Experiment layout

The Experiment layout is shown in Figure 3.1a. When the engine starts, the air and the biogas are sucked into the engine. The flow meters, marked by F1 and F2, measure the air and the biogas flow rates, which are controlled by valves at the engine inlets. The engine gets the power by combustion to drive the generator to produce the electricity. The thermocouple at the engine outlet measures waste gas temperature, and followed by the gas analyzer to measure the concentration of CO in waste gas.

Figure 3.1b is the layout of waste heat recovery. The heat exchanger is installed following the exhaust pipe. The waste gases flow into the exchanger and transfer heat to water in a separated pipe. There are four thermocouples established at exchanger inlets and outlets. T1 and T2 measure the temperature of waste gases before and after the heat exchanger. T3 and T4 are for water temperature at inlet and outlet. A flow meter is also set up for measuring water flow rate.

Later, oxygen is added to the engine for oxygen-enriched combustion test, whose layout is shown in Fig. 3.1c. Note that oxygen is mixed with biogas before they are sent to engine. There exist a valve and a flow meter to control and measure oxygen flow rate.

3.1.1 Engine

The original four-stroke diesel engine was operated with diesel fuel,

22

using compression to ignite the fuel. In order to use biogas gas as fuel, the spark ignition system was installed to the engine. In other words, The ignition way was changed into spark ignition instead of comprssion one.

Figure 3.2 shows the refurnished engine and its detailed data can be referred in the following table.

Table 3.1 Engine Technical Data Engine Technical Data

Engine model 8031i06

Diesel 4 stroke - Injection type direct

N° of cylinders 3 in line

Total displacement 2.9 L

Bore x Stroke 104 x 115 mm

Compression ratio 17 : 1

Aspiration natural

Cooling system liquid (water + 50% Paraflu11)

Lube oil specifications ACEA E2-96 MIL-L-2104E

Lube oil consumption ~ 0.3% of fuel consumption

Fuel specifications EN 590

Speed governor mechanical (G2 class)

Engine rotating mass moment of inertia 0.942 kg m²

Dry weight ( standard configuration) ~ 370 kg

23

3.1.2 Air Flow meter (VA-400)

The flow meter at air inlet is insertion type VA-400 flow sensor, whose range varies with the installed pipe diameter. In order to maintain the accuracy stipulated in the data sheets, the sensor must be inserted in the center of a straight pipe section with an undisturbed flow progression. An undisturbed flow progression is achieved if the sections in front of the sensor and behind the sensor are sufficiently long, absolutely straight and without any obstructions such as edges, seams, curves etc. The minimum length ahead the sensor along the pipe should be 10 times of pipe diameter and 5 times behind sensor for the fully developed turbulent flow profile, so the measured flow rate can be accurate enough. Figures 3.3a and 3.3b show the flow meter and its detailed data.

3.1.3 Biogas Flow Meter (TF-4000)

The flow meter at biogas inlet is TF-4000 thermal-mass flow meter.

The measuring object generally is a mixture of 60% of CH₄ and 40% of CO2 for biogas produced in current swine farm. Figure 3.4a and Figure 3.4b show the flow meter and its technical data. Operation principle is as following: Two temperature sensors are put on along the flow path of gas.

One of them is heated by a controlled power supply, and the other one is not heated. The temperature difference between these two sensors should be always kept constant under a fixed mass flow rate. The different mass flow rate will result in different temperature difference. Therefore, it can deduce the mass flow rate of fluid flow by the quantity of power supply to maintain the temperature difference between these two sensors.

24

3.1.4 Thermocouple

A thermocouple is a sensor for measuring temperature. It consists of two dissimilar metals joined together at one end, which can produce a small unique voltage at a given temperature. This voltage is measured and interpreted by a thermometer. Thermocouples are available in different combinations of metals or calibrations. The four most common calibrations are J, K, T and E. Each calibration has a different temperature range and environment.

Type K (Chromel–Alumel) is the most commonly used thermocouple with a sensitivity approximately 41 µV/°C. The voltage of Chromel is positive relative to the one of alumel. It is inexpensive and its temperature is wide, ranging from −200 °C to +1350 °C.

Type J (iron–constantan; −40 ~ +750 °C) has a more restricted range than type K, but with a higher sensitivity about 55 µV/°C. The Curie point of the iron (770 °C) causes an abrupt change in the characteristic, which determines the upper temperature limit.

In this research, K-type thermocouple is used for measuring waste gas temperature and J-type thermocouple is used for water temperature in waste heat recovery. Figures 3.5a and 3.5b show the pictures of these two kinds of thermocouples.

3.1.5 Water Flow Meter (VF-2000)

The VF-2000 Flow Sensor is assembled with a few pieces of components. The sensor body and Shedder bar (vortex generator) are molded as one component. This design approach has reduced the cost as well as the size and weight of the flow meter. Sensor body is made of PPS

25

(Polyphenylene sulfide) and is designed to eliminate deposits. The operating principle of VF-2000 uses a bluff body or shedder bar in the flow to generate a street of vortices downstream. The VF-2000 Flow Sensor measures the flow rate by counting the number of vortices with a piezoelectric sensor. In this research, VF-2000 is used for measuring water flow rate in waste heat recovery. Figure 3.6a and Figure 3.6b show the picture of VF-2000 and its detailed data.

3.1.6 Gas Analyzer (IMR 1400)

Figure 3.7 is IMR 1400, which is used for waste gas component data. It can measure the concentrations of oxygen and carbon monoxide, with which it can deduce the concentration value of carbon dioxide.

3.1.7 Water Pump

The water pump is used to pump cooling water through the heat exchanger. The water is heated by waste gas exhausted from engine.

Figure 3.8 shows the pump and its maximum water flow rate.

3.1.8 Heat Exchanger

The heat exchanger (Fig. 3.9a) is placed at waste gas outlet to heat the water. It has a casting surrounding four sets of copper pipes of water, which each outer wall is welded by many copper fins (see Fig 3.9b) to enhance the heat transfer between the hot waste gas and the cooling water. The void space between the casting and pipes is for the passage of waste gas.

3.1.9 Data Acquisition

Data acquisition system can automatically gather signals from analog

26

and digital measurement sources, such as sensors and devices, under tests.

It uses a combination of PC-based measurement hardware and software to provide a flexible and user-defined measurement system. Usually, the researcher must calibrate sensors and signals before a data acquisition device acquires them. The specifications of these modules of National Instruments are shown in Table 3.2.

Table 3.2 Specifications of the data acquisition modules

Model Signal Type Channels

Max Sampling

Rate

Resolution Signal Input Ranges NI 9203 Current 8 500 k/s 16 bits ±20 mA NI 9211 Thermocouple 4 15 k/s 24 bits ±80 mV

National Instruments, a leader in PC-based data acquisition, offers a complete family of proven data acquisition hardware devices and the powerful and easy-to-use software that can extend to many languages and operating systems. NI CompactDAQ delivers fast and accurate measurements in a small, simple, and affordable system. A CompactDAQ Chassis shown in Figure 3.10a, a product of NI, is adopted because of the following advantages: plug-and-play installation and configuration, AC power supply and USB cable connection, mounting kits available for panel, enclosure, DIN-rail and desktop development, A380 metal construction, more than 5 MS/s streaming analog input per chassis, and Hi-Speed USB-compliant connectivity to PC. Different types of signal process modules are chosen to complete the data acquisition system, including NI 9203 Analog Input Module, NI 9211 Thermocouple

27

Differential Analog Input Module. Both are shown in Figure 3.10b and Figure 3.10c.