EFFECT OF CYLINDER HEAD GASKET ADDITION AND VARYING OCTANE NUMBER GASOLINE TO INTERNAL COMBUSTION ENGINE PERFORMANCE

The aim of this research was to investigate the different impacts of compression pressure on power and torque outputs using gasoline RON 92, RON 95


INTRODUCTION
The conversion of thermal energy into mechanical energy carried out by an internal combustion engine, where a series of devices convert heat energy into kinetic energy [1].Several factors affected the performance of an internal combustion engine, including the quality of the fuel used and the compression pressure in the engine.Usage of low-quality fuel in an engine with large compression would resulted in decreased engine performance and increased fuel consumption [2].Internal combustion engines commonly used in motorcycles and cars have cylinder component with a piston that moves back and forth [3].A four-stroke engine required two revolutions of the crankshaft, In other words, each cylinder requires the piston to go through four strokes to complete one cycle within the cylinder [4].
The performance of an engine depended on the efficiency of fuel and air mixture combustion inside the cylinder.In engines with large compression and high-quality fuel, the result is the most efficient engine performance [5].Information from the Indonesian Motorcycle Industry Association (AISI) data shown that domestic motorcycle sales increased in 2021, reaching a total of 5,057,516 units sold, which is an increase of approximately 38.2% compared to the previous year.Motorized vehicles were the largest consumers of fuel in the transportation sector, especially those using gasoline [6].Currently, there are several gasoline suppliers, both government and private companies, offering several fuel variants.Gasoline categories are grouped based on the Research Octane Number (RON).Some RON values found in gasoline in Indonesia include RON 90, RON 92, RON 95, RON 98 and even RON 100 [7].
The effect of increased the fuel octane number is to shorten the combustion duration and reduce the likelihood of detonation [8].The research conducted by Rodríguez-Fernández and colleagues with the title "Enhancing fuel economy and vehicle performance through higher octane-rated gasoline" found that using higher octane number fuel significantly increases the power generated by the vehicle and shortens acceleration time.Additionally, using higher-octane fuel is also effective in reducing vehicle exhaust emissions due to reduced fuel consumption [9].Bi and colleagues found that detonation (knocking) in engines reduces thermal efficiency and limits the improvement of gasoline engine performance.Detecting the characteristics of engine detonation, including mild detonation, were crucial for controlling engine detonation.The use of higheroctane fuel can reduce the effects of detonation and improve thermal efficiency in gasoline engines [10].
Knocking referred to the sound or waves associated with the spontaneous ignition of a portion of the air-fuel mixture before the flame from the spark plug ignition [11].When detonation occurs, there are highfrequency pressure oscillations that could be observed [12].Detonation has the potential to cause several forms of damage, including piston crown melting, piston ring sticking, and cylinder head gasket leaks [13].The findings of the research conducted by Jiang and colleagues indicate that to achieve high power efficiency and reduce Nitrogen Oxide (NOx) emissions in internal combustion engines, adjustments to the Exhaust Gas Recirculation (EGR) components are necessary, as well as selecting fuel with an appropriate octane number.The choice of fuel with the right octane number plays a crucial role in achieving optimal power output and maintaining low levels of exhaust emissions [14].
The study conducted by Zhang and colleagues reported that increasing the compression ratio in an engine can effectively reduce fuel consumption [15].Increasing the compression ratio would also elevate the combustion temperature inside the cylinder, and the extent of the impact from different mechanisms varies with different compression ratios, resulting in a decrease in HC emissions when the compression ratio is increased [16].The use of fuel supplemented with methyl ester in high compression engines would enhance performance and actively reduced emissions of Nitrogen Oxide (NOx) and Carbon Dioxide (CO2) gases [17].
Jurnal Media Mesin, Vol. 25 No. 1 Printed ISSN: 1411-4348 Online ISSN: 2541-4577 Today, automotive manufacturers have been producing high compression engines to enhance performance, both in motorcycles and cars.However, there is low consumer awareness about the need for high-octane fuel to achieve optimal performance in high compression engines.This can be seen from recent statistics released by the Directorate General of Oil and Gas, which shown that The RON 90 gasoline continues to outsell RON 92 and 95 gasoline by a significant margin.. From this data, it can be concluded that many consumers still choose to use low-octane gasoline in their vehicles, even though these vehicles generally have large compression ratios [18].Based on the explanation above, we will conduct a performance test on a single-cylinder engine with two different compression ratios: 11.8 Kg/cm2 and 10 Kg/cm2.This test will use three different types of fuel: RON 92, RON 95 and RON 100 gasoline, with the aim of observing the differences in power and torque output.

METHODOLOGY
This research involves experiments using a 125 cm 3 single-cylinder motorcycle engine.The selection of this type of engine is based on the popularity of vehicles in Indonesia that use single-cylinder engines with a 125 cm 3 capacity.To adjust the compression pressure in the engine, gaskets are used on the cylinder head in two different variations: one gasket and three gaskets.Adding gaskets to the cylinder head results in a change in the combustion chamber volume, which affects the compression pressure value.Throughout the testing, the settings for the main jet, pilot jet, and the number of idle screw rotations on the carburetor are kept constant.Test data results are then analyzed directly to draw conclusions.Additionally, the test data will be presented in the form of graphs and tables to facilitate the reader's understanding.It is clearly seen in Table 1.

Table 1. Engine specification for testing
Engine type 4-stroke, SOHC Cylinder volume (cc) 124.8 Bore x Stroke (mm x mm) 52.4 x 57.9 Compression ratio 9.0 : 1 Fuel supply system Carburettor Ignition system Capacitor Discharge Ignition (CDI) The basic principle of a dynamometer is to measure the power, torque, or force generated by an engine or vehicle by measuring the forces generated by the engine or vehicle.The operation of a dynamometer involves applying a resistance load to the engine or vehicle being tested, and then measuring the reaction or force generated by the engine or vehicle in response to this load.In the context of engine performance testing, the dynamometer will record data on the torque produced by the engine at several engine speeds, and based on this data, it is processed to calculate the power generated by the engine at specific RPMs.This basic principle allows us to gain a more accurate understanding of the engine's characteristics.Engine performance can be measured using Equation (1), where (T) represents torque, (F) is the force applied to the rotor, and (r) is the distance used as a multiplication factor.
The power generated can be calculated using Equation (2), with N as the Crankshaft's rotational speed (Rpm).The performance test of the single-cylinder engine conducted using a dynamometer along with some additional equipment such as a toolset, measuring burette, and a stopwatch.The fuel specifications used in this test are indicated in Table 2. Before undergoing testing using the dynamometer, it is necessary to position the motorcycle precisely so that the rear wheel is directly over the dynamometer's roller.Next, it is important to connect the tachometer cable to the high-tension cable at the spark plug and disconnect the hose connected to the carburetor.Then, the hose from the measuring burette will replace the one leading to the carburetor.The measuring burette will then be filled alternately with RON 92, RON 95, and RON 100 fuel.The testing scheme with the dynamometer can be found in Figure 1.Once all preparations are completed, the performance test can be conducted by two Persons.One person will operate the dynamometer testing software, while the other person is responsible for operating the engine.

Torque output comparison
Torque testing has been conducted at different levels of compression pressure using RON 92, RON 95, and RON 100 gasoline.Table 3 displays the torque testing results for the engine using RON 92 fuel.Each torque value is obtained through three repeated tests, and the numbers listed in Table 3 represent the average values.In general, the engine exhibiting a compression pressure of 11.8 Kg/cm 2 demonstrated higher torque [19].Specifically, when operating at a compression pressure of 11.8 Kg/cm 2 , the engine produced a peak torque of 9.31 Nm within the engine speed range of 5000 RPM.In summary, the engine featuring a compression pressure of 11.8 Kg/cm 2 is capable of achieving a 7.3% increase in torque output compared to the engine with a compression pressure of 10 Kg/cm 2 .The torque output comparison across several compression pressure variations using RON 92 gasoline is visually represented in Figure 2. The outcomes of the engine torque tests utilizing RON 95 gasoline are outlined in Table 4.The highest recorded torque, reaching 9.61 Nm, was achieved when the engine operated at a compression pressure of 11.8 Kg/cm 2 within the engine speed range of 5000 RPM.In contrast, the engine featuring a compression pressure of 10 Kg/cm 2 yielded a lower torque output of 9.26 Nm during the same conditions.Overall, when fueled with RON 95, the engine operating at a compression pressure of 11.8 Kg/cm 2 exhibited higher torque compared to the engine with a compression pressure of 10 Kg/cm 2 .The lowest recorded torque output, at 4.07 Nm, was observed in the engine with a compression pressure of 10 Kg/cm 2 within the engine speed range of 8000 RPM.Meanwhile, within the identical engine speed range, the engine operating at a compression pressure of 11.8 Kg/cm 2 generated an additional 1.09 Nm of torque.This represents a 7.3% increase in torque output, with the engine at 11.8 Kg/cm 2 producing 8.16 Nm compared to the engine with a compression pressure of 10 Kg/cm 2 within the engine speed range of 6500 RPM.The engine with a compression of 11.8 Kg/cm2 demonstrated a higher torque output of 0.5 Nm at an engine speed of 5500 RPM and 0.66 Nm at 6000 RPM, respectively, in comparison to the engine with a compression pressure of 10 Kg/cm 2 [20].This trend indicates that the torque output increases with higher engine compression pressure.The torque variations among different compression pressures are visually depicted in Figure 3.

Figure 3. Engine torque output at several compression pressure using RON 95 fuel
Torque testing has been conducted on the engine with several compression pressure variations using RON 100 gasoline, and the results have been compiled in Table 5.Each torque value recorded in Table 5 represents the average result of three experiments.In general, the engine with the highest compression pressure, which is 11.8 Kg/cm 2 , tends to produce higher torque output at all engine speed [21].The engine operating at a compression pressure of 11.8 Kg/cm 2 attained its peak torque output of 9.93 Nm within the engine speed range of 5000 RPM.Within the identical engine speed range, the engine featuring a compression pressure of 10 Kg/cm 2 generated a lower torque, exhibiting a difference of approximately 0.96 Nm compared to the engine at 11.8 Kg/cm 2 .The torque comparison results for the engine with various compression pressure settings using RON 100 fuel are visually represented in Figure 4.The engine, running at a compression pressure of 10 Kg/cm 2 , recorded the lowest torque output at 4.18 Nm, specifically at an engine speed of 8000 RPM.Within the identical engine speed range of 8000 RPM, the engine operating at a compression pressure of 11.8 Kg/cm 2 exhibited a higher torque output, reaching 5.79 Nm.
In summary, the torque output recorded in the engine with a compression pressure of 11.8 Kg/cm2 is 17% higher compared to the torque output in the engine with a compression pressure of 10 Kg/cm2.The test results reiterate the importance of using fuel with a higher-octane number in engines with elevated compression pressure to attain optimal torque output.[22].The data in Figure 5 showed a comparison of torque output generated by an engine operating at a compression pressure of 11.8 Kg/cm2 and using three types of fuel, namely, RON 92, RON 95, and RON 100.From the engine speed range of 5000 RPM to 8000 RPM, it is evident that the engine using RON 100 gasoline produced higher torque output than the engine using RON 92 or RON 95 gasoline.Overall, the engine using RON 100 gasoline is capable of producing 5.3% more torque output compared to the engine using RON 95 gasoline [23].Utilizing on the data in Figure 5, engine torque output with compression pressure of 11.8 Kg/cm 2 using RON 95 and RON 100 gasoline is clearly depicted.For instance, in the engine speed range of 6000 RPM, the engine using RON 95 achieves a torque output of approximately 8.78 Nm, while the engine using RON 100 gasoline can produce 5.3% more torque, which is 9.25 Nm.Another example in the engine speed range of 8000 RPM, the engine using RON 95 only generates a torque result of 5.16 Nm, meanwhile the engine using RON 100 gasoline can achieve a 12% larger torque output, which is 5.79 Nm.
The engine using RON 100 gasoline is capable of producing more significant torque, with a variance of approximately 9.8%, when compared to the engine using RON 92 gasoline.Data from Figure 5 indicates that in the engine speed range of 5500 RPM, the engine using RON 92 gasoline only generates a torque result of 8.98 Nm, while the engine using RON 100 gasoline can generate higher torque, approximately 8.9% more, which is 9.78 Nm.This further underscores that employing large octane fuel in an engine with elevated compression pressure leads to optimal torque output.[24].

Power output comparison
Based on the data in Table 6, we can observe the comparison of power output from several compression pressure of engines fueled with RON 92 during the testing.Each power output value obtained through three times test, and the values listed in Table 6 are their averages.Generally, engine with higher compression pressure, which is 11.8 Kg/cm 2 , generated greater power output across all engine speeds [25].Table 6 records the generated power in Kilowatts (kW) for several compression pressure variations.The 10 Kg/cm 2 compression engine yielded lower power output compared to the 11.8 Kg/cm 2 compression engine.At compression pressure of 10 Kg/cm 2 , the peak power output only reaches 7.0 kW when the engine is running at 6000 RPM.On the other hand, the 11.8 Kg/cm 2 compression engine can achieve the same power outcome at lower engine speeds.This is because higher compression pressure results in better power output [26].Also from Table 6 provided a clear depiction of the power output patterns in engines with compression pressure variations fueled with RON 92 gasoline.In the 8000 RPM engine speed range, the engine at 11.8 Kg/cm 2 compression pressure produced 5.4 kW of power, whereas the engine at 10 Kg/cm 2 compression pressure yielded a power output that is roughly 28% less, amounting to about 4.2 kW at the identical engine speed.Besides the octane number of the fuel, compression pressure is also a factor that influences the value of power output [27].Based on the data in Table 7, the variations in power output among engines with different compression settings while using RON 95 fuel can be observed.. Overall, the 10 Kg/cm 2 compression engine also produced lower power output compared to the 11.8 Kg/cm2 compression engine.At compression pressure of 10 Kg/cm 2 , the highest power output only reaches 7.0 kW at 6500 RPM.Overall, the power output generated by engine using RON 95 gasoline inlined with 11.8 Kg/cm 2 compression engine is higher than the 10 Kg/cm 2 compression engine.Table 7 shown that the peak power output, which is 7.5 kW, recorded in the 11.8 Kg/cm2 compression engine when the engine is running at 6000 to 6500 RPM.On the other hand, at the same engine speed range, the 10 Kg/cm 2 compression engine only produced a power output of about 6.9 kW.This finding further reinforces the concept that engines with larger compression require higher-octane rating gasoline for optimal power output [28].
Jurnal Media Mesin, Vol. 25  The results of the power tests for several compression pressure variations when using RON 100 gasoline are recorded in Table 8.Overall, engine with high compression pressure, which is 11.8 Kg/cm 2 , also yielded larger power at all engine speeds.Conversely, engine with low compression pressure, specifically 10 Kg/cm 2 , tend to generated lower power across all engine speed ranges.The maximum power output generated by the engine with a compression pressure of 10 kg/cm 2 is only 7.0 kW.For instance, at 6500 RPM, the 10 Kg/cm2 compression engine produced power that is 8.6% lower than the 11.8 Kg/cm 2 compression engine.In the engine speed range of 7500 RPM, a power of 6.9 kW generated by the 11.8 Kg/cm 2 compression engine, which is 1.0 kW higher than the 10 Kg/cm 2 compression engine.More detailed data on engine power tests fueled with RON 100 gasoline can be observed in Figure 6.Comparison of power outcome evident across all engine speed.Using RON 100 gasoline with the 11.8 Kg/cm 2 compression engine also produced higher power outcome compared to the 10 Kg/cm 2 compression engine.This result clearly confirmed that engine with larger compression requires a higher-octane rating of gasoline to achieve optimal power output [29].
Based on data in Figure 7 clearly showed the power output comparison between the use of three types of fuel, namely RON 92, RON 95, and RON 100, in the 11.8 Kg/cm 2 compression engine in the engine speed range of 5000 RPM to 8000 RPM.It can be observed that the engine using RON 100 fuel produced higher power output than the engine using RON 95 or RON 92 gasoline [19].Overall, the engine fueled with RON 100 gasoline can produce power output that is 5.3% higher than the engine using RON 95 and 10% higher than the engine using RON 92 fuel.For instance, at 8000 RPM, the engine using RON 100 gasoline generates a power outcome of 6.46 kW, while the engine given RON 92 and RON 95 gasoline yielded lower power outcome with a difference of approximately 0.66 KW and 0.37 kW, respectively.The 11.8 Kg/cm 2 compression engine and using RON 100 gasoline achieved a peak power output of 7.9 kW when running at 6500 RPM.This test result reaffirmed that selecting the appropriate octane rating fuel for high compression engines will yield effective power output [28].

CONCLUSION
Internal combustion engine performnace is notably affected by both the compression pressure and the octane number of the fuel utilized.The test results indicate that when the 11.8 Kg/cm 2 compression engine uses RON 100 gasoline, it generates the highest torque and power output.
Therefore, selecting fuel with the right octane rating for the engine's compression pressure is crucial to achieving optimal power and torque output.While this testing provides insights into the relationship between compression pressure and fuel octane rating on engine performance, further research is needed to evaluate the impact of octane rating on carbon emissions produced by the engine.

Figure 2 .
Figure 2. Engine torque output at several compression pressure using RON 92 fuel

Figure 4 .
Figure 4. Engine torque output at several compression pressure using RON 100 fuel