Design of Output Power Control System Based on Mass Flow Rate Comparison of Air-Fuel Ratio (AFR) on Dual Fuel Generator Set by Using PID Control Method

Currently, biogas as an alternative fuel has been widely used in the community, including in lamps and biogas stoves. There has been a surplus of biogas in some production regions due to a relatively small need for biogas fuel. So that most biogas users utilize the surplus to become generator fuel. Yet, in the application there is a drawback, namely the instability of the electric power generated per unit time. This is caused by not achieving the optimal water-fuel ratio because the volume of biogas production from the reactor is fluctuating based on the volume of raw material, such as processed cow dung. Therefore, a control method using a PID Controller is constructed to determine the best value of the AFR on a dual fuel generator. The objective is to generate an optimal output of electric power. The generator set is a tool used to generate energy or electrical power. The electric power generated by the generator set used to supply the electrical loads in this research are lamps. Power produced by a generator set ranges from 100 to 1200 watts. The power generated by the generator set is affected by a mixture of air and fuel. The generator set is dual fuel. From the results of this study, a stable response with an overshoot value is below 0% and its error is 2%. In addition, the best-obtained value of the AFR is 15.06. Furthermore, the stability of the power generated by the generator set is also influenced by the flow rate mass of the fuel injected into the combustion chamber. From the simulation results, when given a power set point at 1200 watts, the obtained value of the air mass flow rate is 0.03754 kg/s, the mass flow rate of biogas is 0.002367 kg/s, and the gasoline constant mass flow rate is 0.000125 kg/s. Meanwhile, when given a set point of 100 watts and a value of 0.009928 kg/s air mass flow rate is injected into the chamber, the mass flow rate of biogas is 0.0005341 kg/s, and the mass flow rate of gasoline is 0.000125 kg/s. In this research, the value of AFR for complete combustion on a dual fuel system is 15.06. The results have shown that the PID Controller has been successfully implemented to regulate AFR, and the generator output of power can be constant.

Air ruel ratio; Biogas; Generator; PID control system

This means renewable energy development is growing. Indonesia, especially, has huge potential for it. Fossil fuels fulfill a major part of the world's energy demand. Higher demand for energy, depletion of fossil fuels, and environmental impacts are the key motivational factors for exploring alternative energy sources (Khatri and Khatri, 2020). Based on the geographic state, Indonesia is abundant with a high amount of energy resources, ranging from hydro, geothermal, biomass, solar, wind, and oceanic sources. Unfortunately, such property has not been widely used as energy sources that could replace the fossil fuel-based energy sources that are nearly depleted. Renewable energy resources are increasingly being used to cover the electricty grid demands in many countries. A current theoretical question that is interesting in terms of introducing a long-term perspective, pertains to what an energy supply from exclusively renewable energy resources could look like. Amounts of fuel from bioenergy are assumed to be annually available. This amount is derived from a study on bioenergy from agricultural waste conducted by GIZ (Günther, 2018). The development of biogas in Indonesia is still relatively slow due to various factors, ranging from people who are still not comfortable with dirt as an energy source to biogas purification problems and the implementation of the generator set (Abdurrakhman & Soehartanto, 2014). Nowadays, in many industrialized countries, the conversion of municipal organic or solid waste to biogas has become popular in recent years as a sustainable technology that can produce green energy and electricity (Tetteh et al., 2018). In Indonesia, biomass generally has the potential to be used for long-term balancing of society’s demand. The biomass itself can be stored for a certain amount of time and place, and the secondary energy carrier (e.g., biogas) can be stored for a very long time (Günther, 2018). Currently, the Indonesian government has been anticipating the development of Distributed Renewable Energy Generation (DREG) using environmentally friendly energy sources for local electrical energy supplies and has developed local sources of renewable energy (Nazir et al., 2016).

Based on data from the Directorate General of Livestock and Animal Health, the number of beef cattle in 2015 reached 15 million. One cow is able to produce manure 23.6 kg of solid waste a day and 9.1 kg or liquid waste a day (Setiawan, 2002). One kg of cow or buffalo manure can produce 0.023 to 0.040 m³ of biogas (Stewart et al., 2007). The process of biogas production depends many factors in environment (Abdurrakhman et al., 2018). Therefore, the maximum potential value of biogas produced by manure is as high as 14.16 million m³/day. The methane amount is 9,912 million m³/day and CO² is 4,248 million m³/day. In other words, within a year, Indonesia will contribute 1.55 billion m³ CO₂ or the equivalent of 2.77 million tons per year. Indonesia will also contribute the amount of 3.617 billion m³ methane, equivalent to 6,466 million tons per year. The effect of methane gas is equivalent to 21 times the CO₂ of greenhouse gases. The contribution of methane gas will be equivalent to 135.8 million tons of CO₂ per year. It means that by the addition of these gasses in the atmosphere, methane gas is equivalent to 135.8 million tons worth of CO₂ gasses a year. Levels of H₂S contained in the biogas can be harmful to users because at levels of more than 500 ppm, biogas can cause lung damage and even lead to death (Noyola et al., 2006).

Currently, several biogas purification methods have been developed. The methods are absorption, adsorption, cryogenic, membrane, and carbon mineralization technology (O’Brien, 1991). Literally, the gas-liquid absorption method with a water scrubber system is a priority among biogas purification applications because its main ingredient is water, which can be relatively cheap, available, and environmentally friendly (Budzianowski et al., 2017). If water temperature is between 10-20°C, CO₂ gas solubility level is between 2.5 to 1.6 g per kg of liquid gas. Meanwhile, within the same temperature range, it will be able to dissolve the H₂S gas at 5.5 to 3.9 g per kg of liquid gas (Medard, 1976).

A dual fuel generator set is a standard gasoline engine with biogas fuel added in its combustion chamber. The engine’s ignition is powered by a gas spray called pilot fuel. In other words, liquid or gaseous fuels can be injected into the engine by making a hole in the intake manifold of the engine itself. When the type of added fuel typs is liquid, such as ethanol or methanol, carburetor is added to the system. This makes the fuel pump at a certain pressure and become atomized as the fuel is injected into the air intake. As for the fuel gas, it is not needed anymore since the gas fuel carburetor already has its own pressure (Setiawan, 2002). Hotta et al. (2019) explored the potential of raw biogas as an alternative and standalone fuel for gasoline-fueled spark ignition (SI) engines. A single cylinder spark ignition engine is operated with both gasoline and raw biogas at a compression ratio of 10 under wide open and part-throttle conditions. The baseline test is performed with gasoline, and subsequent experiments are carried out with raw biogas. The engine performance, combustion, and emission parameters are measured over a range of speed variations (1450–1700?rpm). A comparative analysis of the result showed 18% of reduction in brake power, 66% increase in brake specific fuel consumption, and 12% reduction in brake thermal efficiency when the engine is fueled with raw biogas. Ambarita et al. (2017) concluded that the output power and specific fuel consumption of the Compression Ignition (CI) engine ran in dual-fuel mode are higher than the CI engine ran in pure diesel mode. The brake thermal efficiency of the CI engine ran in dual-fuel mode was strongly affected by the biogas flow rate and methane concentration. An optimum biogas flow rate for a maximum brake thermal efficiency exists. The biogas can reduce the diesel fuel consumption significantly.

A dual fuel system’s advantages include conserving the use of gasoline as fuel, production costs that can be minimized, and generator set modification costs are relatively cheaper than converting to a whole gas engine. Furthermore, the application of biogas with a dual fuel system on the generator set can improve the performance and efficiency of the engine (Bastida et al., 2017). The utilization of a biogas generator set will not change the composition of machine tools and only add to the system equipment, such as a mixer venturi on the suction channel. The use of dual fuel intended to reduce the use of gasoline in the combustion process would entail a partial substitution of gasoline by biogas. Verma et al. (2019) performed an experimental investigation on a diesel-biogas dual fuel (DF) engine based on energy and exergy analyses. The analyses included the effects of change in the compression ratio (CR), exhaust gas recirculation (EGR), and EGR temperature on the performance and emission characteristics of a DF engine. The results showed that the highest efficiencies at both low and high loads were obtained with hot EGR cases. At the same time, exhaust emissions could also be kept in check. Mixing biogas as engine fuel was studied by Verma et al. (2017) to determine the effect of variations in the composition of biogas on the performance of diesel engines for dual fuels using exergy analysis. The variation of biogas composition was 93% (BG93), 84% (BG84), and 75% (BG75). The AFR produced is 22.47 for BG 93, 16.77 for BG84, and 13.49 for BG75. In another study, de Faria et al. (2017) conducted a thermodynamic model to predict the performance of a spark ignition engine using biogas fuel. Moreover, it was concluded that the increased load results in a higher engine airflow that increases power output at a constant engine speed, which is greater than fuel consumption, resulting in a smaller overall specific fuel consumption (sfc). In addition, the simulation states that spark timing has opposite effects at NOx and sfc levels.

A generator set using a dual fuel system still needs a lot of work in the development phase. One of the items is the generator set’s output power controls. The generator set’s output power control needs to be designed so that the generator set is able to produce a maximum and stable output of power in accordance with daily electricity needs. In order to make the generator produce a stable output of power for demand, the mass flow rate of fuel and air in the combustion chamber of the engine should be consistent with the required power demand. If more power from the generator’s output is required, then the mass flow rate of air and fuel (petrol and biogas) entering the combustion chamber will also be getting bigger. Additionally, the mixture of fuel and air must be in accordance with combustion reaction rules. Therefore, to obtain optimum combustion, the calculation of the AFR is performed by stoichiometric equation.

The main objective of this study is the determination of flow rate values ??from air, biogas, and gasoline based on the standard AFR value. The results of this study are expected to be utilized by biogas users who will use it as a mixed fuel in the engine to produce electricity. This needs to be analyzed so that the use of biogas can be optimal, especially in certain production areas that leverage livestock manure. In some of these areas, biogas production is usually only used for biogas lamps and stoves, while the rest of the production is not utilized properly, even though electricity demand is relatively high.

The desired design in this system is the value of a stable output of power in accordance with a given load. In this system, there is a non-linear function that is connected between pressure input and output on the throttle valve. For a non-linear system, there are many methods used to control disturbance, feedback stabilization, and performance enhancements, such as research by Humaidi et al. (2019) that uses an extended state observer (ESO). It produced smaller peaking and had immunity against measurement noise and parameter variations. A non-linear controller has also been used to control the angle of the roll channel for delta wing aircraft with the presence of wing rock phenomenon using the Lyapunov method and the zero-convergence with a MATLAB simulation (Humaidi et al., 2019). In some more complex plants, an active disturbance rejection control (IADRC) is needed to overcome disturbances and uncertainties and outperform systems (Najm and Ibraheem, 2020).

Non-linear systems can also use non-linear PID (NPID). The NPID control has been found in two categories of applications: (1) Non-linear systems, where NPID control is used to accommodate the non-linearity, usually to achieve consistent responses across a range of conditions for the system; (2) Linear systems, where NPID control is used to achieve performance not achievable by a linear PID control system, such as increased damping, reduced rise time for step or rapid inputs, and improved tracking accuracy (Su et al., 2005). Non-linear PID controllers are divided into two categories: first, the controller gain is directly related to the magnitude of the state. Second, it uses phases, such as a parameter to modify this controller gain (Abdul-Adheem et al., 2017). In this paper, the PID controller is used to maintain the stability of the power generated by the generator set, and the performance of the control system is analyzed.

Based on the results of this research, a stable output power response occurs with an overshoot maximum value that average below 20% and an error value below 2% in each of the set point values between 100-1200 watts. In addition, the PID parameter values are Kp = 120, Ki = 0.1, and Kd = 15.2. The PID parameter values ??for the flow rate control of biogas are Kp = 5, Ki = 3, and Kd = 1. In addition, there is a difference between the simulated and real scenario mass flow rates, with the average biogas mass flow rate of 6.94% and the mass air flow rate at 7.36%. The amount of power generated by generator set and the mass flow rate of air and fuel will increase. For the maximum power of 1200 watts, the obtained air mass flow rate amounted to 2.118 kg/s, the mass flow rate of biogas amounted to 0.133 kg/s, and the gasoline mass flow rate amounted to 0.01 kg/s. For the minimum power, the obtained air mass flow rate amounted to 0.560 kg/s, the mass flow rate of biogas amounted to 0.029 kg/s, and the gas mass flow rate amounted to 0.01 kg/s. In this research, the value of the AFR for complete combustion on a dual fuel system is 15.06. The results have shown that the PID Controller can be successfully implemented to regulate AFR, and the generator’s output power can be constant.

This study was made possible with the help of KPSP Setia Kawan Nongkojajar, Pasuruan, Testing and Calibration Laboratory, Industrial Instrumentation Laboratory, and the Department of Instrumentation Engineering ITS as data providers. The authors would like to thank the Directorate of Research and Community Service Institut Teknologi Sepuluh Nopember through Contract No. 1386/PKS/ITS/2018 for funding this research in 2018.

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