| 
  • If you are citizen of an European Union member nation, you may not use this service unless you are at least 16 years old.

  • Work with all your cloud files (Drive, Dropbox, and Slack and Gmail attachments) and documents (Google Docs, Sheets, and Notion) in one place. Try Dokkio (from the makers of PBworks) for free. Now available on the web, Mac, Windows, and as a Chrome extension!

View
 

Gasifier Go-Kart

Page history last edited by David A. Gagnon 11 years, 2 months ago

Brown University Engineering 1000: Fall 2009 Projects


 

 

 

 

Gasifier Powered Go-Kart

 

 

Brian Fisher, David Gagnon, and Devin Sutcliffe

 

 

 


 

 Abstract

 

 

We are building a small one person vehicle that will run on wood gas.  This project will serve as an example of the alternative fuels that can be used to run internal combustion engines.  Our goal is to make a gasifier that is small, safe, and convenient at low cost.   This gasifier will be mated with a standard go-kart engine and mounted on a go-kart frame.  The output gases from the gasifier will serve as the engine's only fuel input.

 


 

 Introduction to Gasification 

 

Fossil fuels are not a renewable source of energy.  They are also not readily available in unpopulated areas and can be very costly.  We want to build a go-kart with an internal combustion engine that can function solely using wood as fuel.  This would allow people who live far from available fuels or wish to save money by running their vehicles without gasoline an alternative means of transportation.  This may also help to address a potential disaster that could occur if the price of fossil fuels was to skyrocket or the supply was to decline substantially.  In addition, gasification is an environmentally friendly carbon-closed process, meaning that the only greenhouse gases generated are those absorbed by the tree that produced the wood chips.

 

Gasification of carbon based fuels has been explored since the 19th century.  Coal was initially gasified to provide light, heat, and cooking fuel.  Once the internal combustion engine became widespread, gasified coal was the standard industrial fuel.  The proliferation of petrol-based fuels in the early 20th century caused gasification use to widely decrease.  However, the sacrifices of World War II pressured the United States and Great Britain to impose restrictions on civilian petroleum usage.  As a result, gasifier use skyrocketed, and some historians estimate gasifier usage was in the millions of units.  Gasification is still used today to produce power, most notably in Gussing, Austria, where the European Union has constructed a two megawatt power plant run entirely on wood gas.  In addition, gasification has been discussed by major national and internation organizations as a clean burning fuel and a source of power in a crisis.  Documentation includes Construction of a Simplified Wood Gas Generator for Fueling Internal Combustion Engines in a Petroleum Emergency by the United States Federal Emergency Management Agency (FEMA), FAO Forestry Paper 72 by the United Nations, and Technical Paper 296 by the World Bank.

  


 

Theory

 

The process of creating wood gas, also known as synthesis gas, at its most basic, is merely incomplete or choked combustion.  However, gasification is truly made up of four distinct processes within the unit.  These four processes are drying, pyrolysis, combustion, and reduction.  A summary of the gasification processes is shown below in Figure 1. 

 

 

Drying

All moisture must be removed from the wood chips in order to successfully produce wood gas.  While all water in the wood will be vaporized eventually by heat of pyrolysis, combustion, and reduction, failure to remove moisture from the wood beforehand results in the inability to produce clean fuel.  Therefore, in an ideal gasifier, some of the heat produced during combustion is used to completely dry the wood.  Since the lack of clean gas could be catastrophic to our project, we have chosen to either pre-bake or purchase pre-dried wood chips (www.gekgasifier.com).

 

 

Pyrolysis

Pyrolysis occurs when the wood chips are heated without enough oxygen to burn.   Fast pyrolysis does not begin until the wood has reached a minimum temperature of about 550 K (Engineering Toolbox).   This causes the wood chips to decompose into tars (gasses and liquids) and charcoal.  The tars are burned off, leaving charcoal with a high carbon content.  This charcoal is integral for the reduction process (www.gekgasifer.com).

 

 

Combustion

Combustion is the exothermic combination of hydrocarbons with oxygen.  The heat for all processes is generated from combustion of the tars produced during pyrolysis.  In addition, combustion produces carbon dioxide and hydrogen gas, which will become reactants in the reduction step.  Adequate mixing and high temperature flame is key, since the lack of either could permit the tars to still be present in the wood gas, which in turn could lead to engine failure.  Therefore, producing clean fuel is largely dependent on the combustion dynamics in the gasifier (www.gekgasifier.com)  The United Nations Forestry and Agriculture Organization suggests that the combustion zone should reach a minimum of 1473 K to ensure a clean burning fuel (FAO 72, 34).

 

 

Reduction 

Reduction reverts completely combusted hydrocarbons into a form that can be used as fuel.  Note that reduction is the opposite of combustion - it is the endothermic removal of oxygen from hydrocarbons.  Typically combustion and reduction exist in equilibrium in any burning process.  Reduction in a gasifier occurs when carbon dioxide and water vapor flows through heated charcoal (primarily carbon).  The heated carbon removes the oxygen from both the carbon dioxide and the water vapor.  The oxygen is spread to the carbon atoms, forming covalent bonds in the form of carbon monoxide.  Oxygen has a higher affinity for carbon than either hydrogen or itself.  This leaves the remaining hydrogen atoms to form their natural diatomic.  Therefore, two reactions occur from the addition of carbon and heat:  carbon dioxide is reduced to carbon monoxide and water vapor is reduced to diatomic hydrogen and carbon monoxide (www.gekgasifier.com).  The FAO study found that the rate of reduction is only high enough to run a gasifier at temperatures above about 973 K (17).  A summary of the reduction reaction is shown below in Figure 2.

 

Figure 1: Summary of Gasification Processes (www.gekgasifier.com) 

 

 

 Figure 2: Reduction Process (www.gekgasifier.com)

 

Post-Reduction

After the reduction process, the products are ready for combustion once again.  These gases will be drawn into the cylinders of an internal combustion engine.  There, they will be mixed with air, compressed, and then ignited to produce power for the go-kart.  The additional oxygen present in the air will react with carbon monoxide to form carbon dioxide and with hydrogen to form water vapor as products, which will be our primary exhaust components.

 


 

Types of Gasifier Units

 

                                                             Figure 3:  Updraft Gasifier (www.gekgasifier.com)

    

 

                                                               Figure 4:  Downdraft Gasifier (www.gekgasifier.com)

 

                                                               Figure 5:  Crossdraft Gasifier (www.gekgasifier.com)


 

 Existing and Potential Solutions

 

There are a variety of commercially available gasifiers that can be purchased to run most internal combustion engines.  There is also a variety of information available on the Internet that describes how to build your own gasifier.  The solutions we have found are shown below with web links:

 

Construction of a Simplified Wood Gas Generator for Fueling Internal Combustion Engines in a Petroleum Emergency, United States Federal Emergency Management Agency (FEMA)

 

Small-Scale Biomass Gasifiers for Heat and Power, World Bank (World Bank Technical Paper 296)

 

Wood Gas as Engine Fuel, Food and Agriculture Organization of the United Nations (FAO 72)

 

Gasifier “Tars”:  Their Nature, Formation, and Conversions, National Renewable Energy Laboratory (United States Department of Energy)

 

Handbook of Biomass Downdraft Gasifier Engine Systems, Solar Energy Research Institute (United States Deparment of Energy)

 

ALL Power Labs

 

Gasifier Experimenters Kit

 

 

 

Good

Bad

FEMA

Simple, emergency fuel production can function effectively if built correctly.  Inexpensive and can be built with readily available parts and equipment.

Downdraft design can cause the oxidation zone to increase, decreasing the burning temperature, and increasing tar production.  This tar causes a dirty fuel stream, and can destroy the engine quite quickly.

GEK Gasifier

Robust and efficient.

Very expensive and requires more advanced parts and equipment, including a CNC mill.

 


 

Challenges

 

Initially, gasification seems like a fairly simple solution.  However, as the saying goes, the devil is in the details.  First, when the gasifier is initially lit, an inline blower must be used to pull air through the system to maintain oxygen flow to the growing fire and increase the flow rate of wood gas.  After the wood is lit and the gasifier is producing wood gas, the engine's carburetor must have sufficient suction to keep the gas flowing into the engine.  The wood gas that is produced by the gasifier must be sufficiently filtered to remove particulates and condensation and cooled before it enters the carburetor of the engine to prevent power loss and protect the engine.  A filter that can remove particles as small at 40 microns is ideal (FAO 72, 15).  Lastly, because of the lower heating value of woodgas versus gasoline, we can expect a minimum power loss of 35% (FAO 72, 10).

 


 

 Intellectual Property

 

A few patents pertaining to gasification are listed below:

1)  Rundstrom

Inventors: Rundstrom; David A. (Huntington Beach, CA)
Assignee: Southern California Edison (Rosemead, CA)
Appl. No.: 07/655,764
Filed: February 13, 1991

 

An industrial scale updraft gasifier capable of turning wood waste meant for landfills into wood gas for energy generation. This would be a stationary system capable of turning about 1225 lb/hour of wood products into 2840 lb/hour of producer gas with a total of 7.4E6 BTU/hour.

 

 

2) Sunter, Neufeld, and Wiles

  Inventors:     Sunter; Richard (Malahat, CA), Neufeld; Jake (Victoria, CA), Wiles; David (Victoria, CA)

  Assignee:     Malahat Systems Corporation (Victoria, CA)

  Appl. No.:     09/978,692

  Filed:           October 18, 2001

  

A portable gasifier that uses a reservoir of water as part of the wood gas filtration system. This system would run a stationary internal combustion engine.

 

 

3) Milner, Butler, and Ashworth 

  Inventors:     Milner; Geoffrey (Stockton-on-Tees, GB2), Butler; Michael F. (Lakeland, FL), Ashworth; Robert A. (St. Petersburg, FL)

  Assignee:     DM International, Inc. (Houston, TX)

  Appl. No.:     06/438,652

  Filed:           November 2, 1982

Commercial scale gasifier for the production of Methanol. The gasifier uses wood chunks and produces about 11000m^3/hour of wood gas.

 

 

The majority of US patents that pertain to gasification are large scale industrial applications, not small scale gasifiers for propulsion of vehicles. In addition, we have not found any gasifiers that are meant to be mobile and run an engine as small as ours.

 


 

Design Criteria

 

 

Requirements and Evaluation Criteria

-  The gasifier must be able to keep the engine running for at least one hour.

-  The go kart must be able to reach 15 miles per hour while operating on wood gas.

-  The go kart should be able to carry one passenger (200 pounds).

-  The gasifier must not burn, or be otherwise hazardous, to the driver of the vehicle.

 

 

Constraints

- The gasifier must be the only source of fuel for the go kart and fit securely on the go kart frame

- The total cost for the project must be under $1000

 


  

First Prototype (Design 1)

 

 

DATE:  September 17th through October 1st

  

In order to create the first prototype, we had to determine the dimensions necessary for the gasifier to work effectively and power a 5.5 hp engine. The three main reasons for the dimensions of the gasifier that we are proposing are that the fire tube must be wide enough that the fuel does not get stuck in it, the fire tube must be long enough to complete pyrolysis, combustion and reduction, and the hopper must hold enough fuel to run the gasifier for at least one hour without refilling.

 

The GEK design has a 3” diameter opening as their smallest fuel feedthrough, so we decided that this should be the smallest fuel feedthrough diameter that we use as well. We want the firetube to be as thin as possible so the flow rate for combustion is as large as possible and the temperatures in the fire tube stay hot enough to produce low tar wood gas even with a small engine. The reason that the fire tube is not smaller than 3” is that the smaller the fire tube, the more likely it is that the fuel will clump and not fall into the fire tube.

 

The length of the fire tube was chosen because the schematic for the FEMA gasifier has the fire tube length about 2.5 times its diameter, so that is what we chose to do as well.

 

The average density for wood is around 575kg/m^3. On average, one kg of wood produces about 2m^3 of woodgas. An engine uses about 2m^3/hour of woodgas per hp to run. We are planning on using a 5.5hp engine, so we rounded up to 6kg/hour of wood to run our engine. Since we want to be able to run our gasifier for 1 hour without refilling the hopper and the packing of woodchips is about 40% efficient, our hopper needs to be a minimum of 26L. Because we believe that our gasifier will have unforeseen losses and all of the fuel may not make it from the hopper into the fire tube, we have a margin of error of about 2. Therefore we decided on a hopper volume of 50L in addition to the volume of the fire tube (4L).

 

The air intake is on the side of the gasifier so that the air is heated before it enters the hopper, facilitating pyrolysis ,keeping the outside of the gasifier cooler, and making the gasifier more efficient.

  

Sources

 

Density of wood:

http://www.simetric.co.uk/si_wood.htm

 

Density of woodchips: 

http://www.bioheat.info/pdf/kpn_wood_fuels_at.pdf

 

How much wood needed: 

http://www.gekgasifier.com/about/resources-for-gasification/

 

Dimensions of fire tube: 

http://www.gekgasifier.com/forums/showthread.php?p=740#post740

 

Creating a basic woodgas carburetor:

http://gekgasifier.pbworks.com/How-to-Make-a-Woodgas-Carburetor

 

Figure 6:  Gasifier Schematic #1

 

This initial prototype was determined to be too complicated for the first build.  We decided to go for a design that was a bit simpler and used less materials to start.

 


 

First Prototype (Design 2):

 

 

DATE:  October 1st through Oct 22

 

For the first prototype (round 2), we tried to simplify the design in order to use less steel and be easier to fabricate.  The go kart was also worked on in order to get it functioning so that it ran on regular gasoline.  After this is complete, we can convert it to run on wood gas produced by our gasifier.

 

 

Figure 7:  Gasifier Schematic #2

 

 

 

The frame for the go-kart was obtained free of charge and a picture is shown below.

 

Figure 8: Go-Kart Frame

 

 

The engine was ordered from eBay and is shown in Figure 9.  It is a 5.5 hp Tecumseh engine with a 3 amp alternator.

 

Figure 9:  Tecumseh 5.5 hp Engine

 

 

The filter is in progress and the design is based on an empty paint can filled with wood chips as the filter material.  In order to absorb water, the wood chips will be placed on a mesh screen above rice, which will be used as a desiccant.  As the air flows through the system, water will drip through the screen and be absorbed by the rice.  The filter (in progress) is shown below.  Flanges at the top and the side will be added in order to allow pipe to be attached that will carry the wood gas. 

 

Figure 10: Filter with Installed Mesh

 

 

The gasifier itself will be made from 1/16" steel rolled into a cylinder.  The fire tube, or the portion of the gasifier containing the burning wood chips, will consist of a tube scavenged from a scrap metal yard.  The tube was sand blasted in order to allow it to be welded to sheet metal.  The fire tube is shown below.  It will be cut to 12" and is made of 1/4" steel.  

 

Figure 11:  First Fire Tube (Cast Iron)

 

 

The go kart frame is not entirely complete and needs some additional parts in order to function.  A brake line was installed and a makeshift steering wheel in the form of an aluminum bar was also added.  The clutch and the tires are being ordered and should be attached with the engine once they arrive.  A seat also needs to be added, and the alignment of the front wheels needs to be adjusted.  After these additions are made, the go kart should function correctly on standard gasoline.

 

A battery has been purchased in order to supply power to the blower (which is still to be ordered).  The engine has a 3 amp 12 volt alternator which will charge the battery and provide sufficient power to the blower as well as lights that may be installed.

 

In order to complete the first prototype, the following steps are underway:

 

-  The fire tube must be cut to 12"

-  The sheet metal must be rolled in welded into the correct shape as prescribed by the schematic at the beginning of this section

-  The filter must be finalized with pipe fitting for the gas to travel through and filled with wood chips and rice to absorb the water

-  The blower must be purchased and attached to the gasifier

-  Additional steel has to be purchased to provide a mount for the gasifier unit

-  A seat must be installed

-  Pipes for the gas to travel through from the gasifier to the filter and from the filter to the engine must be installed

-  The grate for the end of the fire tube must be fabricated

-  The wheels for the go kart must be attached

 

After these steps are taken, the first protype of the gasifier will be complete.

 


  

 

First Prototype (Design 3)

 

  

 DATE:  October 22nd through October 29th

 

The engine was mounted on the go kart along with the friction clutch and the gear for the chain drive.  A seat was added to the go kart as well and a brake line was installed.  The filter was completed and the fire tube was cut to the correct length.  The grate for the end of the fire tube was also fabricated. 

 

The technical aspects of fabrication were discussed with a professional who advised us to change the design slightly in order to make fabrication easier.  After talking to the person who will be welding our project together, we learned that there is a significant difference between a design and what can actually be fabricated.   Our initial designs were not plausible to weld and fabricate due to their complexity.  Some pieces needed to be welded into a very small area which the welder could not reach.  Below you will find pictures of the new design, (drawn in CAD), as well as the go kart frame with the engine installed, the finished filter, the blower, and the grate.

 

Figures 12-13:  Gasifier Schematic #3

 

 

 

Figure 14: Frame with Clutch, Engine, and Seat

 

 

Figure 15: The Finished Filter with Pipe Fittings

 

 

Figure 16: The Blower to Start the Gasifier

 

 

Figure 17: Grate for the Fire Tube

 

 

 

In order to complete the first prototype, the following steps are underway: 

-  The sheet metal must be rolled in welded into the correct shape as prescribed by the schematic at the beginning of this section

-  The blower must be attached to the gasifier

-  Additional steel has to be obtained and welded to provide a mount for the gasifier unit

-  Pipes for the gas to travel through from the gasifier to the filter and from the filter to the engine must be installed

-  Woodchips to run the gasifier must be purchased and dried

-  The wheels for the go kart must be attached

 

  

DATE:  October 29th through November 5th

 

The CAD diagram was changed to be two pieces rather than three in order to save on fabrication time.  The components were given to a professional welder to begin the fabrication process.  During the welding process, we were informed of some issues with the fire tube.  The first fire tube we obtained was from a metal scrap yard.  It was long enough for our design, with ¼” walls and a diameter very similar to what we were looking for.  We were able to get the piece from the scrap yard at no cost, and had it sandblasted to remove the rust so that it would be welded.  When the gasifier was being welded, however, there were problems with the fire tube because it was cast iron and not steel.  Unfortunately, the welds were cracking and the fire tube had to be swapped out for a steel one.

 

Figures 18-19:  Gasifier Schematic #4

 

 

 

DATE:  November 5th through November 12th 

 

We got all of the components of the go-kart functioning including the mounting of the wheels.  Unfortunately, the wheels came with the wrong screw holes drilled and had to be re-drilled in order to fit on the go kart.  The first test run on gasoline was successful and the go-kart ran adequately.  The throttle line and idle were adjusted to work properly and everything ran fairly smoothly.  However, after a few minutes of testing the chain broke.  We also realized the steering handle was very weak and needed to be replaced.  A new chain was ordered and a new handle was fabricated.  Lastly, minor design changes were made to the grate, lighting port, exhaust port, and cleaning port.  A final schematic is shown in Figures 20-21.

 

Figures 20-21:  Final Gasifier Schematic with Part Drawings (#5)

 

Below, you will find pictures of the gasifier (in progress) as well as the new chain and the final filter with a flexible duct hose attached.

 

Figures 22-26:  Completion as of November 12th

 

 

 

In order for the gasifier go kart to be completed, the following steps must be taken:

-  The fabrication of the gasifier unit must be completed

-  The blower must be attached to the gasifier

-  Additional steel has to be obtained and attached to the frame to provide a mount for the gasifier unit

-  Woodchips to run the gasifier must be purchased

 

 

DATE:  November 12th through November 19th 

 

This week we were still waiting for the gasifier to be completed.  In preparation, an aluminum frame was added to the rear of the go kart frame in order to provide a surface for the gasifier to attach to.  A back support that doubles as a wall to provide insulation from the heat of the gasifier was attached to the seat with gusset plates and rear wooden supports.  We also bought woodchips for the gasifier and dried them out by cooking them at 250 degrees for about three hours. 

   

Figure 27:  Vehicle Completion through Thanksgiving

 

 

 

 

DATE:  November 19th through December 3rd 

 

The welding of all the parts of the gasifier was finally completed.  We filled the gasifier with dried woodchips and took it outside to give it its first test.  Getting the firetube to stay lit was difficult because of the lack of oxygen in the bottom portion of the gasifier.  After the blower was attached to the top it was much easier and by creating positive pressure in the top portion of the gasifier, hot, clear gases were expelled from the gas out port.  We soon realized that these gases were way too hot to pipe directly into the filter and more cooling was necessary.  In order to cool the gas, piping was purchased that the gas would travel through in order to allow it to cool.  The pipe lengths were 3 feet and 3.5 ft and would one would span up out of the gasifier, connected to the other with a 180 degree pipe which would allow the filter to be placed on the end of the second pipe near the frame of the go kart. 

 

The positive pressure created by the blower forced too much oxygen into the gasifier and made the wood burn too quickly and at too high a temperature.  In order for incomplete combustion to occur, there must be limited oxygen in the gasifier unit.  We decided it was necessary to make the blower pull gas through the system rather than pushing air into the system.  Additionally, we added a piece of sheet aluminum that could control the opening in the top of the gasifier.  This would allow us to adjust the air intake of the system.

  

Figure 28:  Initial Test of the Gasifier:

  

 

The engine we purchased was a Tecumseh 5.5 hp engine with a 3 amp alternator.  This alternator would allow us to charge the battery for the blower off of the energy created by the wood chips, and thus provide a sustainable power solution.  After the wiring was run from the alternator to the battery, the go-kart did not have sufficient power to drive because it was using most of its power to charge the battery.  This led us to install a switch onto the alternator wiring so that we could choose whether to turn the alternator on and charge the battery or turn it off and drive the go kart.  We also added a switch in the wiring for the blower so it was not constantly running.  A 5 amp fuse was added to the wiring to ensure that if there was a short in the wires, the wires would not melt. 

 

A valve network for an air intake valve, wood gas intake valve, and a valve for the blower to pull wood gas through the system was designed and built.  A valve was added to the gas line to allow the gas flow to be shut off so that the engine could start on normal gasoline and switch over to wood gas.  Putting all the pieces together required extensive extra support systems and a bit of creative workmanship to make it all fit.  Below are pictures of the final product:

 

Figure 29:  Gas Cut-Off Valve

 

 

 

Figure 30-31: Completed First Prototype

 

 

 Figure 32:  Close-Up of Valve System

 

 

 

 

Choosing a Fuel

Initially, we had difficulty getting wood chips to run the gasifier on.  There were no suppliers that we could find in the Providence area.  However, we did get some wet wood chips from a landscaper near Boston.  Unfortunately, these wood chips were smaller than the recommended size of ¼” by ¼” by ¾”.  We used a plastic grate to filter out the smaller chips and retain only the larger one.  These chips were very damp and were then cooked in an oven on 230 degrees for three to four hours.

 

Initial testing revealed substantial amounts of tar produced by these wood chips.  We concluded that these wood chips were likely pine, and the tar was created from pine resin.  These wood chips would not be a viable solution for running the engine long term because they would clog the filter and eventually destroy the engine.  We decided to buy some wood pellets commonly used for wood stoves.  These pellets were made of hardwood and burned much cleaner than the pine wood chips.  Although smaller than the recommended dimensions, the wood pellets were found to produce sufficient wood gas. 

 

Redesigning the Grate (Grate Prototype 2)

One major design flaw was the gap between the fire tube and the grate.  This was originally included so that the fire tube would be easy to clean.  When we first started the engine on gasoline, the vibration in the frame was causing the wood chips to exit the fire tube.  This prevented any chips from fully combusting into charcoal, which is necessary to produce wood gas.  This solution was to weld a mesh around the gap between the grate and the fire tube, thereby trapping the wood chips in the combustion zone and the charcoal in the reduction zone.

 

Initial Start-up Procedure  

The initial start-up procedure for the gasifier involves first ensuring that there is enough charcoal on the grate for reduction to occur.  If there is no charcoal on the grate it can be created.  First, soak a rag in alcohol.  Then fill the fire tube with woodchips and light the rag.  Let the gasifier act as a chimney until the wood is converted to charcoal.   After charcoal is successfully created, fill the gasifier at least two-thirds full of wood chips.  This allows the wood chips above the fire tube to dry and also restricts the airflow so that wood gas is created rather than combusted.  Before lighting the gasifier, allow the blower to run for at least 30 seconds to ensure there are no flammable gases in the gasifier that could potentially explode upon ignition. Then, open the ignition port and light the charcoal with a torch and turn the blower on.  Once the exhaust from the blower will hold a sustained flame, the gas is rich enough to be used to run the engine.

  

First Test

The first time we attempted to start the engine on wood gas, we had the engine running on gasoline and simply opened the valve to allow the wood gas to enter the carburetor of the engine.  This led to the engine cutting out almost immediately.  After the engine stopped, it would not start for five to ten minutes.  We realized that the engine was likely being flooded by too much fuel, since the wood gas and the gasoline were both being added to the engine.

 

Installing a New Filter (Filter Prototype 2)

We found that the first filter we built was leaking tar-enriched liquid.  Due to the wood gas being too wet, smoky, full of tar, and leaking, we concluded that we should create a new filter.  We used an industrial size paint bucket with bulkhead fittings as our base filter.  Then we added a partition in the bucket with sheet aluminum and rubber insulation strips.  This would force the exhaust gases to travel down one chamber, under the partition, and then up the second chamber.  This effectively forced the condensation in the fuel stream to remain at the bottom of the bucket.  Lastly, we filled both partitions with wood pellets.  An image of the second filter prototype can be seen below in Figures 33 and 34.

 

 Figure 33:  Second Filter Prototype Attached to Gasifier

 

Figure 34:  Second Filter Prototype After Test Run

 

Second Test

In order to run the engine on wood gas successfully, we warmed the engine up for about 10 minutes by running it on gasoline.  Then we turned the valve on the gas line of the engine to cut the gasoline.  The engine ran for another minute on the remaining gas in the line and then quit.  At this point, no more gasoline would be added to the engine.  Then, when the wood gas coming out of the blower was rich enough to sustain a flame, we opened the valve to the engine, cut the valve to the blower, and left the air valve fully open.  After attempting to start the engine with no success, we closed the air valve three quarters of the way and tried to start the engine again.  When the engine started to turn over, the air valve was opened to almost all the way open.  This allowed the wood gas to be pulled into the engine and then allowed enough air to be added to the wood gas in about a 1:1 ratio.  Once the engine started, the air valve could be adjusted to the optimal position, which was about three quarters of the way open.  This seemed to give the engine the most power.

 

Video 1: Gasifier Walk-through

 

YouTube plugin error  

 

 

 

 

Video 2:  Demonstration of Vehicle Running Solely on Wood Gas

 

YouTube plugin error

 

 

 

 

 

 

Measurements

 

A thermocouple was used to acquire temperature measurements at various points on the skin of the gasifier system while the gasifier was producing wood gas. The engine was not running during these measurements, the wood gas was exhausting through the blower. The ambient temperature was 271K at the time of the temperature measurements. The picture below shows the positions where the thermocouple was placed and the temperature that it read. For clarity, the thermocouple read the temperature of the exhaust gas at the blower, not the temperature of the blower itself.  The temperatures seem lower than expected and may be due to poor contact between the thermocouple and the surface being measured. 

 

Figure 35:  Temperature Measurements During Normal Operation

 

 

 

Figure 36:  ABAQUS/CAE Thermal Model

 

 

A model of the heat flow in the gasifier was done in ABAQUS, a finite element analysis program. As the temperature of the fire tube is not known, it was assumed to be the temperature of the wood combustion, 1473K.

 

Modeling the heat flow through the gasifier was done using a simplified model and only included conduction and radiation.  Since gas is flowing through the gasifier during operation, forced convection should be part of the analysis as well, but forced convection is not supported in ABAQUS/CAE, so it was omitted from the analysis.  All parts of the model conduct heat, but not all surfaces radiate.  The insides of the fire tube and hopper are filled with wood pellets, so these areas are modeled as not radiating.  The outside of the fire tube is concentric with the inside of the gas tube.  All of the surfaces within the gas tube were modeled with a cavity radiation.  ABAQUS executes a cavity radiation by having all of the surfaces surrounding the cavity radiate at the average temperature of those surfaces.  This is a representative approximation because the gas tube will be filled with gas during the gasifier operation and that gas should all be about the same temperature while in this region.  All external surfaces of the gasifier were modeled as radiating to ambient at 290K.

 

The difference in ambient temperatures between the model and where the temperature measurements were taken is less than 20K, so this temperature difference does not account for the large difference between the model and measured temperatures.  Clearly, the forced convection within the gasifier and convection on the skin of the gasifier has a large effect on the temperature of the gasifier.

 

It is possible that the thermocouples were not reading an accurate temperature, but the majority of the difference is due to the model. Even if the fire tube temperature is chosen to be only 1000K, the minimum temperature for wood gas production, the temperature of the outer skin of the gasifier near the gas ports is still about 550K in the model. This temperature is over 100K hotter than what the thermocouple read for that same area.

 


 

Evaluation of Design Criteria

 

Requirements and Evaluation Criteria Completion
Comments

The gasifier must be able to keep the engine running for at least one hour.

Yes 

On one hopper of wood chips, we were able to run the engine on wood gas for well over one hour.

The go-kart must be able to reach 15 miles per hour while operating on wood gas.

 

Yes

Though wood gas only runs the engine at 50-60% of peak power, the go-kart definitely runs at least 15 mph once the air-fuel ratio is properly set.

The go-kart should be able to carry one passenger (200 pounds).

Yes

We have successfully driven the go-kart despite the added weight of the gasifier and all its components (150-200 pounds).
The gasifier must not burn, or be otherwise hazardous, to the driver of the vehicle.

 

 Yes

A concrete firewall was installed behind the seat to ensure safety.  In addition, any hazardous exhaust gases are vented away from the driver
Constraints    

 

The gasifier must be the only source of fuel for the go kart and fit securely on the go kart frame

 

 

Yes

The go-kart retains the ability to run on gasoline.  However, it can be started and run purely on wood gas.  In addition, the gasifier is securely bolted to the frame in 5 locations.

 

 

The total cost for the project must be under $1000

 

 

 

Yes

Excluding the cost of a new engine and labor for welding, the gasifier cost approximately $500.  Though our total cost is approximately $1000, we believe we could recreate this project, provided with a working go-kart and welding knowledge (and equipment) for less than $500.

 


 

Final Results

 

Our gasifier worked as anticipated.  However, a second prototype would include multiple upgrades over old systems.  First, the simple downdraft design would be improved to include a more traditional, yet complicated, Imbert design.  This would prevent the charcoal region from expanding up the fire tube and producing tarry fuel.  Second, the two filters, especially the inline filter, need to be more efficient.  Protecting the engine from tars would drastically improve longevity of the vehicle.  Lastly, the overall flow rate into the gasifier must be improved.  A larger flow rate will greatly improve the performance of the engine, providing it with more power and the ability to run at lower rpms.

 


 

Acknowledgements

 

Professors Kipp Bradford and Jerry Daniels

Brian Corkum

Indrek Kulaots

Charles Vickers, Jr.

Sean Bagge

 


 

Views:  

 


 

Comments (0)

You don't have permission to comment on this page.