Annexure G

Details of Programmes other than Conventional degree: Research

Oriented Activity

1)Improvement of Biogas Conversion Kit-By Prof.(Dr.) G.P.Govil

Contents

Sr. No / Page No.
1 / Introduction
2 / Main Objectives
3 / Scientific/Technical basis for Present Development
4 / Selection of Diesel Engine to convert to Biogas-Engine
5 / Development of Governing Mechanism, Air Gas Mixture
and Ignition Mechanism
6 / Experimental Setup
7 / Results and Discussion
8 / Conclusions
9 / Cost Estimates
10 / Entrepreneurship Possibilities emerging from Present Innovation
and Strategy for Promotion
11 / References
12 / Appendices

1.0 Introduction

In order to give a thrust towards sustainable Rural Industrialization, it is essential to develop commercially viable technologies and rural entrepreneurship packages using these technologies to effectively harness locally available, renewable energy resources in the rural area to provide basic utilities for the rural population and to augment the entrepreneurial activity by value addition to agricultural and other RI products.

In this context, effective utilization/recycling of biomass are a much needed intervention. A substantial quantity of wet as well as dry biomass in various forms becomes naturally available in the rural areas. Appropriate technologies for waste-to-energy conversion of this resource will go a long way in improving rural economy, ecology as well as energy self-sufficiency. Recycling of moist biomass such as animal and human excreta, domestic as well as agro-industrial organic waste through biomethanation is a highly cherished objective which will have universal applicability in the rural sector. In fact, this conversion process makes available renewable energy in the form of biogas as well as valuable biomanure in the form of slurry. It improves rural sanitation, promotes the adoption of organic farming and the use of animals more viable economically.

Biogas production technology from various types of raw materials is, by now, well established and biogas plants of various sizes, and designs suited to different raw materials are already operating in large numbers throughout the country through the sustained efforts of MNRE, KVIC and various NGO’s. However, this development during past few decades has been carried out more as a welfare measure by the Govt. rather than a commercially viable entrepreneurship venture for wide spread waste-to-energy conversion. In fact, even in the urban sector, such a conversion is becoming inevitable in context with large dairy clusters, poultry and other animal farms, sewage treatment plants and even in large hotels, hostels, food processing industries etc. where large amount of organic waste is produced and needs to be recycled in an eco-friendly manner.

In order to integrate above-mentioned waste-to-energy conversion with widespread commercial activity, it is important to devise appropriate field-worthy technologies not only for production but also for commercial utilization of biogas at scales suitable for the rural sector.

The first priority in utilization of biogas should, of course, be in providing a clean fuel for domestic cooking. However, to facilitate large scale utilization of biogas, it is essential to have a suitable energy conversion device i.e. an engine to enable efficient conversion of biogas energy into required mechanical/electrical forms. Presently biogas is being used at a limited scale in dual-fuel engines which partially (to the extent of 30-40%) utilize the diesel fuel. Hence a strong need to have a 100% biogas operated engines has been clearly identified. Small, stationary type diesel engines in the power range 5-20 hp are being universally used in rural areas for water pumping, gen-sets as well as for variety of agro-industrial processing applications. Bulk of these engines is D.I., vertical, single cylinder, ‘Kirloskar’ type design engines operating at 1000-1500 rpm. After a careful assessment of the user needs, entrepreneurship possibilities and the current practice, it was established that the development of a simple kit to convert this spectrum of existing diesel engines into biogas/producer gas engines will be highly desirable.

With the spurt in the use of CNG for heavy duty automobiles, the technology for conversion of high power vehicular diesel engines into spark ignition gaseous fuel engines has now come to the market. However, this technology is quite complex and a different strategy for downsizing and simpler technology is needed to carry out the conversion of small horse power rural application stationary diesel engines.

Conversion kits were developed for small range engines in the range of 3kVA to 7.5 kVA. Diesel engines converted to 100% biogas engines have been installed at number of places and working well. These converted engines did not have speed control mechanism. In some engines mechanical governing system was used but it was not satisfactory. Need was felt to prepare the kit for large engines to cater to the need of goshalas, vegetable markets , fish markets or a cluster of village in the range of 5KVA-20 KVA with suitable governing mechanism.

This work reports the development and field-assessment of 15 kVA biogas generator with conversion kit for rural application.

2.0 Main Objectives

In the light of the above mentioned need, following objectives were kept in mind for developing a suitable conversion kit;

  1. The conversion kit should be a low cost, rugged and user friendly device.
  2. As far as possible, efforts should be made to use standard components, easily available in the automotive engine components market.
  3. Development of governing mechanism
  4. Development of electronic spark ignition mechanism
  5. Development of gas Carburetor i.e Air/Gas mixture

3.0Scientific/Technical basis for Present Development

The scientific principles and the resulting technology involved in the development of the present kit can be understood as follows.

A diesel engine operates on the principle of compression ignition of the diesel fuel. It has relatively higher compression ratio (around 15-22) and a heterogeneous mode of combustion. This mode of ignition is suited only for less volatile liquid fuels with low auto-ignition temperatures. It also uses a fuel injection system which injects the liquid fuel into the engine cylinder at very high pressure towards the end of compression stroke. For gaseous fuels, it is essential to use the spark ignition (S.I.) mode, premix combustion, in which case the air and fuel are homogeneously mixed in an appropriate ratio and then inducted into the engine cylinder. Towards the end of compression, a spark is applied to initiate the ignition of the compressed charge. These engines also need throttling of air-fuel mixture to control the power output.

Normal Spark Ignition Engines which use gasoline fuel are restricted in compression ratio (8-10) because of knocking condition. However, in the case of biogas which contains methane as the fuel element, the auto-ignition temperature is quite high and much higher compression ratio can be used, which leads to improved efficiency. The conversion of a diesel engine into an equivalent spark ignition engine is done the following modifications/retrofitting.

a)Removal of the fuel injection system (fuel pump and the injector)

b)Incorporation of a suitable spark plug in place of the injector by appropriate modification in the injector hole.

c)Modification in the engine intake system incorporating suitable mechanism for air-fuel mixing and control i.e. a gas carburetor system.

d)Retrofitting with cam shaft/crank shaft a specially designed ignition system.

e)Modification in the combustion chamber/compression ratio etc. (if needed)

The overall arrangement of the conversion kit is shown in the schematic layout in Figure 1.

4.0 Selection of Diesel Engine to convert to Biogas-Engine

The main suppliers of diesel engines for generators or for automotive operation in the field are Cummins, TATA & Ashok Leyland. They manufacture the large diesel engine/CNG engine for automotive purposes. A typical automotive engine runs on 3200 rpm at variable load and variable speed condition while for power generation the generator runs at constant 1500 rpm under variable load condition. In the market Cummnis, Leyland CNG gas generator are available in large capacities in the range of 125 -250 kVA. Kirloskar, Prakash etc. do supply 100% Biogas generator in the range of 15-kVA-25kVA but they are costly. The aim is to provide the cheap conversion kit and to train the entrepreneur to convert the presently available (reconditioned) engine with the kit. Automotive Diesel engine runs at 3200 rpm but for power generation the engine should run at 1500 rpm. Hence, diesel engine operating at lower rpm will generate almost half the power and conversion to biogas operation will further derate to almost 50% . It was decided to develop the conversion kit for TATA 407 series automotive engine which are prevalent in the market and their spare parts are also available in the market. They can be reconditioned easily. Specifications are given in Appendix I.

In this project, New TATA-497 automotive diesel engine was converted to operate on 100% biogas. It generates 52.5 kW at 3200 rpm in diesel mode.

1.1

2.1

3.1

4.1 De-rating of the Engine

Automotive diesel engine used is TATA 497 which will produce 52.5 kW at 3200 rpm in the diesel mode. Since Generator operates at 1500 rpm, so in diesel mode the engine will produce around 26-30 kW at 1500 rpm

Whenever a diesel engine is converted for use of a gaseous fuel, particularly a dilute gaseous fuel such as biogas which contains only 55-60% combustible constituents viz. methane and the rest is CO2, there occurs necessarily reduction in the maximum power output of the engine. This is called de-rating. The main reason for this de-rating is as follows.

The engine in diesel mode takes in only air during the intake stroke while in the converted mode, it has to take in air and gaseous fuel mixture. As a result, substantial part of the cylinder is occupied by the gaseous fuel reducing the air availability per cycle which controls the maximum fuel that can be burnt per cycle, in accordance with the required air fuel ratio. Further, because of difference in calorific values of diesel (about 43 MJ/kg) and biogas (about 20 MJ/kg), the energy available in the charge per cycle is reduced. To some extent, reduction also occurs because of decrease in efficiency due to comparatively slower combustion of biogas. Even though, the air fuel ratio required for biogas is much lesser (around 6:1) as compared with diesel (around 20:1), which is an advantage for power output per cycle for biogas engine on the whole, it is usual to have the engine power de-rated to 50-55% of the original output as a result of this conversion.

5.0 Development of Governing Mechanism, Air Gas Mixture and Ignition Mechanism

5.1 Development of Governing Mechanism

The Engine speed varies with change of load i.e. as the load decreases the engine speed increases and when the load is increased the engine speed will decrease. The generator requires constant speed i.e. with any change of load the speed should remain constant.

To maintain constant speed, the Governing Mechanism consists of an Actuator, Speed Control Unit and Magnetic Speed Sensor. The Actuator lever is connected to the butter fly valve of the gas carburetor, which control the charge (air + gas mixture) going to the engine.

  • Actuator

The Electric Actuator is electric output, proportional servo. This electric magneto actuator is used as a fuel control position device, which acts on butter fly of gas carburetor with the help of linkages as shown in Plate 1

An internal spring provides fail safe operation by forcing the actuator to the charge shut of position when the actuator is de-energized. This mechanism combines fast operation multi voltage wider rotation angle. The actuator can operator directly from 12 Volt battery supply. Speed Control Unit

The speed control unit is electronic device designed to control engine speed with fast and precise response to transit load changes. This close loop control connected to a proportional electric Actuator and signal supplied by magnetic speed sensor will control the speed of engine. Magnetic speed sensor

The magnetic speed sensor detects the engine speed when ring gear teeth pass the sensor. Electrical pulses are produce by the sensor’s internal coil and sent to the speed control unit. The signal from the magnetic speed sensor, teeth per second (Hz) is directly proportional to engine speed.

The signal sent to speed control unit is further passed to Actuator.

5.2 Air Gas Mixture (Gas Carburetor)

Air gas mixture consists of diaphragm operated gas valve with gas carburetor (with butterfly) and vacuum nipple. With change of load the actuator acts on butterfly of the gas carburetor to increase or decrease of the charge to maintain constant speed. The change in vacuum is felt by the diaphragm operated gas control valve which supplies the gas in required amount.

5.3 Ignition Mechanism

Battery operated Lucas electronic ignition system has been used, as it is available in the market and suitable ignition advance has been carried out for biogas operation. It has been connected to camshaft with the help of housing.The head of the diesel engine has been modified and the spark plug (M10 x 1) has been screwed in place of injector.

6.0 Experimental Setup

6.1 Introduction

The objective of the present work was to conduct performance trials on converted diesel generator in the present work, load, speed, gas consumption was noted and thermal efficiency, specific gas consumption was calculated.

6.1 Instrumentation

The engine was fully instrumented to measure engine performance. The instruments fitted to the test rig were properly selected to minimize the possible errors during experimentation. A schematic diagram of the test rig with full instrumentation is shown in Figure-1.

6.1.1 Fuel Consumption Measurement

In order to calculate the specific fuel consumption of the engine, it was necessary to determine accurately the mass of the fuel that is consumed by the engine per unit time under the given operating conditions. Marking was done on biogas holder. Gas consumption in specific time was noted with the help of the stopwatch under various loading condition.

6.1.2 Gen-set Loading Arrangement

A resistive type loading arrangement was installed for this research work. The generator output was supplied to this loading arrangement that was designed with a combination of electric heaters. The loading system used for these experimental activities was of only resistive loads. The electric heaters were connected in a network to load the generator in various load fractions. The salient feature of the loading system was that the engine could be loaded with desired fractions of full load during experimentation. Voltage and ampere can be read from the voltmeter and ampere meter on panel box.

7.0 Results and Discussion

Introduction

All the tests and data analysis for biogas were performed on a retrofitted 100% biogas genset, the performance of a genset running on biogas with respect to power output, fuel consumption and efficiency depends very much on the composition of biogas. The composition of biogas was around 61%methane and rest carbon dioxide & others gases. The gas sample was tested in Gas Chromatograph.

The readings taken are given in the tabular form

S. No. / Load / Engine Speed / Voltage / Current / Volume Flow Rateof Biogas / Input Energy / Output Power / Brake Thermal Efficiency / Mass Flow Rate of Biogas / BSFC
kW / RPM / Volt / Ampere / m3/h / kJ/s / kW / % / kg/h / g/kWh
1 / 0 / 1540 / 450 / 0 / 6.6 / 36.8 / 0.0 / 0.0 / 7.2 / 0.0
2 / 3 / 1540 / 440 / 4 / 8.0 / 44.3 / 2.4 / 5.5 / 8.6 / 3530.9
3 / 6 / 1540 / 440 / 9 / 10.9 / 60.6 / 5.5 / 9.1 / 11.8 / 2148.0
4 / 9 / 1540 / 440 / 14 / 12.7 / 70.7 / 8.5 / 12.1 / 13.7 / 1609.1
5 / 12 / 1500 / 430 / 19 / 15.5 / 85.9 / 11.3 / 13.2 / 16.7 / 1475.22

Fig. 2 Brake Thermal Efficiency versus Load at constant 1540 RPM

The Brake thermal efficiency of a retrofitted engine for biogas depends mainly on the composition of biogas i.e. heating/calorific value and operating condition like lean/rich air-fuel mixture. The fig. 2 illustrates efficiency is increasing from 3 kW to 12 kW and is maximum around 14% at 12 kW and also the data is repetitive as many reading have been taken.

7.1 Brake Specific Fuel Consumption (BSFC)

The Brake specification consumption is around 1.5 Kg/kWh at maximum load of 12 kw.

Fig. 3 BSFC versus Load at constant 1500 RPM

Further investigations are required to reduce the BSFC. Figure - 3

8.0 Conclusions

The present study, has demonstrated that retrofitted biogas fuelled Engine Generator Set have a potential for utilization of locally available organic degradable material and significant reduction of emissions and noise. The following concluding remarks can be drawn from the present study

9.0 References

  1. Venkata, Ramana P., ”Biogas Programme in India”, a status report, Teri Information Digest on Energy 1(3): 1-12 p 196-207,1998.
  2. Mitzlaff, Klaus. Von., “Engines For Biogas”, Frieder. Vieweg & Sohn Braunschweig/Wiesbaden, 1988.
  3. Govil, G.P, Experiences of conversion of Diesel engine to 100% Biogas engine Proceedings of the National Workshop On Policy Frame Work For The Biogas Programme For The Next 10 Years’ Oct. 5-6, 2006, CRDT ,IIT Delhi
  4. Govil, G P, Gaur R R, Anand Sachin., Development of Biofuel Engines For Rural Applications, International Seminar on Downsizing Technology for Rural Development 7-9 oct. 2003, RRL Bhuwneshwar
  5. Govil, G.P., Gaur R.R., Development Of Conversion Kits To Promote the Use of Biogas in Existing Diesel Engines For Variable-Load Rural Applications, National Conference on Commercialisation Aspects of Renewable Energy Sources” Dept. of Renewable Energy Sources, College of Tec. and Agriculture Univ. Udaipur, April 28-29,2000

Appendix - I

Technical Specifications of ENGINE

Model : TATA 497

Type : Water cooled direct injection diesel engine

No. of cylinders : 4 in line

Bore / Stroke : 97 mm x 100 mm

Capacity : 2956 cc

Maximum engine output : 52.5 kW (71.3 PS) at 3200 rpm as per CMVR TAP 115/116