The Effect of Heating of B20 Fuel to Combustion Characteristic on the Diesel Engine Based on Experiment

– a ccording to Bank Indonesia, the current account deficit of Indonesia. In the second quarter of 2018 increased to USD 8.0 billion. One of the government's programs to reduce the current account deficit is by implementing a B20 biodiesel policy. The increasing percentage of biodiesel in fuel blends tends to decrease the quality of spray atomization, where it indicated by longer droplet breakup, spray penetration, droplet lifetime, and bigger droplet diameter. Higher viscosity causes a decrease in the quality of the spray from the injector. Previous research shows that the inlet temperature of the fuel can make the performance of small diesel engines slightly better. The research was conducted using petrodiesel and biodiesel fuel by varying inlet temperature of 50 o C and 70 o C. Based on that this research is conducted to understand the effect of fuel heating diesel engine combustion process. The result shows that generally maximum pressure is increased for every increase in fuel temperature. The heat release shows a decreasing trend for every increase in fuel temperature. Knock detection shows that generally when the fuel temperature increased the knocking is also increased. The increasing fuel temperature shows little effect on ignition delay except for the higher temperature of 60 o C and 70 o C where the ignition delay is the lowest and closest to that of a dexlite fuel.

engines from transportation to production. Starting from September 1 st 2018, by ministerial decree 1936 K / 10 / MEM / 2018 about the procurement of biodiesel fuel from September, Indonesia started to effectively be commercialized the B20 fuel through several companies as producer and suppliers. This is done to reduce diesel fuel import budget for Indonesia.
Biodiesel fuel has advantages compared to diesel fuel. According to [3] these advantages are made from renewable sources, better emissions, and better lubricating property. The disadvantage of Biodiesel is more expensive than fossil fuel, less suitable for low temperatures, and has a higher viscosity than pure diesel fuel.
Biodiesel is chemically referred to as methyl ester or ethyl ester of fatty acids produced from plant vegetable oils or animal oils. Biodiesel derived from vegetable oil is made by converting triglycerides into fatty acids, using the catalyst in the esterification process. Biodiesel has the same physical and chemical properties as conventional diesel fuel. In general, biodiesel has an energy content that is almost close to diesel fuel. So it can be used to power engines for transportation and for agricultural purposes.
There are several factors like ignition delay, knocking, Rate of heat release, and pressure affecting the combustion process of the combustion chamber. Each of these factors is caused by different variables whether it's the fuel calorific value, fuel cetane number, fuel spray pattern, injection timing etc. All of those factors can affect the performance of the engine.

A. Ignition Delay
Theoretically the combustion process in a diesel engine starts when the piston compresses the air in the combustion chamber, then when the piston reaches the International Journal of Marine Engineering Innovation and Research, Vol. 5(1), Mar. 2020. 1-9 (pISSN: 2541-5972, eISSN: 2548-1479 2 Top Dead center, the fuel is injected which will burn by itself because the temperature of the combustion chamber has reached the flashpoint of the fuel. In fact there is a delay since the start of fuel injection with the occurrence of combustion. This delay is called Ignition delay [4]. The main reason for ignition delay depends on the cetane number (CN) of the fuel used. Cetane number is a number that provides a measure of ignition characteristics of diesel fuel when it is burnt in the diesel engines. The fuel which has a lower cetane number has longer ignition delay characteristics [5].

B. Maximum Pressure
One of the factors of the combustion process is the pressure produced by the combustion. In the diesel engines, the peak pressure of the combustion chamber depends on the fraction of fuel burned during the premixed burning phase, i.e initial stage of combustion. The pressure of the cylinder characterizes the ability of the fuel to mix well in the air and burn [6].

C. Rate of Heat Release
The rate of heat release is defined as the heat released from a chemical in a given time. By knowing the heat release rate parameter, some of the combustion phenomena in the engine cylinder can be analyzed. Phenomena parameters such as combustion duration and intensity can be easily estimated from the heat release rate diagram [7]. The heat release rate and the diagram is shown in figure 1 and figure 2.

D. Knocking
Sometimes Diesel engines can experience abrupt cylinder pressure rise due to the rapid increase of fuel combustion rate. This is sometimes because of the fuel has longer ignition delay, the burning of the first droplets is longer, and more fuel is accumulated in the combustion chamber. Then when the ignition occurs, it burns violently and creates pressure oscillations. This phenomenon is called knocking [8].
There are several ways to improve engine performance. It is proven that by increasing the injection pressure there is an increase in engine power because of better combustion [9]. The second way to improve this is to add the number of nozzle holes for better spray distribution and improving the hole geometry of the nozzle. This way it is computationally proved that more nozzle hole and improved hole geometry have a better effect on the performance of a diesel engine [10]. This concept is also proven to be good on CNG marine Engines [11].
According to research conducted by [12]. In the research the fuel used was diesel fuel (B0) and up to Biodiesel (B100). In the research the combustion characteristic of both fuels was also analyzed. The result, was quite significant, by using Biodiesel (B100) the ignition delay is increased by 4 degrees and the total heat release is decreased until 26% compared to pure diesel fuel.  [12] International Journal of Marine Engineering Innovation and Research, Vol. 5(1), Mar. 2020. 1-9 (pISSN: 2541-5972, eISSN: 2548-1479 3 Research conducted by [13] proves that the inlet temperature of the fuel can make the performance of small diesel engine slightly better. The research was conducted using petrodiesel and biodiesel fuel by varying inlet temperature of 50 o C and 70 o C and observing the effect on engine brake thermal efficiency and brake specific fuel consumption.
The research shows that the effect of fuel temperature on brake thermal efficiency of the biodiesel at inlet temperature of ambient temperature, 50 o C and 70 o C. It is shown that there is an increase of brake thermal efficiency as shown in the figure 3. Figure. 3. Brake Thermal Efficiency vs load Graph [13].
The increase of Brake Thermal Efficiency is due to the weakening fuel chain hence better combustion can be achieved. With better combustion, it is expected that the performance of the engine is increased. On Brake Specific Fuel Consumption (BSFC), there is a slight reduction of BSFC in both petrodiesel and Biodiesel at inlet temperature 70 o C as shown in the figure 4. Based on the research conducted by [12,13] a further research needs to be conducted to seek the best inlet fuel temperature based on performance, spray characteristic and combustion characteristics. The research is also to be made with bigger diesel engine compared to the research done by [13] in order to see how much the effect of fuel preheating will take place. The effect of preheating can also be seen by doing combustion characteristic test on preheated fuel.

III. RESULT AND DISCUSSIONS
The engine ran at 1800 RPM and 2000 RPM with 100% load. The fuel heating is done by using a heat exchanger installed as a bypass on the engine cooling system. Fuel temperature is controlled by a solenoid valve which is controlled by a thermostat. The valve is located on the water intake of the heat exchanger.
The engine will be attached to a rotating encoder and pressure transducer which will be connected to combustion analyzer. The data from combustion analyzer is taken from the prechamber/swirl-chamber of the engine. Analysis of combustion process is using TMRInstrument sensor and SYSMONSoft as data acquisition. Setup experiment can be seen in figure 5   The fuel used in this experiment is B20 named "bio solar" which has widely used in Indonesia and as for comparison, B0 fuel is used named "dexlite". The specification for B20 is shown in table 1. The Engine that is used in the research is Mitsubishi 4D30. The engine specification is mentioned in table 2.  Figure 7 showing the maximum Pressure graph analysis at 1800 RPM for B20 fuel with fuel variation and dexlite as comparison. It can be observed that B20 fuel at      Figure 11 is the knock Detection graph analysis at 1800 RPM. The graph shown the knock detection for B20 inlet temperature ranging from 30 o C to 70 o C and Dexlite for comparison. B20 fuel at 30 o C has highest point of knocking at 0.82 at 7 o after TDC. B20 fuel at 40 o C has highest point of knocking at 0.96 at 14 o after TDC.    Figure 13 is showing the ignition delay of B20 fuel for every inlet temperature. The ignition delay for B20 at 30 o C inlet temperature is 1.111 ms. Ignition delay for B20 at 40 o C inlet temperature is 1.111 ms. Ignition delay for B20 at 50 o C inlet temperature is 1.018 ms. Ignition delay for B20 at 60 o C inlet temperature is 1.018 ms. Ignition delay for B20 at 70 o C inlet temperature is 1.018 ms. While Dexlite achieve the lowest ignition delay at 0.925 ms. Ignition delay time depends on the value of cetane number of the fuel. The higher the cetane number of a fuel, the faster the time takes for the fuel to ignite. There fore higher cetane number means shorter ignition .

D. Ignition Delay
delay. In this case Dexlite has shorter ignition delay. This is due to the fact that Dexlite has cetane number of 51. While B20 (Biosolar) has cetane number of 48. Figure. 14. Ignition Delay Graph. Figure 14 is showing the ignition delay of B20 fuel for every inlet temperature. The ignition delay for B20 at 30 o C inlet temperature is 0.916 ms. Ignition delay for B20 at 40 o C inlet temperature is 1 ms. Ignition delay for B20 at 50 o C inlet temperature is 1.083 ms. Ignition delay for B20 at 60 o C inlet temperature is 0.916 ms. Ignition delay for B20 at 70 o C inlet temperature is 0.833 ms. While Dexlite achieve the lowest ignition delay at 0.833 ms.
Ignition delay time depends on the value of cetane number of the fuel. the higher the cetane number of a fuel, the faster the time takes for the fuel to ignite. There fore higher cetane number means shorter ignition delay. In this case Dexlite has shorter ignition delay. This is due to the fact that Dexlite has cetane number of 51. While B20 (Biosolar) has cetane number of 48.
IV. CONCLUSIONS B20 Temperature can affect the combustion characteristics with detail as follows: • Based on Maximum pressure graph, it is shown that there is an increasing trend of pressure when the fuel inlet temperature is increased. But the trend goes downward on high temperatures like 60 o C and 70 o C. The result also shows that there is little effect on the crank angle of highest pressure is achieved. The highest pressure is always achieved at 7 to 8 degrees after TDC. • Based on Heat Release rate graph, it is shown that there is decreasing trend on the peak value of heat release rate for when the fuel inlet temperature is increased. This is due to the fact that increasing temperature of fuel inlet causing the fuel density to goes down while the plunger of the injection system has the same volume, so the fuel mass per injection goes into the combustion chamber goes down. The result also shows that mostly the crank angle of highest heat release rate is longest when the fuel inlet temperature is 50 o C for every RPM.
• Based on Knock Detection Graph, it is shown that the knocking is generally higher when the temperature of the fuel inlet is increased. The crank angle of the highest point of knocking is varied between first peak at 7 o -8 o Before TDC or 14 o -15 o C after TDC. • Based on Ignition delay graph, it is shown that the temperature increaseonly give a slight effect on ignition delay. The closest temperature and condition to approach the value of dexlite is at higher temperatures of 60 o C to 70 o C.