Sustainable Production of Green Oxy-Hydrogen from Vehicles’ Air Conditioning Drains to Enhance Engine Efficiency and Reduce Greenhouse Gas Emissions

Abstract

Innovative and sustainable solutions are increasingly necessary as concerns about fossil fuels’ environmental and economic impacts grow. Accordingly, this study aims to enhance vehicle internal combustion engine efficiency by producing oxy-hydrogen (HHO) from drain water from the vehicle air conditioning system and utilizing it as a secondary fuel. A 1600 cc Daewoo engine equipped with electronic fuel injection was employed as the test subject. Initially, the engine’s performance was evaluated using various gasoline variants, 80, 92, and 95. The 92-octane gasoline demonstrated the highest efficiency, achieving a peak power of 113 kW and torque of 190 Nm. The engine had an 11:1 compression ratio. Then, different flow rates of oxy-hydrogen, 50, 248, 397, and 480 mL/min, generated from the air conditioner drain were combined with 92 fuel. A significant improvement was observed with the increase in the flow rate of oxy-hydrogen gas to the 92 fuel. The results indicated that incorporating 480 mL/min oxy-hydrogen gas into the fuel led to an 8.7% reduction in fuel consumption, 5.5% enhancement in thermal efficiency, and 7.9% in volumetric efficiency. Greenhouse gas emissions reductions of carbon monoxide, carbon dioxide, and hydrocarbons were recorded as 18%, 9.2%, and 9%, respectively. At the same time, nitrogen oxides increased by 12.5%. Therefore, utilizing a vehicle air conditioner drain water to generate oxy-hydrogen gas fuel in conjunction with 92-octane gasoline is an efficient solution to reduce fuel consumption, enhance energy efficiency, and mitigate the adverse effects of pollution. This approach also contributes to progress towards a more sustainable future.

1. Introduction

Climate change-induced global warming has increased the adoption of air conditioning systems [1,2,3]. Many studies are being conducted to replace fossil fuels in vehicles, such as through the production of electric vehicles or by reducing their use with the addition of HHO gas [4]. Pure water is commonly used to generate hydrogen through electrolysis, in which electrical energy dissociates water into hydrogen and oxygen gases. Despite the effectiveness of producing HHO gas from pure water, the increased cost of its production, in addition to the large consumption of water resources, has necessarily necessitated the search for suitable alternatives [5,6]. The drain water from air conditioning is naturally distilled and considered exhaust water; therefore, its reuse in HHO production is a prominent idea. Despite the effective role played by air conditioners in improving living and working conditions, the overload on the engine resulting from their operation contributes to the emission of greenhouse gases such as carbon dioxide (CO₂) and hydrocarbon (HC) gasses. Air conditioners consume 20 times more electricity than ceiling fans, accounting for 10–20% of the world’s energy use [7,8,9]. An air conditioner uses a refrigeration cycle to replace heated air with more relaxed, humid air in a confined space. AC is widely used in homes, offices, and cars in hot and humid conditions to reduce interior air temperature and improve comfort [10,11]. Since drain comes from atmospheric moisture, it has a high-quality chemical makeup and requires little or no treatment before being stored or utilized for direct irrigation [12,13]. Air conditioning units create different amounts of drain depending on humidity. Depending on capacity, modern air conditioners produce 15–70 L of water daily. For instance, a 2000-pound air conditioner running for 7–8 h may generate about 10 L of water. Without proper collection, this drain is usually discharged into sewage systems or evaporated [14]. Although often overlooked, drain water can be reused for non-potable purposes such as industrial use, irrigation, and toilet flushing [15,16,17]. HHO generators can reuse this drain water. Large-scale hydrogen generation is most economically viable with alkaline water electrolysis (AWE) [3]. AWE uses hydroxy (OH⁻) ions as the principal ionic species, operating at 20–80 °C, 1.8–2.4 V, and 0.2–0.4 A/cm² [18,19]. AWE cells use aqueous KOH or NaOH, while proton exchange membrane (PEM) electrolyzers use H⁺ ions and PFSA membranes [19]. At temperatures above 700 °C, solid oxide electrolysis cells (SOECs) use oxide ions (O₂⁻). SOECs use yttrium-stabilized zirconia as the solid electrolyte [19]. NaOH and KOH are the most frequent AWE electrolytes due to their high hydrogen ion concentrations (pH 13–14) [3]. AWE requires a constant power source and has a lengthy start-up time, but it is one of the more accessible hydrogen generation processes [20]. Electrolysis is performed in wet-type electrolyzers with electrodes immersed in electrolyte. When a direct current is passed through an electrolyte solution, an oxidation-reduction reaction occurs at the electrode surfaces. This reaction releases electrons at the anode, oxidizing water to form oxygen gas. To prevent the mixing of the produced gases, the electrodes must be separated by a porous barrier that allows the passage of ions, but prevents the passage of gases [21]. Factors influencing HHO gas production efficiency include electrode surface area, electrolyte concentration, and temperature, while operating pressure and power source type have an indirect impact. HHO gas generation depends on the electrode and electrolyte, with SS grade 316L being the most popular and KOH and NaOH being the most common [22]. Gas generated by electrolysis is usually stoichiometric. Equations (1) and (2) show cathode and anode reactions [11]. Equation (3) shows water splitting into hydrogen and oxygen.

At the cathode: 2H₂O + 2e⁻ → H₂ + 2OH⁻

(1)

At the anode: 4OH⁻ → O₂ + 2H₂O + 4e⁻

(2)

The overall reaction is represented as: 2H₂O → 2H₂ + O₂

(3)

The gas produced via water electrolysis, commonly called HHO, was historically known as oxy-hydrogen or Brown’s gas owing to its unique chemical makeup [23]. Electrolytes are crucial, with alkaline solutions favored over acidic ones because of their higher reactivity and corrosion resistance [24]. The automotive industry, a major consumer of fossil fuels, must adopt more sustainable practices. Hydrogen, known for its clean combustion and extensive flammability range, presents a viable alternative. Research indicates that hydrogen-powered vehicles consume less fuel and produce lower greenhouse gas emissions [25]. HHO has been shown to enhance engine efficiency, decrease fuel consumption, and lower the emissions of harmful pollutants, including HC, CO, and CO₂, as indicated by various studies. Because hydrogen has a higher and more complete combustion rate than conventional fuels, its addition to combustion engines enhances combustion efficiency. This leads to reduced incomplete combustion and lower production of unburned hydrocarbons (HC) and carbon monoxide (CO) [9,26]. Experimental results showed a 4% reduction in exhaust gas temperature attributed to improved combustion efficiency. Experimental results demonstrated a 4% reduction in exhaust gas temperature attributed to enhanced combustion efficiency, leading to a concomitant reduction in NOx emissions [27]. Furthermore, the study revealed a 6.7% decrease in HC emissions when utilizing gasoline. The introduction of HHO gas resulted in a notable 16.3% improvement in thermal efficiency and a reduction in brake-specific fuel consumption [28,29]. Brown gas, when employed as an auxiliary fuel, demonstrated a 20–30% reduction in fuel consumption and a 3–8% enhancement in thermal efficiency [10,30]. HHO gas in gasoline yielded a 20% reduction in fuel consumption and a 5.7% increase in engine output power, accompanied by decreased NOx, CO, and HC emissions in gasoline engines [27,31]. CO emissions for 1500 CC and 1300 CC engines were reduced to 33% and 24.5%, respectively. HC emissions decreased to 27.4% and 21%, while fuel consumption was lowered to 14.8% and 16.3%. The research indicated increases in output power of 17.9% and 22.4%, as well as improvements in brake thermal efficiency of 15.7% and 19.1% [32,33]. The concentrations of CO and HC decreased by 40% when the plate spacing was increased to 5 mm [34]. HHO gas demonstrated a 16.3% enhancement in fuel consumption efficiency and a 27% increase in power output compared to gasoline [35]. Studies have reported a 20–30% reduction in fuel consumption when utilizing HHO gas [36,37] compared to petrol, a beta cell that produced HHO gasoline at a rate of 0.375L/min-cut fuel use by 17%, HC emissions by 27%, and CO emissions by 27% [38,39]. According to tests, increasing the input power from 2 V to 4 V made the electrolyzer 51.12% more efficient. As the current went from 6 A to 42 A, the gas flow rate went from 137 mL/min to 654 mL/min. A 5 g NaOH electrolyte cell with nineteen neutral plates, four cathodes, and three anodes made 866 mL/min of HHO, which means it works 72.1% of the time as an electrolyzer [40,41]. Previous research [42] has demonstrated that introducing HHO gas into an internal combustion engine can lead to a modest enhancement in brake power, ranging from 2.4% to 2.8%. However, the impact on emissions is more complex, with increases in NOx, reductions in HC, and varying CO and CO₂ levels trends. Previous studies have demonstrated that incorporating 3.8% and 7.5% HHO gas into a Peugeot-1B53318F engine can enhance brake power by 11.2% and 11.7%, respectively, while improving brake thermal efficiency at 1500 and 4000 rpm. However, despite a reduction in HC emissions, these enhancements were accompanied by a significant increase in NOx emissions [43]. Researchers [44] found that adding HHO gas to a Hyundai engine increased thermal efficiency by 5.3–6.9%, but also increased NOx emissions. This study investigated [31] the effects of adding HHO gas to a gasoline engine. Results showed improvements in engine performance, including increased volumetric and thermal efficiency, reduced specific fuel consumption, and lower exhaust gas temperature. Additionally, HHO gas reduced CO, HC, NOx, and CO₂ emissions. Prior studies demonstrate that HHO gas generated by dry electrolyzers provides enhanced performance and improved emission reduction advantages compared to wet electrolyzers. Dry electrolyzers have enhanced thermal efficiency by 4%, air–fuel ratio by 7%, and volumetric efficiency by 5.5% while substantially reducing CO, CO₂, and HC emissions [45]. Including H₂/O₂ in the fuel mixture resulted in a 7.8% reduction in fuel consumption for engine loads exceeding 20%. The HC content decreased by 18%, the concentration of CO declined by 31.8%, and CO₂ emissions were reduced by 30%. The average concentration of NOx decreased by 26% at low engine loads, while it increased by nearly 80% at high loads [28,46]. Incorporating HHO gas with gasoline resulted in a 40% reduction of unburned hydrocarbons in various vehicles, while Fiat models exhibited a nearly 20% decrease. Oxy-hydrogen was supplied indirectly into the intake systems of SI engines to reduce NOx emissions [47,48]. HHO electrolyzers can be classified as dry, wet, or hybrid types. Dry cells can be classified as alpha, beta, or omega [49,50].

This research investigates the feasibility of using vehicle air conditioner drain water as an electrolyte solution to generate HHO gas as a secondary fuel for internal combustion engines. This study assessed the feasibility of utilizing air conditioner drains as a sustainable alternative to distilled water for HHO gas production, focusing on environmental and economic sustainability. The study aims to reduce fuel consumption, increase engine efficiency, reduce greenhouse gas emissions, and conserve potable water. First, different types of gasoline of 80, 92, and 95 octanes were evaluated to determine which provided the best engine torque and power performance. Based on these results, 92-octane fuel was selected as the optimal fuel for further study on the effect of HHO supplementation as a secondary fuel. Different flow rates of HHO gas were mixed with the 92-octane fuel, and the effect of HHO gas concentrations on engine performance was then studied.

2. Materials and Methods

2.1. Development of HHO Gas Dry Generator

HHO gas is composed of hydrogen and oxygen in a ratio of 1:2. In the current study, the production of HHO gas was conducted using the process of water electrolysis. A gas-generating system incorporating pulse-width modulation (PWM) control for temperature, current, and HHO flow rate was utilized. Water reservoir, parallel-cell electrolyzer, bubbler, and wiring were included [49]. A 12 VDC, 60 A battery (Bosch Car Battery-N60L-12/60 AH) served as the power source for the anode and cathode. The dry cell electrolyzer was constructed using square plates measuring 200 mm × 200 mm × 1 mm. The system provided a peak voltage of 12 volts and a peak direct current of 20 amperes. The voltage for each cell was established at 2 volts, with a maximum current of 16 amperes per stack [51,52,53]. An electrolyte solution with a 20 g concentration was utilized as the ion-conducting medium. The constructed cell has a capacity of 1 L for the electrolyte solution, a 3 mm electrode separation, one stack, seven cells, and five neutral plates. Active plates were configured with one negative pole and one positive pole (+5N−). This research investigated the feasibility of replacing distilled water with an electrolyte solution derived from air conditioner condensate. The properties of both solutions were analyzed with an ADWA/AD8000 multiparameter meter, which offers high precision for measuring pH (resolution of 0.01 or 0.001 pH units), conductivity (resolution of 0.01, 0.1, or 1 μS/cm or ppm, and 0.01 or 0.1 mS/cm or ppt), and temperature (resolution of 0.1 °C). Before analysis, a standard domestic water filter collected particulates from air conditioner condensate, specifically the first-stage candle filter. The evaluation of water quality post-filtration demonstrated a significant reduction in contaminant concentrations. Figure 1 presents the pH and total dissolved solids (TDS) measurements for both solutions, with results summarized in

Table 1. Assessment of water quality: TDS and pH between distilled water and air conditioner condensate.

Property	Air Conditioner Condensate	Distilled Water
pH	7.75 Neutral	7.2 Neutral
TDS	22.4 ppm	3 ppm

.

2.2. Fabrication of the HHO Gas Electrolyzer

The rate of HHO gas production is influenced by various factors, including electrode material, electrode geometry, electrode spacing, electrolyte type, electrolyte concentration, and applied current [50]. In this study, HHO gas was generated through water electrolysis using a 12 V DC battery power source. Two electrolyte solutions containing a fixed concentration of 20 g KOH were employed. The solutions differed in the type of prepared water: distilled water and air conditioner condensate. When electrolysis occurs, the electrolyzer’s positive terminal produces H₂ as an anode, and its negative terminal produces O₂ gas as a cathode. Equations (1) and (2) describe the specific anode–cathode reactions between electrode material and geometrical parameters, while (3) measures the electrical energy necessary for the reaction to proceed and are two elements that influence the rate of HHO gas generation. The schematic illustration of the HHO generation process is shown in Figure 2.

2.3. The Input Used to Generate HHO Gas

Under load, the engine’s alternator generated 12 V and separated the cells into stacks. The electrolyzer produced more excellent heat with a higher input voltage. Faraday, Yule Brown, and Bob Boyce used Equation (4) to get the voltage needed for each cell, which came out to be 1.24 V, 1.48 V, 2.0 V, and 3.0 V.

$$\mathrm{I}\mathrm{n}\mathrm{p}\mathrm{u}\mathrm{t} \mathrm{V}\mathrm{o}\mathrm{l}\mathrm{t}\mathrm{a}\mathrm{g}\mathrm{e} \mathrm{P}\mathrm{e}\mathrm{r} \mathrm{C}\mathrm{e}\mathrm{l}\mathrm{l}={\displaystyle \frac{\mathrm{I}\mathrm{n}\mathrm{p}\mathrm{u}\mathrm{t} \mathrm{v}\mathrm{o}\mathrm{l}\mathrm{t}\mathrm{a}\mathrm{g}\mathrm{e} \mathrm{f}\mathrm{r}\mathrm{o}\mathrm{m} \mathrm{b}\mathrm{a}\mathrm{t}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{y} \mathrm{t}\mathrm{h}\mathrm{r}\mathrm{o}\mathrm{u}\mathrm{g}\mathrm{h} \mathrm{e}\mathrm{n}\mathrm{g}\mathrm{i}\mathrm{n}\mathrm{e} \mathrm{a}\mathrm{l}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{n}\mathrm{a}\mathrm{t}\mathrm{o}\mathrm{r}}{\mathrm{N}\mathrm{u}\mathrm{m}\mathrm{b}\mathrm{e}\mathrm{r} \mathrm{o}\mathrm{f} \mathrm{c}\mathrm{e}\mathrm{l}\mathrm{l}\mathrm{s} \mathrm{p}\mathrm{e}\mathrm{r} \mathrm{s}\mathrm{t}\mathrm{a}\mathrm{c}\mathrm{k}}}$$

(4)

This experiment generated HHO gas by varying the current flow between 6 and 16 A. Figure 2 illustrates the production of HHO gas. The efficiency of HHO gas production by the generator is contingent upon the water movement through the system and the current traversing the surface area of the plates. The current traverses all cell areas as it moves across different plates. According to Faraday’s law, a current of 835 A/m² is required [34]. The anode generates hydrogen in an electrolyzer, while the cathode produces oxygen. Faraday’s equation quantifies the production of HHO gas as 1.74 × 10⁻⁷ m³/s per unit area of the water cell. This equation indicates that a current of 1 A sustained for 1 min generates 1.16 × 10⁻⁷ m³/s of hydrogen and 5.80 × 10⁻⁸ m³/s of oxygen. An increase in current directly correlates with increased gas production, as current density is proportional to HHO gas output. Equations (5)–(7) were employed to calculate gas production by Faraday’s law.

$$\mathrm{H}\mathrm{y}\mathrm{d}\mathrm{r}\mathrm{o}\mathrm{g}\mathrm{e}\mathrm{n}:{\mathrm{N}}_{{\displaystyle \frac{\mathrm{c}}{\mathrm{s}}}}\times \mathrm{N}\mathrm{s}\times \mathrm{A}\mathrm{s}\times 0:1.16\times {10}^{-7} {\mathrm{m}}^3/\mathrm{s}\times 28:3$$

(5)

$$\mathrm{O}\mathrm{x}\mathrm{y}\mathrm{g}\mathrm{e}\mathrm{n}:{\mathrm{N}}_{{\displaystyle \frac{\mathrm{c}}{\mathrm{s}}}}\times \mathrm{N}\mathrm{s}\times \mathrm{A}\mathrm{s}\times 0:5.80\times {10}^{-8} {\mathrm{m}}^3/\mathrm{s}\times 28:3$$

(6)

$$\mathrm{H}\mathrm{H}\mathrm{O} \mathrm{G}\mathrm{a}\mathrm{s}:{\mathrm{N}}_{{\displaystyle \frac{\mathrm{c}}{\mathrm{s}}}}\times \mathrm{N}\mathrm{s}\times \mathrm{A}\mathrm{s}\times 0:1.74\times {10}^{-7} {\mathrm{m}}^3/\mathrm{s}\times 28:3$$

(7)

NC/S stands for the number of cells per stack, NS for the number of stacks, and AS for the working voltage per stack. The amounts of hydrogen, oxygen, and HHO gas created by one ampere of current for one minute are 1.16 × 10⁻⁷ m³/s, 5.80 × 10⁻⁸ m³/s, and 1.74 × 10⁻⁷ m³/s, respectively.

2.4. Cell Efficiency

The efficiency of an electrolyzer cell can be determined by dividing the total energy created inside it by the total electrical energy fed into it. This is achieved by multiplying the output mass flow rate by the calorific value of hydrogen. Equation (10) [35] can help determine how well the electrolyzer cell works. Equation (8) reveals how much energy is created, and Equation (9) shows how much power is needed overall.

$$\mathrm{The} \mathrm{energy} \mathrm{gained}=\mathrm{the} \mathrm{mass} \mathrm{flow} \mathrm{rate}\times \mathrm{the} \mathrm{hydrogen}’\mathrm{s} \mathrm{calorific} \mathrm{value}$$

(8)

$$\mathrm{T}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l} \mathrm{e}\mathrm{n}\mathrm{e}\mathrm{r}\mathrm{g}\mathrm{y}={\mathrm{V}}_{\mathrm{i}}\times {\mathrm{A}}_{\mathrm{c}}\times {\mathrm{N}}_{\mathrm{c}}$$

(9)

$${\eta }_{\mathrm{c}\mathrm{e}\mathrm{l}\mathrm{l}}=\mathrm{T}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l} \mathrm{e}\mathrm{n}\mathrm{e}\mathrm{r}\mathrm{g}\mathrm{y} \mathrm{a}\mathrm{c}\mathrm{q}\mathrm{u}\mathrm{i}\mathrm{r}\mathrm{e}\mathrm{d}/\mathrm{T}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l} \mathrm{e}\mathrm{n}\mathrm{e}\mathrm{r}\mathrm{g}\mathrm{y} \mathrm{e}\mathrm{x}\mathrm{p}\mathrm{e}\mathrm{n}\mathrm{d}\mathrm{e}\mathrm{d}$$

(10)

V_i refers to the input operating voltage applied to the system. A_c represents the input operational amperes per stack, indicating the electrical current flowing through each individual stack. N_c denotes the total number of stacks utilized in the setup.

3. Experimental Procedure

3.1. Produce HHO Gas

A 12 V DC battery was connected to the electrolyzer via a current modulator, allowing input current and temperature adjustments through PWM. The flow rate of HHO was determined by assessing the volume of water gathered in a graduated cylinder within a defined time frame. The cell was set up with a voltage of 12 V, a current source of 6 A, 10 A, 14 A, and 16 A, and a catalyst concentration of 20 g KOH to explore the obtained flow rate at the various currents. The highest flow rate, 480 mL/min, was obtained at 16 A. Using a bubble tank and a flame arrester, a 1 L mix of pure water and a sample of air conditioner condensate, each with 20 g KOH, were added to a dry electrolytic cell to improve current flow and stop backflow.

3.2. Engine Testing Equipment

The Spark Ignition Engine (SIE) engine employed in this study is a Daewoo 160CC 4-stroke, 4-cylinder, air-water-cooled engine with 76.5 mm Bore × 81.5 mm Stroke with a peak output of 63 kW at 5800 rpm and a maximum torque of 130 Nm at 3400 rpm. The engine was coupled with a hydraulic dynamometer (LABTECH, ET-DHA-1) to control speed and torque. Figure 3 illustrates a schematic representation of the experimental configuration. The air surge tank’s side was fitted with a 1 cm diameter hole to measure the intake air mass flow rate. The exact volume of 20 cm³ was delivered using a gasoline burette. After a cautious insert, the exhaust gas analyzer probe was placed into the engine’s exhaust system. Next to the exhaust valve was where the exhaust measuring port was placed. Emissions were quantified utilizing a Sauermann F5000-6 gas analyzer. The Sauermann F5000-6 has a measuring range of CO₂, HC, CO, NOx, and O₂ of 0–20%, 0–10,000 ppm, 0–15%, 0–5000 ppm, and 0–0.25%, with an accuracy of ±3%, ± 3 to ±8 ppm (based on the range), ±3%, ±4 to ±5 ppm, and 0.1%, respectively. The exhaust gas temperature is measured using a K-type thermocouple. Experiments have shown a range of data on the system’s behavior using specialized measuring instruments. Some experiments have been conducted under suitable conditions to verify the validity of the results. All tests were performed three times to evaluate repeatability errors. The engine was subjected to a diverse load test at a constant rotational speed of 3000 rpm. Data were collected following the stabilization of the system. Pure gasoline with octane ratings of 80, 92, and 95 was initially utilized to determine the optimal fuel for the engine. The optimized gasoline was blended with HHO gas generated from air conditioner drain water to assess its impact on engine efficiency and emissions.

The volumetric flow rate of gasoline at each load was calculated to assess the effect of HHO gasoline addition on fuel consumption. This was achieved by measuring the time taken to consume a fixed volume of gasoline under two conditions: with and without a constant HHO flow rate. Equations (11) and (12) were employed to calculate the flow rate in each case:

$${\mathrm{M}}_{\mathrm{g}\mathrm{a}\mathrm{s}\mathrm{o}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}}={\rho }_{\mathrm{g}\mathrm{a}\mathrm{s}\mathrm{o}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}}\times {\mathrm{V}}_{\mathrm{g}\mathrm{a}\mathrm{s}\mathrm{o}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}}$$

(11)

$${\mathrm{m}}_{\mathrm{g}\mathrm{a}\mathrm{s}\mathrm{o}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}}+{\mathrm{m}}_{\mathrm{H}\mathrm{H}\mathrm{O}}={\rho }_{\mathrm{g}\mathrm{a}\mathrm{s}\mathrm{o}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}}\times {\mathrm{V}}_{\mathrm{g}\mathrm{a}\mathrm{s}\mathrm{o}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}}+{\rho }_{\mathrm{H}\mathrm{H}\mathrm{O}}\times {\mathrm{V}}_{\mathrm{H}\mathrm{H}\mathrm{O}}$$

(12)

where m_gasoline and m_HHO denote the mass flow rates of gasoline and HHO, respectively. The volumetric flow rate of HHO was maintained at a constant 0.480 LPM (V_HHO), while the volumetric flow rate of gasoline (V_gasoline) was varied. The gasoline and HHO gas densities were V_gasoline = 750.3 kg/m³ and ρ_HHO = 0.55 kg/m³, respectively. The chemical formula for gasoline is C8H18. The hydrogen composition of the gasoline is 15.8%, while the HHO is 11%. The BSFC and BTE values for gasoline in conjunction with HHO are obtained from Equations (13)–(15).

$$\mathrm{B}\mathrm{S}\mathrm{F}\mathrm{C}={\displaystyle \frac{m_{\mathrm{f}}}{\mathrm{B}\mathrm{P}}}={\displaystyle \frac{m_{\mathrm{g}\mathrm{a}\mathrm{s}\mathrm{o}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}}}{\mathrm{B}\mathrm{P}}}+{\displaystyle \frac{m_{\mathrm{H}\mathrm{H}\mathrm{O}}}{\mathrm{B}\mathrm{P}}}={\displaystyle \frac{{\mathrm{V}}_{\mathrm{g}\mathrm{a}\mathrm{s}\mathrm{o}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}} {\rho }_{\mathrm{g}\mathrm{a}\mathrm{s}\mathrm{o}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}}}{\mathrm{B}\mathrm{P}}}+{\displaystyle \frac{{\mathrm{V}}_{\mathrm{H}\mathrm{H}\mathrm{O}} {\rho }_{\mathrm{H}\mathrm{H}\mathrm{O}}}{\mathrm{B}\mathrm{P}}}$$

(13)

$$\mathrm{B}\mathrm{T}\mathrm{E}={\displaystyle \frac{3600}{\mathrm{B}\mathrm{S}\mathrm{F}\mathrm{C}.\times \mathrm{L}\mathrm{H}\mathrm{V}}}100$$

(14)

$$\mathrm{L}\mathrm{H}\mathrm{V}={\displaystyle \frac{m_{\mathrm{g}\mathrm{a}\mathrm{s}\mathrm{o}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}} {\mathrm{L}\mathrm{H}\mathrm{V}}_{\mathrm{g}\mathrm{a}\mathrm{s}\mathrm{o}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}}+m_{\mathrm{H}\mathrm{H}\mathrm{O}} {\mathrm{L}\mathrm{H}\mathrm{V}}_{\mathrm{H}\mathrm{H}\mathrm{O}}}{m_{\mathrm{g}\mathrm{a}\mathrm{s}\mathrm{o}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}}+m_{\mathrm{H}\mathrm{H}\mathrm{O}}}}$$

(15)

Q represents the fuel consumption flow rate measured in kg/s, while BP denotes the output brake power expressed in kW. The mass flow rates of gasoline and HHO gas are m_gasoline and m_HHO. The gasoline and HHO gas volumetric flow rates are V_gasoline and V_HHO (0.480 LPM). The densities of gasoline (ρ_gasoline = 0.771 kg/m³) and HHO gas (ρ_HHO = 0.55 kg/m³) are given. A gasoline–HHO combination has a lower heating value (LHV). Gasoline has a lower heating value of 42,000 kJ/kg. The lower heating value of hydrogen is 120,000 kJ/kg. The engine’s crankshaft was loaded with required loads from zero to full-load using a hydraulic dynamometer. The engine was originally run on gasoline at 0.9, 1.8, 2.6, and 3.5 kW. After validating the air conditioning drain water’s HHO gas generation efficiency, the engine was run with it. The engine speed was set to 3000 rpm in all conditions. Under these conditions, torque and power were measured, and the fuel quantity was modified and calibrated to match the predicted load.

4. Results and Discussions

The experiment sought to assess the efficacy of an electronic fuel injection engine augmented with hydrogen generated from an electrolysis cell using air conditioner condensate. The outcomes were as follows.

4.1. Temperature Versus Time

Figure 4 shows the temperature variation over time at various currents of 6, 10, 14, and 16 A for both distilled water (DW) and air conditioner drain (ACD) water. An increase in the current supplied to the system results in a corresponding temperature rise, as higher currents enhance ion transfer within the cell. An increase in current enhances the electron flow, which drives ion transfer in the electrolyte, contributing to heat generation. The electrolyte solution in the cell comprises only 20 g/L, leading to an increased temperature. The recorded measurement pertained to 100 mL of water displacement from the biuret. The displacement duration was documented for later computations. The temperature increased from a minimum of 26 °C to a maximum of 45 °C with the increased temperature, as shown in Figure 4. The minimum temperature was observed at the commencement of the experiment. In contrast, the maximum temperature was recorded after 60 min of continuous electrolyzer operation. The current under this condition measured 16 A. At this temperature, air conditioner drain water has comparable properties to distilled water and can be used effectively. The electrolyte undergoes boiling and evaporation when using distilled water. In contrast, air conditioner drain water compensates for this loss, helping to maintain a lower temperature. The air conditioner drain water system eliminates the need for an additional cooling mechanism.

4.2. Production Range for HHO Compared to Current Supply

Figure 5 shows a direct relationship between the electric current intensity and the HHO gas production rate from distilled and air conditioner drain water. The results indicate that both types of water exhibited identical production rates under all experimental conditions, 6, 10, 14, and 16 A. This indicates that air conditioner drain water can be an effective alternative to distilled water in HHO gas production.

4.3. The Influence of Fuel Types on the Efficacy of Electronic Fuel Injection Engines

Figure 6a,b comprehensively show the engine torque and power characteristics across three fuels (80, 92, and 95), focusing on a gasoline engine with electronic fuel injection and a compression ratio of 11:1. The results evaluate the impact of different fuels on engine performance indicators, which are essential for evaluating overall engine efficiency. The results show that 92 gasoline outperforms the other evaluated fuels, with a maximum torque of 191 Nm and a maximum power output of 113 kW. The data indicate that 92 gasoline facilitates excellent combustion and energy conversion efficiency in engines equipped with electronic fuel injection and a relatively high compression ratio. The superior performance of 92 gasoline is due to its octane rating, which enables it to withstand more excellent compression without premature detonation. This characteristic is particularly beneficial for engines with high compression ratios, as it improves energy extraction from the air–fuel mixture while ensuring smooth operation. The results confirm the compatibility of 92 gasoline with electronic fuel injection systems, which precisely control the air–fuel mixture and ensure excellent combustion under various load conditions.

4.4. Brake-Specific Fuel Consumption (BSFC)

Figure 7 illustrates that augmenting the hydrogen flow rate, facilitated by elevated electrical current, decreases gasoline use. At the maximum HHO flow rate of 480 mL/min (16 A), fuel economy is enhanced with diminished brake-specific fuel consumption (BSFC) at all engine loads. This illustrates the capability of HHO-enriched gasoline to enhance engine performance and fuel efficiency. The reduction in BSFC is due to HHO’s ability to enhance fuel–air mixing, increase oxygen levels, and accelerate combustion. Hydrogen’s high flame speed and more comprehensive flammability range promote efficient and complete combustion, while its higher calorific value enhances power output for the same amount of fuel. The documented 8.7% decrease in BSFC aligns with prior research, yielding advantages like diminished fuel expenses and fewer pollutants [25,27]. Significantly, these enhancements do not necessitate substantial engine alterations, underscoring the practicality of using HHO gas in current systems.

4.5. Brake Thermal Efficiency

Figure 8 presents a gasoline engine’s braking thermal efficiency (BTE) at various HHO flow rates (various currents). The findings indicate that increasing HHO increases combustion efficiency, improving overall engine performance. The increased HHO concentration, rapid flame propagation, and improved fuel–air mixing associated with HHO enhance brake thermal efficiency (BTE). The maximum observed enhancement in thermal efficiency was 7.9% at the obtained maximum HHO flow of 480 mL/min at 16 A. The findings align with previous studies [9,28,31].

4.6. The Temperature of the Exhaust Gas (EGT)

Figure 9 illustrates the effect of HHO gas supplementation at various flow rates on exhaust gas temperature (EGT) at various engine loads. The results demonstrate a notable reduction in EGT due to the enhanced combustion efficiency facilitated by HHO. The increased oxygen levels, rapid flame propagation, and improved fuel–air mixing associated with HHO also decrease EGT. Reducing exhaust gas temperature indicates enhanced thermal efficiency and decreased fuel consumption. The highest observed reduction in EGT was 7.6%, aligning with previous research [30,37,46].

4.7. Volumetric Efficiency

Figure 10 shows the effects of different HHO flow rates on volumetric efficiency across different engine loads. Volumetric efficiency showed a slight improvement with increasing HHO flow due to its superior combustion characteristics despite higher cylinder temperatures and lower air density under heavy loads. Including HHO gas effectively addresses the constraints of low air density by improving air–fuel fusion and increasing the combustion rate, facilitating optimal mixture use. A 5.8% improvement in volumetric efficiency was observed at the highest HHO flow rate (480 mL/min), consistent with previous studies [46,48]. This enhancement resulted from the broader ignition spectrum of HHO gas, faster flame propagation, and a more significant contribution of oxygen, all of which facilitated more complete combustion. The results demonstrated that HHO gas is a potent method for improving engine performance, particularly under high-load conditions.

4.8. Air–Fuel

Figure 11 illustrates the impact of variation of HHO gas flow rates on the air–fuel ratio (air to fuel in a combustion process) for various engine loads. Increased fuel consumption led to a reduced air–fuel ratio, attributed to the enhanced combustion efficiency facilitated by HHO. The increased oxygen levels and improved fuel–air mixing associated with HHO enabled this modification. Adding HHO enhanced the lean flammability limit of the gasoline–air mixture, resulting in a maximum reduction of 10.5% in the air–fuel ratio. The findings align with previous research [9,34].

4.9. Emission of Carbon Monoxide

Figure 12 shows how adding HHO gas affects carbon monoxide emissions at varying engine loads. According to the results, using HHO instead of gasoline significantly reduces CO emissions. Increased combustion efficiency, a consequence of faster flame propagation of HHO and higher oxygen levels, is responsible for the improvement. Further reduced CO emissions are achieved by adding HHO, which results in a thinner air–fuel combination. Consistent with previous research [9,35], the maximum measured reduction in CO emissions was 18%.

4.10. Emissions of Carbon Dioxide

Figure 13 shows the correlation between engine load and CO₂ emissions for gasoline at various HHO flow rates. The results show that using HHO as a gasoline additive significantly reduces CO₂ emissions. The enhanced performance is a direct outcome of the faster flame propagation and higher combustion efficiency offered by HHO. Consistent with previous research [9,25,38], the maximum measured reduction in CO₂ emissions was 9.2%.

4.11. Emission of Nitrogen Oxides

Adding HHO gas leads to a 12.5% rise in nitrogen oxide (NOx) emissions, as shown in Figure 14. This increase occurs because HHO gas raises the combustion temperature and adds more oxygen radicals, which help the fuel burn and create conditions for NOx. The high flame speed and wide range of flammability of hydrogen make combustion better and increase the production of thermal NOx, which is in line with the Zeldovich mechanism and previous research [42,45]. NOx emissions are concerning as they contribute to smog, ozone formation, and health issues. While HHO gas improves fuel efficiency and reduces CO and HC emissions, addressing this NOx increase is critical. Mitigation strategies include optimizing engine controls to lower peak cylinder temperatures and implementing after-treatment systems like selective catalytic reduction and exhaust gas recirculation.

4.12. Emission of Hydrocarbons

Figure 15 shows how adding HHO gas affects the emissions of hydrocarbons (HCs). The use of HHO led to a significant reduction in HC concentrations, even though HC emissions increased with increased engine loads. Because of the oxygen in HHO and the fact that flames spread more quickly, combustion efficiency is increased, leading to improvement. Hydrocarbon emissions are partially reduced because HHO gas has a broader spectrum of flammability. Consistent with previous studies [35], the observed decrease in HC emissions reached 9%.

5. Conclusions

This study explored using oxy-hydrogen (HHO) gas from vehicle air conditioner drain water as a secondary fuel to improve engine efficiency, lower greenhouse gas emissions, and reduce fuel consumption. Different grades of gasoline (80-, 92-, and 95-octane) were evaluated to determine their performance under various loads and power, identifying 92-octane as the most efficient. Then, 92 octane gasoline was boosted with HHO gas at flow rates of 50, 248, 397, and 480 mL/min, and the effects on fuel consumption, thermal efficiency, volumetric efficiency, greenhouse gas (CO, CO₂, and HC) emissions, and NOx emissions were examined. The results indicated that increasing HHO flow rates significantly enhanced engine performance and reduced greenhouse gas emissions. At the maximum flow rate (480 mL/min), fuel consumption decreased by 8.7%, although thermal and volumetric efficiency improved by 5.5% and 7.9%, respectively. Significant reductions were recorded in CO, CO2, and HC emissions by 18%, 9.2%, and 9%, respectively. However, NOx emissions increased by 12.5%, possibly due to the higher combustion temperatures resulting from hydrogen incorporation. The findings suggest that adding HHO generated from air conditioning drain water to 92-octane gasoline can make engines run better and use less fuel, saving energy and lowering greenhouse gas emissions worldwide. The high NOx emissions highlight a significant concern that requires further mitigation study. This technology indicates a promising advance in sustainable energy solutions for internal combustion engines, with prospects for future improvement and broader application.

Ultimately, this study raised several challenges, including accurate cylinder pressure measurement, optimal mixing ratio of HHO gas with conventional fuel, and precise ignition timing. Reducing nitrogen oxide (NOx) emissions also emerged as a significant concern. Therefore, further research is needed to address these challenges.