EFFECT OF IGNITION TIMING ON
THE PERFORMANCE OF LPG
FUELLED SI ENGINE
R.M.Dabhadkar
Tiwari Chowk,Yavatmal rahuldabhadkar@gmail.com
Roshan J Pardhi
Jamankar nagar Yavatmal roshan.pardhi@gmail.com DEPARTMENT OF MECHANICAL
Abstract:
Fast depletion of fossil fuels and their detrimental effect on the environment is demanding an urgent need of alternative fuels for meeting sustainable energy demand with minimum environmental impact. A lot of research is being carried out throughout the world to evaluate the performance, exhaust emission and combustion characteristics of the existing engines using several alternative fuels such as hydrogen, compressed natural gas, alcohols, liquefied petroleum gas (LPG), biogas, producer gas, bio-diesels developed from vegetable oils, and others (Roy et. al, 2010). LPG and CNG are the alternative fuels to be widely adopted for use in the world. Gaseous fuel mix uniformly with air which burns precisely during combustion than liquid fuels. It has minimum carbon deposition & negligible physical delay. Internal combustion engines running on liquid petroleum gas (LPG) are well-proven technologies and work much like gasoline-powered spark-ignition engines. They are normally used as spark-ignition engines for bi-fuelled (gasoline/CH4) cars, but have also been used, for example, in compression-ignition engines for heavy-duty vehicles. Both LPG and NG are not used alone, but always in bi-fuel vehicles, in combination with gasoline. In bi-fuel vehicles two fuels are stored in separate tanks and the engine runs on one fuel at a time. Bi-fuel vehicles have the capability to switch back and forth from gasoline to the other fuel, manually or automatically. As a fuel for spark-ignition engines LPG have some advantages over gasoline, such as a better anti-knock characteristic and reduced CO and unburned HC emissions (Hsieh et al., 2002). Environmental point of view is that there is an increasing interest among the suppliers to investigate LPG as a transportation fuel. It was found that the liquid petroleum gas, roughly a mixture of propane and butane, which gives a benefit in terms of toxic hydrocarbons emissions and ozone formation due to its composition and CO2 emission levels (Heffel, 2003).
1. INTRODUCTION
Continuously decreased in reserve of fossil fuels, foreign exchange expenditure for import of crude petroleum, the unsteadiness of their prices and the increasingly stricter exhaust emission legislation, put forward the alternative fuels as substitute for the vehicles. The growing sector of transport, rise a big alarm for the day by day increasing number of vehicles and for the sensible contribution to the degradation of air quality in urban areas, as well as global pollution. Due to high thermal efficiency and power density, IC engine exhaust emission is been increasing, due to stringent emission norms caused engine manufacturer to examine the potential of alternative fuels. The research on alternative fuels has become essential due to depletion of petroleum products and its major contribution for pollutants. Sustaining a clean environment has become an important issue in an industrialized society.
Fast depletion of fossil fuels and their detrimental effect on the environment is demanding an urgent need of alternative fuels for meeting sustainable energy demand with minimum environmental impact. A lot of research is being carried out throughout the world to evaluate the performance, exhaust emission and combustion characteristics of the existing engines using several alternative fuels such as hydrogen, compressed natural gas, alcohols, liquefied petroleum gas (LPG), biogas, producer gas, bio-diesels developed from vegetable oils, and others (Roy et. al, 2010). LPG and CNG are the alternative fuels to be widely adopted for use in the world.
alone, but always in bi-fuel vehicles, in combination with gasoline. In bi-fuel vehicles two fuels are stored in separate tanks and the engine runs on one fuel at a time. Bi-fuel vehicles have the capability to switch back and forth from gasoline to the other fuel, manually or automatically.
As a fuel for spark-ignition engines LPG have some advantages over gasoline, such as a better anti-knock characteristic and reduced CO and unburned HC emissions (Hsieh et al., 2002). Environmental point of view is that there is an increasing interest among the suppliers to investigate LPG as a transportation fuel. It was found that the liquid petroleum gas, roughly a mixture of propane and butane, which gives a benefit in terms of toxic hydrocarbons emissions and ozone formation due to its composition and CO2 emission levels (Heffel, 2003).
LPG is stored as a liquid in a separate steel or composite vessel at the pressure of 10 bar, although it can stand a pressure of 20-30 bar. LPG supply to the engine is controlled by a regulator or vaporizer, which converts the LPG to a vapour. The vapour is fed to a mixer located near the intake manifold, where it is metered and mixed with filtered air before being drawn into the combustion chamber where it is burned to produce power, just like gasoline.
The LPG energy content (High Heating Value, HHV) is 46.23 MJ/kg. The high octane rating and the low carbon and oil contamination characteristics of LPG result in a documented longer engine lifetime, up to twice that of the gasoline engines. Because the fuel mixture is fully gaseous, cold start problems associated with liquid fuel are eliminated. LPG has relatively high energy content per unit of mass, the range of LPG vehicles is equivalent to that of petrol vehicles.
The ignition processes strongly affect the overall performance in spark ignition engines. Thermal efficiency and the level of NOx emission are strongly influenced by ignition timing. Proper ignition timing can offer high engine thermal efficiency, low levels of NOx emission and longer engine operational life. Knowledge of the ignition timing and the residence time are required before simulating any spark ignition engine design, where improper ignition timing can lead to misfire or knock and high level of cycle-to-cycle variation.
2. LITERATURE REVIEW
F. N. Alasfour [01]Investigated effect of varying ignition timing on NOx emission, exhaust temperature, knock occurrence and thermal efficiency in a spark ignition engine. A Hydra single-cylinder, spark-ignition, fuel injection engine was used with a 30% Iso butanol gasoline blend as fuel. Results show that retarding ignition timing causes the exhaust temperature to increase. For a lean mixture, advancing ignition timing has a great effect on the increase of the level of NOx, while for a rich mixture advancing ignition timing has a minimal effect.
O.Badr, N.Alsayed and M. Manaf [02] Presents the experimental results of a parametric study on lean operational limits of Ricardo E6 Engine using propane and LPG as a fuel. The result had shown that the spark timing have a significant influence on engine lean limit, the research has taken out the results for only first misfire criteria for two speeds only. They had not measured the exhaust emissions and certain other parameter.
Tolga Topgul, Huseyin Serdar Yucesu [03]Carried out the performance and exhaust emission investigation on Hydra single cylinder, four stroke S.I engineusing unleaded gasoline (E0) and unleaded gasoline ethanol blends (E10, E20 E40 and E60). By varying the compression ratio (8:1, 9:1 and 10:1) and ignition timing at a constant speed of 2000 rpm at wide open throttle (WOT). The experimental results showed that blending slightly increased the brake torque and decreased carbon monoxide (CO) and hydrocarbon (HC) emissions.
Hyungseuk Ohn, Seongeun [04] had done the investigation to obtain a better understanding of THC (Total hydrocarbon) emission characteristics during engine restart and deceleration driving on a HEV power train of a parallel motor/generator type. The experimental conditions cover variations of the high voltage battery state of charge (SoC), spark ignition timing and injected fuel mass. Result showed that the effect of the spark timing control was slight, but the reasonable injection duration for stable combustion was more than 7 ms at the first cycle shortly after engine start-up, although the injection rate was 2.7–3 ms in the idle state.
Idris Cesur [05]Showedthe effect of modified ignition timing of an LPG fuelled spark ignition engine on cold start Hydrocarbon emission (HC) at the wide open throttle (WOT) conditions. The engine was tested at the variable ignition timing.Cold start HC emission by using thermal barrier layer (TBL) piston was found to be reduced. In the case of using TBL piston and variable ignition timing, at the high engine speed the engine torque and brake power have been increased as 15% at the 2700 rpm.
Jiwak Suryawanshi and Pravin Nitnaware [07]Showed the researches on necessary modification and timing variation of engine for safety and backfire, The test was carried on 1 cyl.,173cc,air cooled, 4 stroke engine developing power of 4.4 KW @5500 RPM on CNG and 6 KW @5000 RPM on gasoline. To avoid back fire spark timing was retarded and gas power valve was adjusted for lean mixture operation. Under uniform test condition, hydrogen 3 wheeler showed a fuel efficiency of 138km/kg, in comparison to 38 km/kg in CNG and 25km/l on gasoline. Fuel efficiency in terms of gasoline liter equivalent (GLE) on net energy basis, hydrogen operation has substantially higher energy efficiency (36.4 Km/GLE), 1.3 times the CNG (28.7 km/GLE) and 1.4 times the gasoline operations (25.3km/lit).
E. Ramjee and V. K. Reddy [08] Had done the research on alternative fuels and showed its need as it had become essential due to depletion of petroleum products and its major contribution for pollutants, They had compared effect of CNG on performance of engine and its emissions.
ETSAP [09] Had showed the advantage of using LPG as a fuel in Bi-fuel mode and showing its cost effectiveness and clearly mentioned the present status of LPG as a fuel and its growing demand worldwide. 3. PROBLEM DEFINATION
By studying the researches done on spark timing variation, it is observed that certain researches are been carried on variation in spark timing using fuels like alcohols gasoline blends, CH4/H2 mixture, gasoline, CNG etc, these researches are been done depending upon certain parameters like cold starting, WOT position, TBL coated piston, lean limit, first misfire condition & knocking tendency only. As we know that LPG is good alternative fuel to gasoline fuel certain researches is to be carried out based upon different parameters using LPG as a fuel.
As most of the LPG vehicles are conversions from petrol vehicles. Many cars makers offer conversion/bi-mode vehicles. LPG technology is rather popular in European union, Australia, India and some other countries, and its popularities is been increasing day by day because of fuel crises and proving best as a alternative fuel, To satisfy the need for good performance and less pollution emission using LPG as a fuel researches are still to be done depending upon spark timing. As we know there is variation in performance and emission of engine by changing spark advancement and retardation. The detail study of above mentioned parameters and certain other parameters using LPG as a fuel is to be done.
4. AIM AND OBJECTIVE
EFFECT OF IGNITION TIMING ON THE PERFORMANCE OF LPG FUELLED SI ENGINE.
The proposed work is to study effect of ignition timing on LPG fuelled S.I Engine. The objectives which are to be carried out are:
1. To study effect of ignition timing on performance of Engine. 2. To study the effect of ignition timing on exhaust emission.
5. METHODOLOGY
Correct setting of the ignition timing is vital for the engine to produce the maximum amount of power possible by converting the combustion forces generated in the cylinder into movement of the crankshaft. Any inaccuracies will diminish the amount of usable power produced and increase the amount of wasted heat fed into the structure of the engine. Correct setting of the ignition timing is one of the key factors in achieving reliable starting and efficient running.
Spark timing setting can be done with respect to different spark mechanism used in the engine, some of the methods are been discussed, Spark timing can be varied by rotating the contact breaker base plate with respect to the ignition cam or vice versa. The contact breaker base plate carries the contact breaker lever arm. A timing lever is clamped around the distributor body mounting shank by means of a screw. With the help of the timing lever, the whole distributor body can be rotated to some extent on its seating, by this way spark timing can be varied, The spark timing can be varied either manually or automatically. Automatic timing control includes two types:
a) Vaccum advance mechanism: Also known as load retard timing unit. It adjusts spark timing according
to load condition i.e. according to charge density condition. This unit advances the spark timing as the charge density decreases and retards the timing as the charge density increase. A spring mechanism is in this system which moves the breaker plate accordingly and whose setting can be varied to get change in spark timing.
consisting of ignition cam, advance cam, governor pair, two springs and plate attached to distributor shaft. Advance cam is operated by the governor weights. When the engine is speeded up the weights swing out alternately rotates or advances the advance cam. This relative movement of the ignition cam with respect to the distributor shaft causes the ignition cam to separate the breaker point. This method is therefore mostly used for advancing mechanism. The combined mechanism of the above given mechanism is also been used for advancing mechanism.
Some of the more manual methods which are used for spark timing tuning is been used, one of the method used for tuning of BSA M20 model is been explained. The basics apply to all makes, after taking into account the different setting that may be required and physical differences between engines types, we will assume Mag/dyno unit fitted in this example for first time. Firstly with the mag/dyno off the engine set the maximum point’s gap to the correct figure (.012”). To do this turn the armature until the points are on the high point of the contact breaker cam and are fully open. Then using the correct mag spanners and a .012” feeler gauge slacken the fixed contact breaker locknut, adjust the contact to give the correct gap (.012”) and retighten the locknut. The mag/dyno can now be fitted to the mag platform, taking care to position the four locating pegs in the mag base correctly in the slots machined into the platform.
Setting the ignition timing:
The correct position for the piston (BSA M20) is 7/16” before top dead centre on the compression stroke ie. with both valves fully closed and the tappet heads free to rotate. The piston should be flush with the top face of the cylinder in this position but if it is below the top face this distance must be measured (in thousandths of an inch) using a depth micrometer or clock gauge and the figure noted. If the piston was flush with the top face of the cylinder now set the depth micrometer to 7/16” (.437”). If the piston was, for example .010” below the top face of the cylinder add that amount to the setting. Using the example above the final setting would thus be .447”.
Fig. Preparation before setting the timing
text turn the engine in the opposite direction to normal running (viewed from the timing side turn the engine anti clockwise) until the piston is approx. 3/4 of the way down the stroke. Place the depth micrometer onto the top face of the cylinder with the shaft protruding into the cylinder. Now slowly turn the engine in the direction of normal running (viewed from the timing side turn the engine clockwise) until the crown of the piston just contacts the depth micrometer. The piston position is now set. The magneto must now be set in the correct position. Timing is set on most machines with the magneto contact breaker cam in the fully advanced position. This can cause some confusion as the design of the magneto was changed post war and a magneto of either type could be fitted. The simple way to determine which type is fitted is from the position in which the adv/rtd cable enters the mag body. Viewing the mag from the contact breaker end, if the cable enters to the right of the contact breaker assembly the contact breaker cam is set fully advanced when the cable is pulled tight by the handlebar adv/rtd lever. If the cable enters the mag to the left of the contact breaker assembly the contact breaker cam is set fully advanced when the cable is slack. Having determined which type is fitted set the contact breaker cam in the fully advanced position with a ‘slack’ or ‘tight’ cable as appropriate.
direction of normal running until the piston is at the beginning of the compression stroke (with both valves closed and the tappets free to rotate). Now insert the rod through the timing hole in the head but DO NOT release it. Continue to slowly turn the engine. As the piston rises towards top dead centre it will come into contact with the end of the rod which will begin to rise with the piston. As the piston reaches top dead centre (the top of its stroke) the movement will stop momentarily before the piston starts to fall again. The aim is to stop rotating the engine exactly when this momentary ‘pause point’ is reached.Once the ‘pause point’ has been correctly set, sight across the boss that the bolt sits on when fitted and using a sharp scriber make a mark on the rod. This is the top dead centre mark. Now remove the rod and using the scriber and a steel engineers rule carefully scribe another mark 7/16” above the tdc mark. Make this measurement as accurately as possible. Following the procedures previously described turn the engine backwards to the starting point, insert the rod and slowly turn the engine forwards again. As the piston (and rod) rise sight across the timing bolt boss and watch carefully for the (7/16”) mark on the rod to emerge and line up with the boss. When this occurs the piston will be set at 7/16” before the top of the stroke. Having previously set the mag position the mag drive gear can now be refitted as previously described. After fitting check that the contact breaker opening point and the (7/16”) mark scribed on the rod are both in the correct positions at the same time. If the engine is fitted using either of the timing methods described it is a good idea to select a high gear and ‘jog’ the back wheel to turn the engine either backwards or forwards as required when making piston position settings.
6. EFFECT OF ADVANCING OR RETARDING IGNITION TIMING
Ignition timing i.e. crank angle at which spark occurs with respect to TDC has a significant effect on engine performance. Too early timing increases the peak pressure and raises the expansion curve above that for optimum timing. Sometime this timing cause abnormal combustion called knock. Too late timing lowers peak pressure and also raises the expansion line above that for optimum timing. Both too early and too late timings lower engine efficiency. The optimum spark advance is one which will cause half the pressure rise at the dead center. Maximum brake torque [MBT] timing depends on the speed and as speed increases the spark must be advanced to maintain optimum timing, because the duration of combustion process in crank angle degrees increases, optimum spark timing also depends on load. As load and intake manifold pressure changes, The spark timing must be changed to maintain optimum engine performance. Thus, the determination of accurate MBT timing is difficult but it is important because NO and HC emission vary significantly with spark timing.
If the spark is advanced too much, combustion will get completed before the piston reaches the end of its compression stroke. This will result in excessive combustion pressures. Then the crankshaft and connecting rod must force the piston upward against the combustion pressure. This will result in a large negative work at the end of the compression stroke. Consequently there will be reduction in the net work output and efficiency of the engine. Too late spark timing lowers the peak pressure and the efficiency. With late spark timing much of the heat will be passed into the cylinder block, cylinder head and exhaust system instead of being used to power the engine. Late ignition timing can cause an engine to overheat so that exhaust manifold may crack. The exhaust emissionsalso vary as change with respect to spark timing.
7. REFERENCES
[1] F. N. Alasfour “Nox Emission From A Spark Ignition Engine Using 30% Iso-Butanol–Gasoline Blend: Part 2 Ignition Timing” Mechanical Engineering, Kuwait University, P.O. Box 5969, Safat, 13060 Kuwait,15 September 1997.
[2] O.Badr, N.Alsayed and M. Manaf, “A Parametric Study on Lean Misfiring and Knocking Limits of gas fueled spark ignition Engines” College of Engineering, United Arab Emirates University, P.O. Box 17555, Al-Ain, Abu Dhabi, United Arab Emirates, March 1997. [3] Tolga Topgu, Huseyin Serdar Yucesu, Can Cinar, Atilla Koca “The effects of ethanol–unleaded gasoline blends and ignition timing on
engine performance and exhaust emissions” Faculty of Technical Education, Department of Mechanical Education, Gazi University, Besevler, 06500 Ankara, Turkey, March 2006.
[4] Hyungseuk Ohn, Seongeun Yu, Kyoungdoug Min “ Spark timing and fuel injection strategy for combustion stability on HEV powertrain” School of Mechanical & Aerospace Engineering, Seoul National University, Seoul, Republic of Korea, April 2010 [5] Idris Cesur “The effects of modified ignition timing on cold start HC emissions and WOT performance of an LPG fuelled SI engine
with thermal barrier layer coated piston” Technical Education Faculty, Sakarya University, Sakarya, Turkey, January, 2011
[6] Mehmet Bayrak, Bilge Albayrak Çeper, Nafiz Kahraman, Selahaddin Orhan Akansu “Expermental Study Of Ch4/H2 Mixtures-Lpg-Gasoline In Internal Combustion Engines”Dept. of Mechanical Engineering, Erciyes University Engineering Faculty, Kayseri, Turkiye, 2011.
[7] Jiwak G. Suryawanshi & Pravin T. Nitnaware “An Investigation On S.I Engine Using Hydrogen And CNG Blends” Department of Mechanical Engineering,Visvesvaraya National Institute of Technology, Nagpur & D.Y. Patil College of Engineering, Pune, June2011.
[8] E. Ramjee and K. Vijaya Kumar Reddy “ Performance analysis of a 4-stroke SI engine using CNG as an alternative fuel” Department of Mechanical Engineering, NTUH College of Engineering, Hyderabad, July 2011
[9] Energy Technology Systems Analysis Programme (ETSAP)- Technology Brief T03-April2010- www.etsap.org [10] The BG Tuning Manual.
[11] Eric Tribbett ,Ed Froehlich ,Lex Bayer “Effects of Ignition Timing, Equivalence Ratio and Compression Ratio on RDH Engine Performance”Mechanical Engineering Dept. Stanford University,
[12] Heywood J.B, Internal combustion engine fundamentals, McGraw Hill Book Co., USA. 1995.
