6. Lean Burn Combustion Engine

LEAN BURN COMBUSTION ENGINE USING

CATALYTIC COATINGS

Presented By

M.Ganesh Karthikeyan D.Ramesh Kumar(B.E.AUTOMOBILE, IRTT, ERODE)

Email ID: [email protected] [email protected]

Contact Address: M.Ganesh karthikeyanG-27, IRTT Hostels, Final YearInstitute of Road & Transport Tech,Erode 638 316.

Ring me: 98947 97196 99944 27507

ABSTRACT

The lean combustion of an SI engine has been recognized as one of the most promising method of further improvement of fuel economy. According to automotive pollution point of view, exhaust emissions as NOx, CO &HC are reduced because of abundance of oxygen and lowering of peak temperature.

The present study was aimed at ascertaining the benefits of employing catalysts in the combustion chamber of an SI engine. In our study we have tried to combine the concept of catalytic coating and lean burn to improve performance of an SI engine. The literature study has revealed that there is enormous potential for catalytic coatings in the automotive engines.

We have chosen 150CC BAJAJ scooter engine in our study because these two stroke engines are one of the greatest monsters that could demolish the atmosphere. In our investigation we have used a silver catalyst and nickel catalyst in 150CC engine. Experiments were conducted using state-of-the-art instrumentation comprising of PC based engine combustion analyzer equipment and exhaust analyzer.

As the result of coating of catalysts such as nickel and silver the Brake thermal efficiency of the engine has been increased by nearly 10% to 30% The result also indicates the reduction of,

70% to 90% of CO 10% to 20% of HC & 15% to 25% of fuel consumption.

INTRODUCTION

Due to the increasing cost and uncertained supply of petroleum in recent years, there have been strenuous effects to make spark ignition and compression engines more efficient. One of the most promising methods as far as SI engines are concerned is the lean burn engine. The concept of internal combustion engine is one, where oxidation of fuel is brought with the aid of a catalyst in the combustion chamber walls offers the advantages of a stratified charge engine without its disadvantages. The benefits which could be obtained from homogeneous lean mixture burning in a spark-ignited engine are well known. Equally known are the potential difficulties encountered with lean combustion, cyclic variation etc. However, if these above difficulties are overcome, then the benefits that can be obtained are high thermal efficiency and lower exhaust emissions.

There are several methods adopted to burn the lean mixture efficiently. Recently use of catalysts in the combustion chamber is being investigated to improve the combustion process by increased chemical activity of the charge prior to ignition.

The catalyst are used in the form of coating on the walls or in any form to initiate combustion and make it burn faster, then the advantage improved efficiency can be obtained in addition to lower exhaust emissions.

This new concept of catalytic activation of the charge for lean combustion has been tried in this work and its effect on the combustion process has been investigated. The influence of various catalysts such as silver and nickel are determined.

OBJECTIVE OF THIS PAPER

To develop a new type of combustion chamber, called catalytic combustion chamber in order to make the combustion of lean mixture faster.

To modify the existing combustion chamber suitable for fast burning of lean mixtures.

To obtained increased efficiency and lower exhaust emissions. To investigate the combustion characteristics of lean mixtures so that it could

be employed later on in the existing engines with minimum modifications at a lower cost.

ADVANTAGES OF LEAN BURN MIXTURE

Theoretically the energy efficiency of the engine becomes greater. Exhaust emissions such as CO, HC are lower when the mixture is made

leaner. Knocking in the engine is reduced to greater extent. The ratio of specific heats approaches that of the air with lean mixture. Dissociation losses are reduced because of lower combustion temperature. Heat transfer losses to cooling medium are reduced because of lower peak

temperature.

CONCEPT OF CATALYTIC COMBUSTION THE CATALYST: Any discussion of catalyst combustion would not be complete without some methods of catalyst. First of all, the catalyst must be capable of withstanding continues and cyclic operation at very high temperatures, ideally as high as 1600’C, without degradation of either catalyst or physical properties. This requires the use of high melting point materials with good thermal shock properties; the catalyst must have a low intrinsic pressure drop. Finally, the catalyst activity must be high enough to permit catalyst ignition at reasonably low temperatures. This facilitates rapid reliable light of and stable operation. The catalytic ignition temperature of course depends not only catalyst activity but on either factor such as fuel concentration and flow velocity. Combustor catalyst have been operate at temperature over 1650’C without loss of low- temperature activity long- term testing of high temperature catalysts is needed. With the discovery that heterogeneous catalyst can be used to promote stable ultra lean thermal combustion at heat release comparable to those of conventional combustors. It as become feasible to consider catalytic system for replacement of conventional combustor. In the catalytic combustor, homogeneous thermal combustion occurring in parallel with heterogeneous reactions at the catalyst valve is inducted by a hot boundary layer, fixed in space by the catalytic surface. This mode of operation gives the catalytic combustor the potential of operational stability far superior to that of any offer other type of combustor. Catalytic surface reactions result in catalyst temperatures approximately equal to the local adiabatic flame temperature. The main aspects of catalytic theory are when a gaseous fluid passé over a catalyst surface and reacts on the surface the heat liberated in transferred back into the gas phase under adiabatic steady- state conditions, the rate of

heat transfer catalytic channels, thereby imposing significant pumping losses. These approaches also relieved on complicated scavenging and flow delivery system.

NICKEL AND SILVER METAL CATALYST IN THE COMBUSTION CHAMBER: The use of nickel and silver catalyst in the combustion chamber of an internal combustion engine that operates with lean burn concept offers an opportunity to develop an engine emits particularly low level of HC, CO &improved fuel economy.

CONCEPT OF CATALYTIC PRECHAMBER:A catalytic prechamber is attractive from the stand –point of

controlling all phase of in-cylinder combustion. Such a prechamber influences both chemical and gas dynamic processes. It regulates contact between the fresh charge and the catalytic surface it allows activation to take place in a well-defined volume adjacent to the ignition sources. It provides a means of independently adjusting the catalytic surface temperature, and it acts a turbulence generation pot, which intensifies burning o0f the non-activated portions of the charge.

CONCEPT OF CATALYTIC COATED ENGINE A catalytic engine is an internal combustion engine where the heat release is brought about by the use of a catalyst. This definition includes engines where the combustion is commenced sustained or aided by the action of a catalyst on the air/fuel mixture.

ROLE OF COMPRESSION RATIO: The compression ratio of all internal combustion engines directly affects the fuel economy. The compression ratio of the petrol engine cannot be raised too much because of the tendency of the engine to knock. This is a result of premature spontaneous combustion in the unburnt portion of the charge ahead of the flame front and brought about by the use of fuel with too low octane number; the octane number being a measure of the fuel’s resistance to knock in the spark ignition engine. Ignition of the charge before the spark timing is also a problem under these circumstances. It has been shown that as the compression ratio of the petrol engine is increase so its economy increases. In our paper compression ratio was slightly increased by the catalyst coating.

THE NEW CONCEPT: There is therefore a need for a method of combustion, which would enable very lean mixtures to be efficiently oxidized, and operate in an internal combustion engine at the compression ratio of about 12:1. The concept of the charge is passed through a catalyst; oxidation can occur even at low temperature and very lean mixtures. Thus all the fuel should be oxidized and the engine can run unthrottled which should give economy. The formation of HC and CO in the combustion chamber is also strongly dependent on the air/fuel ratio, and lean operation gives reduced emissions of these pollutants in the exhaust of the engine. The catalyst enables oxidation of HC at much lower temperature normally possible. So these emissions are also reduced. Another

important advantage of the catalytic engine concept is that it is capable of operating on many different liquid fuels.

SECTION OF CYLINDER HEAD AND PISTON SHOWINGTHE PRESSURE TRANSDUCER, SPARK PLUG AND COATING

COATING DETAILSSELECTION OF COATING MATERIALS: The various surface properties that can be enhanced by the proper selection of coating materials are,

Mechanical properties. Thermo chemical properties. Electrochemical properties. Optical properties. Electrical properties. Etc.,

Selection of a specific coating is largely dependent on the surface properties demanded by a particular application. The selection of the coating is generally not influenced by the base material on which it is to coated. All elements that do not decomposed at high temperatures can be coated by a thermal spraying including metals, ceramics, cements, intermetallic, etc.,

Given the large variety of sprayable materials, aside choice of feedstock powders is normally available for obtaining a desired functional attribute. The choice specific powder material is governed by the operating conditions of the coated components as well as by the economic constraints.

ELECTROPLATING COATING TECHNIQUES: Since the base metal on which the coating applied was alloy aluminum, a preconditioning of the surface was necessary and it was done by a process called zinc coating to remove oxide layer to enable the coating to have good bonding with base metal. After conditioning of piston and cylinder head, electroplate coating was done

SETUP FOR ELECTROPLATING OF CATALYSTON THE PISTON CROWN

MODIFICATIONS IN THE ENGINE

The following modifications were made to the engine for the lean combustion of commercially available gasoline with the carburetion and spark ignition.

The cylinder heads and pistons were nickel and silver coated A pressure transducer for measuring the pressure was mounted on the cylinder

head. A modified carburetor for varying air fuel ratio is mounted to engine. A crank angle degree marker (CDM) is coupled to the engine crankshaft to

measure the crank angle. An air box to find the air fuel ratio. Modems to interface the engine and the computer. An eddy dynamometer is coupled to the engine crankshaft to load the engine. A fuel flow meter to measure the fuel flow rate.

MODIFICATION IN THE CARBURETTOR

Conventional carburettor is modified to obtain different A/F ratio. In order to obtain a lean mixture the fuel quantity that is inducted into the mixing chamber should be reduced. For that the main petrol jet should be a variable delivering unit. But in conventional carburettor the quantity of air and fuel is varied simultaneously so that constant air fuel ratio is admitted to the engine. In the conventional carburettor, a slider is used to control the air and a spindle, which is attached to the slider, is used for controlling the fuel flow. In the modified carburettor, fuel flow rate is controlled by a separate spindle. This spindle is threaded to cap of the carburettor and it as a conical section at the other end. The conical can be moved in the fuel control valve; so that the opening area of the valve can be controlled which in turn controls the quantity of fuel admitting into the mixing chamber. The accelerator cable is attached to the slider, which controls only the air. Thus we obtain a different air-fuel ratio at different positions of the spindle.

SECTION VIEW FOR MODIFIED CARBURETTOR

MODIFIED CARBURETTOR

SPECIAL EQUIPMENTS The list of various special equipment used in this steady are _

Pressure Transducer.Crank degree marker (CDM)Eddy current dynamometer.Digital tachometer.Exhaust gas analyzer.Automatic fuel flow meter.Avl indimeter software.

CRANK ANGLE DEGREE MARKER (CDM)

The angle encoder 364 is a high precision optical encoder for angle – related indicating measurements and rotary oscillation analyses in internal combustion

engine. The high rigidity of the angle encoder 364 has been tested in particular on high - speed-racing engines. The angle encoder364 accurately responds to each speed variation of the engine and it is ideally suited for dynamic measurements and start investigations. The encoder has been developed for highest mechanical load. It can be flanged directly to the engine and therefore guarantees most precise measurement results. Measuring errors resulting from flexible shafts or relative movements between encoder and engine are thus eliminated. It is compact and light- weight in design to keep the additional mass forces on the crankshaft of small engines as low as possible.

EXPERIMENTAL SETUP

The experimental setup consists of an engine and all the latest equipments and accessories required for measuring the engine parameters. The engine used is a BAJAJ 150CC engine, which is mounted on a concrete bed to withstand the dynamic forces and vibrations produced. The engine uses a BINK carburettor for high efficiency and performance.

Air is admitted into the engine by means of an indigenously designed air- box, also known as air- damper. It is used to measure the volume of air consumed by the engine and as a pressure damper. The air-box houses an orifice plate.

Admission of fuel into the engine done by means of fuel reservoir. The fuel flow measurement in the fuel reservoir has two photoelectric cells, which are used to measure the time taken for consumption of 25CC and 754CC fuel respectively. The air –fuel ratio of the engine is calculated using the pressure drop across orifice plate and time taken for fuel consumption.

Loading of the engine is done by means of an eddy current dynamometer. The dynamometer shaft is directly coupled to the engine gearbox shaft and thus the engine can be loaded in constant torque, constant speed and constant current modes. A pump is used to pump water to cool the dynamometer while taking higher loads. The load on the engine, speed of the dynamometer shaft and time taken for fuel consumption are all displayed on an electronically controlled, power operated dynamometer control panel.

One more highlight of this setup is the crank degree marker. It is an accurate device, which is directly coupled to the engine crankshaft and is used for measuring the crank angle at which maximum pressure occurs. The CDM also measures the heat release at various crank angles.

The setup also has provisions for measuring the exhaust emissions. The exhaust gas from the engine is fed into a moisture separator, which separates the moisture from the exhaust and then feeds into the exhaust gas analyzer. The EGA measures the CO emissions in % of volume and HC emissions in ppm.

SECTIONAL VIEW OF EXPERIMENTAL SETUP

CONCLUSIONS

Brake thermal efficiency as improved in both nickel and silver coatings by nearly 10% to 30%.

Good combustion characteristics indicate an ability to use lean air –fuel ratio.

In case of exhaust temperature coated engine as the least.

The benefits of using lean mixtures in S.I. engines are obvious. Better fuel utilization and lower exhaust emissions are achieved. However, some loss of heat power output has to be accepted. Catalytic treatment of exhaust gases also can pose problems due to the low temperature of exhaust gas.

The result indicates reduction of about 70% to 90% of CO and 10% to 20% of HC and 15% to 25% of fuel consumption.