CHAPTER-3
3.2 The Experimental Setup
3.2.2 Instrumentations for Measurements
The experimental setup is consisting of a several sensors, transmitters and indicators. These are interfaced with the data acquisition computer (DAC), established for automatic measurement of almost all of the direct and indirect performance parameters. Various measurement systems used to capture the experimental data used in the test rig are, load measurement, fuel injection pressure, cylinder pressure, engine emission and data acquisition system. The elementary measurement parameters are described in the following sections.
Figure 3.2: Variable compression ratio diesel engine.
Figure 3.3: Tilting cylinder block arrangement.
Figure 3.4: Principle of tilting cylinder block assembly.
Figure 3.5: Compression ratio setting.
3.2.2.1 Load Measurement System
The experimental study is conducted at various loads and hence an accurate and reliable load measuring system is an essential requirement. The load measuring system of this experimental test rig consists of a dynamometer of eddy current type, a load cell of strain gauge type and a loading unit. The load is applied by supplying current to the dynamometer using a loading unit. The load applied to the engine is measured by a load cell. The test engine is connected to an eddy current water-cooled dynamometer to provide the load to the engine crankshaft in constant speed mode with the help of electromagnetic force (field current). The dynamometer was calibrated statically by applying a known current. The load sensor, fitted with the dynamometer, sends the load signal
to the digital display in kg. A dynamometer is a device, which is used for measuring force, torque or power produced by an engine. It can also be used to apply load or torque on the engine. The dynamometer used in this study is an eddy current type with a water cooling system. It provides an advantage of quicker rate of load change for rapid load setting. The VCR diesel engine is directly coupled to the eddy current dynamometer with a loading unit in which desired loads up to 12 kg can be applied.
3.2.2.2 Fuel Injection Pressure Measurement System
Fuel injection system admits the fuel into an internal combustion engine. Fuel injection pressure (also called as fuel inline pressure) is the pressure at which fuel is injected into the engine cylinder.
In the present experimental study, a Piezo Sensor, (Make PCB Piezotronics), Model HSM111A22, Range 5000 psi (345 bar), is used to record the fuel injection pressure (refer Figure 3.6-a). Its location is indicated as No. 1 in the Figure 3.6(b). Initially the default value of pressure is 200 bar.
The fuel injection pressure can be adjusted to a desired point while the engine runs with or without a range given by the company to examine the performance, combustion characteristics and emission analysis of diesel engine. Fuel injection pressure setting can be done online when engine running. When we rotate the slotted nut to anti clockwise from the default setting the injection pressure decrease whereas clockwise rotation increases injection pressure. During experimentation, it is adjusted approximately for about 188 bar, 210 bar and 224 bar. The injection pressure is changed by adjusting the fuel injector spring tension, which is carried out by tightening or loosening the nut for higher, or lower injection pressures respectively (refer Figure 3.7).
Important setting procedures are: Online diesel injection plot being displayed on the monitor using software, note the injection point displayed on the monitor, and turn the injection point-adjusting nut gradually and note its effect on diesel injection plot. The diesel injection plot shifts horizontally to retard/advance injection point depending upon the direction of rotation. Adjust the nut till desired injection point is obtained.
3.2.2.3 Air and Fuel Flow Measurement
Both air and fuel flow measurement can be performed manually and automatically. Manual airflow measurement is carried out by recording the difference in height of water column in the manometer. It is interconnected across the orifice meter, through which air comes into the engine panel box, before leaving towards the engine manifold. Manual measurement of fuel is executed
by transferring fuel from the tank through the measuring tube for known duration. Airflow transmitter (WIKA Instruments Ltd.) and differential pressure transmitter (Yokogawa Electrical Corporation) that are lined with DAC assess the automatic air and fuel flow amount.
(a) Piezo Sensor (b) Location of fuel pressure sensors Figure 3.6: Fuel pressure sensor: (a) Photographic view of piezosensor; (b) Location of fuel
pressure sensor.
Figure 3.7: The nut adjustment for setting fuel injection pressure (IP).
3.2.2.4 P-θθθθ Measurement
The PCB Piezotronics made two dynamic pressure sensors are fitted on the cylinder head and fuel injector. Both of them has identical specification and capable of distinguish pressure of compression, combustion, explosion, pulsation, cavitations, blast, pneumatic, hydraulic, fluidic
etc. An optical crank angle sensor (Kubler make) is used to measure each degree rotation of crank with TDC pulse.
3.2.2.5 Temperature Measurement
Four PT100 (RTD) temperature sensors measure the inlet and outlet temperatures of engine and calorimeter cooling water flow. The inlet and outlet temperatures of exhaust gas to calorimeter are measured by two K type thermocouples. All of these are interfaced with computer for automatic data recording. The thermocouples used in this work, have a response time more than 0.08 seconds (for the 1500 rpm constant speed engine). Hence, they cannot show the pulsation nature of the exhaust gas in the form of temperature readings and are found almost steady after a certain time (nearly 5 minutes) at a particular load.
3.2.2.6 Cylinder Pressure Measurement System
The cylinder pressure is measured using a Piezo sensor of Make PCB Piezotronics, Model HSM111A22, Range 5000 psi (345 bar), and diaphragm stainless steel and hermetically sealed type, by mounting it on the cylinder head. The piezo sensor is mounted on engine head. Its photographic view is shown Figure 3.6(a), and its location is indicated as No. 2 in the Figure 3.6(b). The piezoelectric transducer produces a charge output, which is proportional to the in- cylinder pressure. This charge output is supplied to a piezo powering unit (Make Cuadra model, AX-104). The piezo sensor consists of a quartz crystal. One end of the sensor is exposed to the cylinder pressure through the diaphragm. As the pressure inside the cylinder increases the crystal is compressed. Since the piezoelectric crystals have a tendency to generate electric charge when deformed, the sensor generates electric charge proportional to the pressure. The charge generated is smaller in magnitude and difficult to measure. Hence a charge amplifier is incorporated in the sensor to produce an output voltage proportional to the charge.
3.2.2.7 Injection Timing Variation Control
The IT of the liquid fuel can be tuned online and updated timing is learnt from the fuel pressure data at ceratin crank angle in the software. It is presumed that engine is running in diesel mode and on-line diesel injection plot is being displayed on the monitor using software. Note the injection point displayed on the monitor. Turn the injection point adjusting nut gradually and note its effect on diesel injection plot (refer Figure 3.8). The diesel injection plot shifts horizontally to
retard/advance injection point depending upon the direction of rotation. Adjust the nut till desired injection point is obtained.The injection point can be varied in the range of 0-25° bTDC. During experimentation it is adjusted approximately for about 19° bTDC ( retard), 23° bTDC ( standard or default) and 27° bTDC.
Figure 3.8: The nut adjustment for setting fuel injection timing (IT).
Figure 3.9: Photographic view of the exhaust gas analyser.