The following equipment was used for the hydrogen production test using the ash solution:

1) Electrolytes: The electrolyte used is ash from the combustion of the pitted fruit of the oil palm or oil palm bunch (Figure 1).

Figure 1. Ashes from pitted oil palm fruit.

2) Hydrogen Generator: The hydrogen generator is shown in Figure 2.

Figure 2.Hydrogen generator.

3) Measuring devices: As shown in Table 1, they are used to measure various parameters during our work.

Table 1. Measuring and power supply devices.

Preparation of the electrolytic solution: To obtain the electrolytic solution, we dissolved 100 g of ash in 1 L of water and let the solution stand for 24 hours. During this time, we stirred it at least 10 times to ensure the potassium dissolved completely. After this time, we filtered the solution and let it stand for another 24 hours. A sediment formed at the bottom, leaving a clear solution above. Finally, from 100 g of ash in 1 L of water, we obtained 0.75 L of electrolytic solution.Figure 3below illustrates the different steps of the process in order.

Experiments and calculations carried out as part of our research: As part of the experiment, we have set up an experimental protocol for the production of hydrogen.

Experimental Protocol: The established experimental protocol is as follows:

1) Open the tank;

2) Add a precise volume of water to the tank;

3) Introduce a defined volume of the electrolyte solution into the reservoir;

4) Close the tank;

5) Open the bubbler;

6) Fill the bubbler halfway with water;

7) Close the bubbler;

8) Place a container equipped with a valve on the lid to prevent the return of the produced gas, at the end of the bubbler outlet pipe, for the collection of the produced gas;

9) Connect one terminal of the electrolyzer to the battery;

10) Start the vehicle;

11) Start the electrolyzer by connecting the second terminal to the battery;

12) Start the timer.

Figure 3. Preparation of the electrolyte solution before filtration.

After installing the required equipment, the following electrical diagram is obtained (Figure 4).

The gas produced is not pure hydrogen but a mixture of gases due to the absence of a separating membrane.

Figure 4.Electrical diagram of the system.

The experiment was carried out with a 12 V and 75 Ah battery while respecting 3 liters of the mixture (water + electrolyte solution) in the reservoir. The power source for the device is the current supplied by the battery. To prevent the battery from discharging during the experiment, we start the vehicle so that the alternator continuously charges the battery.

Other calculated parameters: Some parameters essential for analyzing the operation of production subsystems cannot be measured directly. To determine them, mathematical relationships must be used.

1) Actual power absorbed by electrolysis: This is the power used by the electrolyzer to perform the electrolysis of water; in our case, it corresponds to the power at the output of the voltage generator.

2) Useful power of electrolysis: This is the useful thermal power generated by the combustion or use of hydrogen (H₂) in the context of fluid engineering or energy, often applied to electrolyzer systems or heat engines [11].

P u : Useful power, expressed in watts (W) or kilowatts (kW), representing the thermal energy delivered.

PCI : The lower heating value of hydrogen, typically 120 to 286 kJ/mol or 10 to 13 kWh/kg depending on the units, measures the energy released per unit mass without condensation of water vapor.

Q v H 2 : Volumetric flow rate of hydrogen (in m³/s or m³/h), indicating the quantity of H₂ gas consumed per unit of time.

ρ: Reference density of hydrogen under normal conditions (in kg/m³, often 0.0899 kg/m³ at 0˚C and 1 atm).

3) Electrical energy consumed: The electrical energy consumed is obtained by multiplying the power at the output of the voltage generator by time.

4) Useful yield: This is the ratio of useful power to the power of the voltage generator.

5) Electrolyzer efficiency: The operating efficiency of the electrolyzer can be calculated using the formula below [12].

V ˙ HHO , t is the theoretical volumetric flow rate and V ˙ HHO , r the real volumetric flow rate.

The total volume of HHO gas produced by the cells of an electrolyzeris given by the following equation [11].

V HHO , t : defines the total volume of an HHO gas (oxygen and hydrogen mixture produced by electrolysis of water);

V H 2 : volumes of dihydrogen;

V O 2 : volumes of dioxygen.

According to Faraday’s law, in the case of water electrolysis at a constant current, we have the following formula which defines the moles number (n) of substance produced or consumed during an electrochemical reaction.

with n: Quantity of substance released (mol).

I: Current intensity (A).

t: Time during which the current is applied (s).

F: Faraday constant (A · s · mol⁻¹), F = 96485 A · s · mol⁻¹.

Z: Number of moles of electrons exchanged (ZH₂ = 2 and ZO₂ = 4).

Under standard temperature and pressure (STP), hydrogen is considered an ideal gas. Therefore, we have:

with P: Gas pressure (atm).

V: Volume of the gas (L).

R: Ideal gas constant (L · atm · mol⁻¹ · K⁻¹), R = 0,08205746 L · atm · mol⁻¹ · K⁻¹.

T: Temperature (K).

By combining equations (6)-(8), we obtain the theoretical volume of the gas produced, which is:

By taking the chosen current value for the operation of electrolyzer, the theoretical volumetric flow rate is given by the formula [11] below:

In this experiment, we varied the concentration of the electrolyte in order to record the parameters of hydrogen production, namely: voltage and current. The unit Ls/Le stands for “liters of core solution per liter of water.” For example, 0.5 Ls/Le means 0.5 liters of core solution per liter of water. The total volume of the electrolyte solution is 1.5 liters in this case.

Figure 5.Evolution of voltage as a function of the concentration of the electrolytic solution.

Figure 5 illustrates the voltage evolution as a function of the concentration of the mixture (water with electrolyte solution). A progressive decrease in voltage is observed with increasing concentration. The voltage drops from approximately 13.41 V to 11.07 V when the concentration varies from 0.2 to 2 Ls/Le. This trend can be explained by the improvement in the conductivity of the electrolyte solution as the concentration increases, which reduces the internal resistance of the system. Thus, for each given concentration, the voltage remains stable. For a battery being charged in a vehicle with the engine running, the voltage varies between 13 and 14 V. Therefore, the voltages obtained for concentrations of 0.2 and 0.5 during the tests are reliable.

Figure 6. Evolution of intensity as a function of the concentration of the electrolytic solution.

Figure 6 shows the evolution of current intensity as a function of the mixture concentration. An increase in current intensity is observed as the concentration increases. The current intensity varies from 26 to 90 A for concentrations ranging from 0.2 to 2 Ls/Le. This suggests that increasing the concentration improves the conductivity of the solution, thus facilitating the flow of electric current. This behavior could be attributed to a greater availability of ions in the solution, increasing the efficiency of the electrochemical process. High current intensity in the electrical circuit of a motor vehicle causes the connecting wires to heat up. Therefore, the current intensities of 26 A and 36.6 A obtained in our experiments are favorable.

The temperature evolution during the production time is shown in Figures 7-11 according to the concentrations used. The temperature during production increases with the production time for the different concentrations.

Figure 7. Temperature evolution over time for 0.2 Ls/Le.

Figure 7 illustrates the temperature evolution over time for a concentration of 0.2 Ls/Le. A gradual, linear increase in temperature is observed as time passes. The temperature varies from 30˚C to 35˚C during the production time of 4 minutes and 10 seconds. For a concentration of 0.5 Ls/Le (Figure 8), the temperature varies from 30˚C to 34˚C during the production time of 1 minute and 31 seconds. Similarly, the graph reveals a more moderate temperature increase compared to the case of concentration 0.2 Ls/Le.

Figure 8. Temperature evolution over time for 0.5 Ls/Le.

Figure 9.Temperature evolution over time for 1 Ls/Le.

Figure 9 illustrates the temperature evolution over time for a concentration of 1 Ls/Le. The temperature varies from 30˚C to 36˚C during the production time of 1 minute and 35 seconds. The graph also shows a relatively rapid temperature rise, suggesting a higher intensity, probably due to the increased concentration of the solution, which promotes electrical exchange and exothermic chemical reactions. This result highlights the importance of monitoring the temperature to avoid any risk of overheating.

Evolution of temperature for concentration 2 Ls/Le is shown on Figure 10.

Figure 10.Temperature evolution over time for 2 Ls/Le.

This graph shows a gradual and almost linear increase in temperature over time, rising from 30˚C to 37˚C between 0 and 75 seconds. The relatively rapid temperature rise suggests a higher intensity, likely due to an increased volume of solution facilitating electrical exchange and exothermic chemical reactions. This result also highlights the importance of monitoring the temperature to prevent any risk of overheating.

Analysis of Figures 5-10 shows that the electrolysis parameters, particularly voltage, current, and temperature, vary depending on the concentration of the electrolytic solution. A higher concentration improves the conductivity of the mixture (electrolytic solution + water), reducing the required voltage (Figure 5) while increasing the current for better gas production (Figure 6). Figures 7-10 show that the 0.5 Ls/Le concentration exhibits a smaller temperature variation than other concentrations. To ensure stable electrolysis parameters, choosing 0.5 Ls/Le appears to be a good compromise, as it allows for a moderate and better-controlled temperature increase while offering a reasonable filling time (1 minute 31 seconds). This volume thus guarantees stable and efficient electrolyzer performance.

The actual gas flow rate produced by the electrolyzer increases rapidly up to the optimal concentration point of 0.5. After 0.5, the growth is slow with increasing concentration. From 0.2 to 0.5 L/min, production increases rapidly from 0.058 to 0.494 L/min. From 0.5 to 2 L/min, this production increases from 0.494 to 0.56 L/min.

Figure 11. Flow rate variation as a function of concentration.

Figure 12.Production volume as a function of concentration.

The production volume curve in Figure 12 shows three zones: a zone of rapid increase between concentrations of 0.2 Ls/Le and 0.5 Ls/Le, a zone of slow growth increase 0.5 Ls/Le and 1 Ls/Le, and a zone of decrease from 1 Ls/Le to 2 Ls/Le. The point at coordinates (0.5 Ls/Le, 0.75 Ls/Le) constitutes an inflection point for the production volume curve.

We can also note from Figure 13 that the production time of hydrogen for the concentration of 0.2 Ls/Le is high while those of the concentrations of 0.5 Ls/Le, 1 Ls/Le and 2 Ls/Le are relatively low.

In terms of hydrogen production, a concentration of 0.5 Ls/Le represents optimal production.

Figure 13. Evolution of production time as a function of concentration.

In order to determine parameters not directly measurable, the voltage and current are those obtained at a concentration of 0.5 Ls/Le. The theoretical volume is determined assuming that the electrolyzer operates under standard temperature and pressure (STP) conditions, with a current of 1 A for 1 minute [11].

To determine the energy efficiency of the electrolyzer, 10 tests were carried out for a concentration of 0.5 Ls/Le, the production times of which are recorded in Table 2 below.

Table 2. Table type styles.

The average time obtained is 91 seconds. The production for this average time is 0.75 L.

Using these different data points, we have the calculated parameters which are grouped in Table 3 below:

Table 3. Table type styles.

For this concentration, the efficiency of the electrolyzer is 43% with the use of the ash solution. This efficiency confirms that ashes can indeed be used to produce hydrogen for the operation of internal combustion engines and for industrial use.