Dual Fuel Mode Using Producer Gas And Bio Diesel Engineering Essay

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Abstract-Partial combustion of biomass in the gasifier generates producer gas that can be used as supplementary fuel for C.I. engines. In this study, the woodchip is used as the feedstock for gasifier to generate producer gas. The gasifier-engine system is operated on diesel and Jetropha (HOME) biodiesel blends in liquid fuel mode operation and then on liquid fuel and producer gas combination in dual fuel mode operation. The performance of the CI engine is analyzed by running the engine in liquid fuel mode operation and in mixed fuel mode operation at different load conditions with respect to maximum diesel savings in the dual fuel mode operation. It was observed that specific energy consumption in the dual fuel mode of operation is found to be in the higher side at all load conditions. The brake thermal efficiency of the engine using diesel or biodiesel based on Jetropha is higher than that of dual fuel mode operation. A diesel replacement in the tune of 60% in dual fuel mode is possible with the use of woodchip producer gas. The engine performance is evaluated in dual fuel mode (Producer Gas + Diesel as a pilot fuel) and mixed fuel mode (Producer Gas + Jetropha Bio-Diesel blends and Diesel) and this performance is compared with the base line performance of the engine in terms of Brake thermal efficiency (BTE) and Brake Specific Energy consumption (BSEC) and amount of diesel replacement at different load condition.

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Keywords- C.I engine; Dual fuel mode; Producer gas; Gasifier; Bio-diesel blends.

INTRODUCTION

The energy needs of the world are increasing rapidly. The decrease in fossil fuels, emission pollution caused by them and increasing fuel prices make biomass energy sources more attractive. The world reserves of primary energy and raw materials are, obviously, limited. According to an estimate, the reserves will last for 218 years for coal, 41 years for oil, and 63 years for natural gas, under a business-as-usual scenario. The fuels of bio-origin can provide a feasible solution to this worldwide petroleum crisis. Scientists around the world have explored several alternative energy resources, which have the potential to quench the ever-increasing energy thirst of today's population. Various biofuel energy resource explored include biomass, biogas, primary alcohols, vegetable oils, etc. The increase in energy demand and decrease in oil reserves have focused attention on bio-fuels. Biodiesel is a fuel that is manufactured from vegetable oils with the help of catalysts, and may be directly used in diesel vehicles with little or no modification [1].

Compression ignition (CI) engine could be operated with fuels either alone or in the form of mixture. Use of diesel in CI engine is a well-proven technology. In India, a large variety of biomass feedstock is available in huge amounts. As these are available locally, biomass Biomass gasification is one such process where producer gas could be obtained from biomass feed stocks and in turn uses the producer gas for power generation purposes.

The utilization of producer gas in the diesel engine in dual fuel operation is an established technology for conservation of Diesel. Producer gas could be used in CI engine, without any modification in the engine. However, it cannot replace the diesel completely. Diesel replacements up to 70-90% have been achieved in the dual fuel mode. Because of its poor ignition/delay ignition characteristics some minimum amount of Diesel is required to start the ignition. On the other hand, the use of plant oil as fuel for CI engine is not new. The all properties of plant oils were close to diesel except viscosity and volatility. Various methods were adopted to overcome these problems. It included blending of oils with diesel [2].

Gasification is the process of converting solid/liquid fuel into gaseous fuel. It involves the utilization and conversion of biomass in an atmosphere of steam and/or air to produce a medium or low calorific value gas. Gasification is a form of pyrolysis, carried out at high temperatures. The ratio of oxygen to biomass is typically around 0.3. The resulting gas, known as producer gas, is a mixture of carbon monoxide, hydrogen and methane, together with carbon dioxide and nitrogen. A typical composition of producer gas generated by biomass gasification on volumetric basis is given in Table- I

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CONSTITUENTS OF PRODUCER GAS

GASIFIER-ENGINE SYSTEM

Introduction:

In the past few decades, biomass gasification has emerged as a promising route to efficient utilization of biomass, a renewable energy source which is widely available in tropical countries like India. This involves conversion of the biomass, a solid fuel, into a gaseous fuel called the producer gas. Producer gas can be used in an internal-combustion (I.C.) engine as a substitute for petroleum based fuels, to get motive power or electricity. The gasification technology enables the use of biomass for decentralized power generation, which is being increasingly looked upon as viable alternative to provide electricity and motive power to the remote rural areas of our country. Availability of electricity can, in turn, act as a catalyst for promoting rural industrialization and development. While commercial systems of this kind are already available, many organizations have put in efforts to make simple low cost gasifier, fabricated locally. In the same spirit Navreet Energy Research and Information (NERI) and SPRERI developed a gasifier-engine system (Figure-1) and tested it in the field for running a flour mill and an irrigation pump. The efficiency of conversion depends on biomass material, particle size, gas flow rate and design of chemical reactor or Gasifier [3].

Biomass gasifier:

Complete combustion of any biomass should result in formation of carbon-dioxide and water vapour, with ash as a residue. On the other hand, in a biomass gasifier, the biomass is burnt in limited supply of oxygen, not sufficient for complete combustion. This results in the formation of a combustible mixture containing carbon-monoxide, hydrogen and methane, besides the non-combustible components of carbon-dioxide and water vapour.

Wood waste Gasifier setup.

Typical composition of producer gas is: CO 15-30%, H2: 10-20%, CH4: 2-4%, CO2: 5-15%, water vapor 6-8% and the rest N2. The process involves drying of biomass followed by pyrolysis, i.e., breaking up of biomass into char and volatile matter. The reactions between the combustion products and the char at high temperature lead to the final gaseous mixture called producer gas. The final products also include some unburned volatile matter in vapor form, which can condense when the gas cools to form a sticky substance called tar. When gas is burnt in a burner for thermal application, tar does not pose much problem. [4]

However, for use in an IC engine, the gas needs to be cleaned of tar more thoroughly. The tar content must be less than 50 mg/m3, which needs an elaborate cooling and cleaning system. The tar content in the producer gas depends strongly on the design of the gasifier. Low tar content requires high temperatures, around 1200oC in the combustion zone of the gasifier. It also needs high residence time of the gas in the high temperature region [5].

Types of gasifiers:

Most of the gasifiers in the field are of two types:

Updraft type where the gas flow is upwards through the biomass and char bed, while the biomass moves down.

Downdraft type where the gas also flows downwards, in co-current with biomass.

The Downdraft type of design gives much less tar in the final gas as compared to the updraft design. However, an updraft gasifier is much simpler to build and operate but produces more tar. Hence, updraft gasifiers are more commonly used for thermal applications. The problem of tar can be overcome through another route. If charcoal is used as feedstock in the gasifier, the tar produced is much less since most of the volatile components of biomass causing tar formation have already been removed at the time of charcoal formation. Consequently a simple down draught wood waste gasifier can be used with a simple cleaning arrangement for gas to get producer gas quality suitable for use in an IC engine. This is the strategy adopted by NERI in developing their simple system for power generation [4].

Use of producer gas in dual-fuel mode engine

Producer gas can be used in I.C. engines in two ways:

In dual-fuel mode along with diesel

In dual-fuel mode along with Bio-Diesel blends and

In single fuel mode in a spark-ignition (SI) engine.

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Till recently, most systems used dual-fuel mode of operation. In this mode, a diesel engine is run on the combination of producer gas and diesel. With the use of producer gas, the diesel requirement can be reduced to about 20% of the normal requirement in the pure diesel mode. The diesel requirement is higher when the engine is run in part load. Dependence on diesel for this mode of operation can pose a problem in regions where diesel is not easily available. More importantly, with the rising cost of diesel, the economics of this mode of operation may not be very favorable.

On the other hand, operation of an engine only on producer gas requires spark-ignition. While a petrol engine

can be directly used for the purpose, it has the disadvantage of a low compression ratio of 9:1 or lower. Producer gas can be used successfully on engines with a much higher compression ratio of about 17:1. Since efficiency of operation of an engine improves with increase in compression ratio, it is more advantageous to convert a diesel engine to run on spark-ignition mode. The performance of producer gas and bio-diesel fuel blends in a diesel engine is compared with the producer gas and diesel. The blends were obtained by mixing diesel and bio-diesel in appropriate proportions [5].

Performance of a dual fuel engine fuelled with producer gas and diesel includes several parameters of interest such as thermal efficiency, power capacity, and percentage of diesel substitution at various loads and engine exhaust emission. All these performance parameters depend upon two factors, i.e., chemical properties of producer gas and basic engine design. In case of producer gas dual fuelling, it is difficult to ensure uniform gas quality as it is affected by flow conditions through the gasifier system, the pressure drop across the gasifier system and the gas temperature at the gasifier outlet, both vary with engine design and operating conditions [3].

TEST METHODOLOGY

Details of engine specification:

A single cylinder four stroke, direct injection, C.I. engine, naturally aspirated 'Field Marshal' make diesel engine is used. Detailed specification of the engine is given in Table-II

Engine specification

Details of gasifier specification:

A Downdraft wood waste gasifier, Associated Engineering Work (AEW) make having the technical collaboration with SPRERI is used for generation of producer gas Table-III.

Gasifier specification

Gasifier Unit

Type Of Gasifier

Downdraft, batch feeding

Model

GM 55

Material Of construction

M.S. except hearth and air Nozzles where S.S. is used

Rated capacity

10 to 12 m3 /hour

Air Nozzles

4 Nos.

Hopper capacity

60 kg

Fuel used

Waste woody biomass

Size of fuel

Chips of 25 mm, 10mm

Gas cooling medium

Water

Gas Clean Up Unit

Scrubber

Direct contact, co-current water jet

Filter Media

Pebble, cotton yarn waste etc.

Scrubber water flow rate

600/hour

Pressure drop

45 mm of water column

Gas Temperature

Ambient [after cooling]

Tar and Soot in gas

Negligible

Test rig and experimental procedure:

Engine Model

GF1 / GF 1B

No. of Cylinder

One

Type of Bearing

Brass / TRB

Fuel injection Timing

280 before TDC

Rated Power (as per IS:11170)

kW/Bhp

3.7 / 5.0

Rated Speed

RPM

1500

Bore x Stroke

mm

80 x 110

Cubic Capacity

CC

553

Compression Ratio

1

16.5 : 1

Sp. Fuel Cons. (at full load)

g/Kwh

236 / 240

Sp. Fuel Cons. (at full load)

g/Bhph

174 / 176

Lub. Oil Cons. (Note : 1000cc=1Lit)

cc/hr

15

Fuel Tank Capacity

Litre

9

Torque at Cam gear End

Kgm

4.8

Torque at Rated Speed on Flywheel End

Kgm

2.39 Layout of test setup: The experimental setup consists of a diesel engine, Downdraft gasifier, gas cooler, gas filter, and centrifugal pump system. The engine is modified to work in dual fuel mode by attaching a producer gas supply to the intake manifold. Under dual fuel operation part of the liquid is replaced by gaseous so as to maintain the power output of the engine the same as for normal diesel operation at specific operating point (Figure -2).

Schematic layout of the test setup

Description of the experimental procedure:

The biomass is fed to the gasifier through its bottom opening. Air enters at the combustion zone and producer gas generated leaves near the bottom of the gasifier. The hot producer gas is allowed to pass through the cooler where its temperature is reduced to atmospheric. The cooled gas with moisture is then passed through the filter to remove tar and other particles. Gas passes through pebble bed and then through bubble cap filter column. Later it allowed passing through cotton yarn column for absorbing the moisture and security filter for fine filtering. At the outlet of filter pipe a valve is provided to control the gas flow. A gas flow meter connected to the out let pipe to measure the producer gas flow rate. The producer gas and air are mixed in the intake pipe and the mixture enters into the engine (Figure -3).

Schematic of experimental set up

The increase in air flow rate decreases the gas flow rate to the intake, as the sum of air and gas flow rate is almost remains constant. For different ratio of producer gas + diesel and producer gas + bio-diesel the performances is carry out for the different loads. Then supply of producer gas closed and run the engine only on diesel for some period, then starts the supply of Bio-Diesel blend in dual fuel mode with the diesel and the performance is carry out for the different load conditions.

The diesel and jatropha oil fuel blends were tested successfully in the unmodified diesel engine. Test runs were also carried on straight (pure) jatropha oil and diesel oil fuel in order to make comparative assessments. The engine ran well on all the fuels except that in each case there was a need to warm up the engine slightly. The effects the straight jatropha oil and a blend of equal volumes of the jatropha oil and the diesel fuel on engine performance was also investigated.

Physical and chemical properties

Standard methods (i.e. ASTM and I.P. methods) were used to determine the properties of the jatropha oil and its blends at the Tema Oil Refinery (TOR), Tema, Ghana with the exception of the calorific values, which were determined at the Mechanical Engineering Combustion Laboratory of the KNUST, Kumasi. The chemical and physical properties of the jetropha oil and its blends relative to the diesel fuel are provided alongside the TOR limit for their product specification of diesel in Table-IV [5].

Chemical and physical properties of jatropha oil and its blends relative to diesel fuel

Results and discussion

Characterization of Liquid fuels:

The important properties of HOME and B20 are quiet comparable with diesel as given in Table V [5].

PHYSICO-CHEMICAL PROPERTIES OF LIQUID FUELS

Composition and Calorific Value of Producer Gas:

Based upon the producer gas composition, the calorific values are calculated and it is tabulated in Table - VI. Average calorific value of 4.3844 MJ/m3 observed for the producer gas is taken for further calculation. The calorific value of producer gas derived from wood chip and coir-pitch are 4.8MJ/kg and 3.5 MJ/kg respectively [6].

Composition and Calorific Value of Producer Gas

Performance of CI Engine in Dual Fuels Mode (Liquid fuel and Producer Gas):

While operating the gasifier CI engine system, liquid fuel economy is one of the major factors. The engine performance with diesel, Jetropha blends, Diesel + PG, Diesel + PG + jetropha blends is evaluated in terms of BTE, BSEC, along with emission characteristics at 0, 25,50,75 and 98% loading conditions of the engine is discussed below.

Brake thermal efficiency:

The use of producer gas in dual fuel mode operation reduces the consumption of pilot fuels, like diesel or jetropha blends. The percentage savings of diesel is higher than that of jetropha blends in dual fuel mode operation because of its better fuel burning qualities. The pilot fuel savings decreases at higher loads in both cases either oil or diesel. At higher loads, the lower calorific value of producer gas and the incomplete combustion reduces the pilot fuel replacement remarkably fig-4.

Comparison of brake thermal efficiency of engine with various fuels

Liquid Fuel Replacement(LFR) and Liquid Fuel

Consumption Rate (LFCR):

Both the term LFR and LFCR are interrelated terms. The LFR in dual fuel mode operation is calculated as,

Liquid: (Diesel, jetropha and B20) and dual: (Diesel + PG, jetropha + PG and B20 + PG). Fig. 5, explain the LFCR with liquid fuel and dual fuel mode. The liquid fuel consumption is more with HOME in comparison with diesel and B20. The considerable drop of LFCR is observed when the engine is operated in dual fuel mode. From figure-5, it can be easily seen that mean liquid fuel replacement of 46%, 50%, 55.5%, 60.36% and 26.24% is observed for 0, 25, 50, 75 and 98% loading respectively. Maximum LFR of in the tune of 59-61% is observed for all the dual fuel mode combinations. With the increase in producer gas flow rates, the LFR increases. It can be seen that the maximum LFR has gone up to 60.91% in diesel + PG mode. The decrease in LFR is observed high load conditions. At high load operations, insufficient gas flow decreases the LFR. In order to reduce detonation, the intake of producer gas is reduced resulting in a low liquid fuel replacement at high load fig-5.

Variation of LFCR with applied load in liquid fuel and dual fuel mode

Specific energy consumption:

Specific energy consumption in dual fuel mode operation is higher than that of diesel mode at all operating conditions. From Fig, the specific energy consumption of rubber seed oil-producer gas engine is much higher than that of diesel engine fig-6.

Comparison of specific energy consumption of engine with various fuels

Also, at higher percentage of producer gas flow, specific energy consumption was found to be higher. In dual fuel mode operation with vegetable oil-producer gas, the specific energy consumption was found to be higher than that of neat diesel or neat vegetable oil. The poor fuel atomization and reduction in air flow leads to incomplete combustion and increase the specific energy consumption.

Emission:

The performance and emission characteristics of the dual fuel engine are compared with that of diesel engine at different load conditions. Specific energy consumption in the dual-fuel mode of operation with oil-coir-pith operation is found to be in the higher side at all load conditions. Exhaust emission was found to be higher in the case of dual fuel mode of operation as compared to neat diesel operation fig-7.

Emission characteristics of the dual fuel engine with various fuels

Engine performance characteristics are inferior in fully renewable fueled engine operation but it suitable for stationary engine application, particularly power generation.

Acknowledgment

This work is supported by Government College of engineering, Amravati (Autonomous) Masters Degree program. Author is sincerely thankful to Dr. P. M. Khodke, Dr. R. S. Dalu and Dr. R. B. Yarasu for their kind support. The contents of this paper are solely the responsibility of the author.

CONCLUSIONS

Growing demand of petroleum fuels and their limited availability in the country have necessitated the search for the replacement of these fuels. In the present work the effect of dual fuel combustion on performance of an existing direct injection diesel is studied.

The engine has been properly modified to operate under dual fuel operation and its basic configuration has been maintained. From the literature study it is revealed that dual fuel operation results to higher ignition delays compared to normal diesel operation. Thus it seen that the dual fuel mode of combustion using Producer gas and bio-diesel as a supplement for liquid fuel is a promising technique for reducing the quantity of fuel required on existing C.I diesel engines requiring minimum modifications having no danger for the engine structure .

The most promising results can be obtained with Producer gas and diesel in dual fuel mode and high engine loads. The specific diesel fuel consumption reduced significantly when operated on the Dual fuel Mode as compared to producer gas operation, because of supply of Bio-diesel blends which reduced the diesel need. The important findings are listed below.

The existing diesel engine is capable of successful running in dual-fuel mode of operation with biomass.

The woodchip biomass having good calorific value and low ash content that makes it suitable feedstock for biomass gasification with no modification in the gasifier.

Maximum liquid fuel replacement in the tune of 60% is achieved in all duel fuel mode operations, with no engine modification.

In dual fuel mode operation the engine performance decreases, with increased emissions at all load conditions.

This study proved that the diesel engine is capable of successful running in dual fuel mode of operation with the woodchip as biomass in the gasifier.

Carbon monoxide emission in dual fuel mode of operation is higher than that of liquid fuel operation.