cylinder, - the course of the heat supply is not consistent with the assumptions p = constans and V = constans, - occurs incomplete combustion, - compression and decompresion isn t isotropic (at the beginning heat is supplied from warm cylinder surface to medium, next heat is dissipate from exhaust gasses to cylinder surface and cylinder head. In practice, the engine it is known that operation cycle in the same cylinder can vary between each other. This phenomenon is called the uniqueness of consecutive cycles. The essential causes are: - unequal filling of the cylinder fresh charge, - unequal combustion process. There are 2 types of indicator diagrams that can be taken from the engine cylinder to know the condition and performance of the engine: - A graph showing pressure in the combustion chamber from the crank angle opened indicator diagram (fig. 1) - A graph showing pressure in the combustion chamber volume of the cylinder closed indicator diagram (fig. 2) 2

3 Fig. 1. Opened indicator diagram [1] Fig. 2. Closed indicator diagram [1] 3

4 Test facility/engine parameters: Engine displacement: VSS = 4,4 dm3 Numer of cylinder : i = 4 Compression ratio: ε = 19,3 Cylinder bore: D = 105 mm Piston stroke: S = 127 mm Length of connecting rod: l = 223,77 mm Maximum power: NN =60,3 [kw] at 2200 rpm 2. Aim of the exercise Purpose of the exercises is determine indicator diagram based on data obtained from empirical research and analysis of results. 3. Tasks 3.1 Draw a opened indicator diagram 3.2 Draw a closed indicator diagram Angle and volume correlation: 3.3 Determine the average indicated pressure. Average indicated pressure is a constant pressure to perform the same work as the variables pressure in the cylinder. 4

5 Fig. 3. Average indicated pressure at closed indicator diagram [1] indicated work one cylinder volume Indicated work can be determined from indicator diagram. (Fig. 3) Indicated work is the sum of the absolute work of each stroke (for example graphical integration). absolute work at intake stroke, absolute work at compression stroke, absolute work at combustion stroke, absolute work at exhaust stroke. 5

6 3.4 Determine indicated power i number of cylinder t time of indicated work Time in four stroke engine is: n [rpm] engine speed 3.5 Determined mean effective pressure mean effective pressure, effective engine power, engine speed, engine volume, stroke coefficent (for four stroke engine ). 3.6 Determine effective work one cylinder volume or: i number of cylinder, effective power, t time of indicated work (the same as time ). 3.7 Determine mechanical efficiency 6

7 3.8 Determine supplied heat to one cycle G[kg/h] hour fuel consumption, fuel calorific value. 3.9 Determine overall efficiency 3.10 Match theoretical cycle Match a theoretical cycle (for example: Sabathe, Otto, Diesel cycle) and fit it to determined indicator diagram (as fig.4) Fig. 4. Indicator diagram with theoretical cycle [1] 3.11 Describe the indicator diagram On the closed indicator diagram apply: combustion chamber volume, stroke volume, the value of the mean indicated and mean effective pressure, field effective and indicated work, points of the opening and closing of valves and point of initiation of the combustion process Determine and compare the mean effective pressure of real engines Determine the mean effective pressure for 5 arbitrarily selected engines. Results show at table, blow the whistle on, ignition, supercharge, production year, etc. 7

8 4. Comments Each student must make a report containing: - Opened and closed indicator diagram, - task from chapter 3, - conclusions. It requires knowledge of: - indicator diagrams, - theoretical cycles, - Irregularities in Indicator Diagram (for example: early/late ignition, after burning, leaky fuel injector, low compression, or chocked exhaust), - stroke, TDC/BDC point, valve open/close point on indicator diagram. 5. Literature 1. Fudalej-Kostrzewa E.: Wykres indykatorowy silnika spalinowego, Warsaw University of Technology, Benson R.S., Whitehouse N. D.: Internal combustion engines, Pergamon Press, Heywood J.B.: Internal combustion engine fundamentals, McGraw-Hill Publishing Company, Bertrand D.H.: Practical diesel-engine combustion analysis, Warrendale,