CFR engine

The research conducted in this thesis was performed using a CFR engine from the Laboratory of Internal Combustion Engines and Automotive Technologies in the Ingolstadt University of Applied Sciences (Technische Hochschule Ingolstadt - THI), Germany.

The usage of this engine was possible due to the international cooperation program "AWARE", between Brazil and Germany, involving both the institutions THI and UFSC. The engine which was utilized in this thesis is the model F1/F2 explained in section 6.1

11.3.1. Engine – Measurement devices

The engine is equipped with different measurement devices, which enable the collection of important data, as the pressure history, temperature of the exhaust gas, relation of air-fuel which is been injected in the combustion chamber.

In figure 24, shows how the measurement devices are placed in the engine. “A” is the pressure regulator, “B” is the intake manifold heater, “C” is the fuel injector, “D” is the displacement sensor of the cylinder head, “E” lambda sensor, “F” is the pickup and piezo- pressure sensor, “G” indicates the Spark Plug, “H” is the exhaust valve and “I” the intake valve, “J” is the PXI-system of the National Instruments. “K” is the computer screen, in which is possible to follow in real time the value of measurement data. L is the handle used to vary the cylinder head position. “M” is the knockmeter. “N” is the fuel bottles, used as a tank,

“O” are the water pipes, used in the cooling system, “P” is the exhaust system, “Q” is the cast box, “R” is the pulley used to connect the CFR engine to the eletric motor.

Figure 24 – CFR and its measurements devices

Font: Author 11.3.2. Knockmeter reading limits

Knockmeter is the display shown in figure 24 as letter “M”. The next figure shows in more details this equipment, which is fundamental to obtain the final results of ON of the fuel under test. Basically, as its name suggest, it measures the knock intensity (K.I) of the fuel which is feeding the engine at that moment. The scale is displayed from a value of 0 to 100, as can be seen in figure 25-a. As higher this value, higher is the knock severity in the engine.

Figure 25 - (a) Knockmeter; (b) Detonation meter - front panel

According to ASTM (2004), index number 10.3.20.1, the knockmeter reading limits shall be from 20 to 80, even if the scale is from 0 to 100. The reason is that the knock intensity is a nonlinear characteristic below 20 and the knockmeter has the potential to be nonlinear above 80. The Knockmeter signal cames from the detonation meter.

11.3.3. Detonation meter

According to ASTM (2004), index number 3.1.4, the detonation meter (figure 25-b) is a instrumentation that accepts the electrical signal from the detonation pickup and provides an output signal for the knockmeter display (figure 25-a).

In the detonation meter there are 3 different variables that can be changed to get the value of the knockmeter reading, these are: meter reading, spread and time constant. In short, these variables don‟t have a specific value to be setup, they have to be setup in the beginning of the measurement. They have influences in the response of the knockmeter, like how fast the knockmeter changes its value when the engine is been operated under knock conditions. Basically, these values depends upon the operator of the engine. Spread is defined in the ASTM (2004), index number 3.1.20, as: the sensitivity of the detonation meter expressed in knockmeter division per ON.

11.3.4. Digital counter reading (DCR) and hand crank

ASTM (2004), index number 3.1.3.2, defines the DCR as a numerical indicator of cylinder height. It is an important value that have to be fixed when the engine is being operated to get ON of a fuel under test, it means that, once started the measurements, to evaluate the ON of a fuel, whatever is the fuels feeding the engine (PRF, TRF or the fuel to be measured to determine the ON), the value of DCR have to be determined and kept with the same value while the measurement is realized. It is shown in the figure 26-a.

The value itself which is shown by DCR is a dimensionless value. According to ASTM (2004), DCR changes in a direct proportion to compression ratio (CR), and usually DCR is related to RON.

This dimensionless value shows if the cylinder height of the engine is being reduced or increased. If the value of DCR increases, it means that the cylinder height decreases, thus, the compression reatio increases. If the value of DCR decreases, it means that the cylinder height increases, thus, the compression reatio decreases.

To increase or decrease the compression ratio during the measurements, there is a hand crank, which the operator must use. To increase CR, is just necessary to turn the hand crank to the upper position, and to decrease CR, just turn to the lower position. It is shown in figure 26-b.

Figure 26 - (a) Digital counter reading (DCR); (b) Hand crank to compression ratio.

Font: Author

11.3.5. Measurement data diyplay in real time

The data from the measurement devices are collected by a PXI system and are shown in the in the computer screen (K- in figure 24), by this way, during the measurements is possible to monitor in real time the value given by the sensors and check if parameters, like the intake temperature, intake pressure, are according to the standard ASTM D2699. In appendix A are shown the informations that are displayed on the computer screen.There are two important parameters displayed in real time:Quantil 95 and KLASP , which are related to the knock detection, explained in section 4: Knock detection overview.

The knock intensity value is, through this method, called Quantil 95 (Maximum Amplitude of Pressure Oscillation - MAPO), is measured in bar. This value is taken from the CDF curve, it is the intersection between the value of 95% of the cumulative frequency and the cumulative pressure curve. As an example, for the operating conditions described by Galloni (2012), for a spark angle of -8.6, the intersection results in a value of MAPO equal to 0.56 bar, as can be seen in the figure 27. °CA is the value of the crank angle degree, in which the spark discharge occurs, this value is fixed as 13°CA BTDC, it was also defined in annex

D. The parameter KLASP shows in percentage, how many working cycles have the occurrence of knock phenomena, if in every cycle there is a knock detection, this value is 100%.

Figure 27 - Cumulative density frequency (CDF)

Font: Modified from Galloni (2012).

In this thesis, as a method to determine the ON, was specified that the minimum value of KLASP for every fuel used during the measurement procedure, had to be at least 82%, due the fact that to measure ON the engine have to operate under knock phenomenon occurrence.