An Evaluation of the Effect of Fuel Injection on the Performance and Emission Characteristics of a Diesel Engine Fueled with Plastic-Oil–Hydrogen–Diesel Blends

Abstract

Fuelled engines serve as prime movers in low-, medium-, and heavy-duty applications with high thermal diesel efficiency and good fuel economy compared to their counterpart, spark ignition engines. In recent years, diesel engines have undergone a multitude of developments, however, diesel engines release high levels of NOx, smoke, carbon monoxide [CO], and hydrocarbon [HC] emissions. Due to the exponential growth in fleet population, there is a severe burden caused by petroleum-derived fuels. To tackle both fuel and pollution issues, the research community has developed strategies to use economically viable alternative fuels. The present experimental investigations deal with the use of blends of biodiesel prepared from waste plastic oil [P] and petro-diesel [D], and, to improve its performance, hydrogen [H] is added in small amounts. Further, advanced injection timings have been adopted [17.5° to 25.5° b TDC (before top dead centre)] to study their effect on harmful emissions. Hydrogen energy shares vary from 5 to 15%, maintaining a biodiesel proportion of 20%, and the remaining is petro-diesel. Thus, the adopted blends are DP20 ((diesel fuel (80%) and waste plastic biofuel (20%)), DP20H5 (DP20 (95%) and hydrogen (5%)), DP20H10 (DP20 (90%) and hydrogen (10%)), and DP20H15 (DP20 (85%) and hydrogen (15%)). The experiments were conducted at constant speeds with a rated injection pressure of 220 bar and a rated compression ratio of 18. The increase in the share of hydrogen led to a considerable improvement in the performance. Under full load conditions, with advanced injection timings, the brake-specific fuel consumption had significantly decreased and NOx emissions increased.

1. Introduction

In light of the increasing popularity of electric and hybrid cars as viable alternatives to internal combustion engines, it has been observed that IC (internal combustion) engines remain a dependable and cost-effective power generation mechanism for both automotive and stationary purposes. Modern businesses and cars emit exhaust gases that warm the atmosphere and increase nitrogen oxide, carbon dioxide, hydrocarbon, and carbon monoxide levels. As this may cause major environmental issues, it must be handled promptly. Rapid diesel consumption and exhaust gas emissions continue to burden the environment. Compression ignition engines have proven to be efficient, reliable, sturdy, and robust in long-distance transportation, heavy-duty engines, machines, and many carriers. Compression ignition engines are very polluting; hence, attempts are needed to combine these qualities into a trademark engine with low exhaust gas emissions for a renewable, less polluting transportation engine [1,2].

Jafari et al. (2021) investigated the effects of advanced fuel injection timing (AFIT) from −6 to −16 aTDC (after top dead centre) on a direct injection engine fuelled by hydrogen, diesel, and carbon monoxide in comparison to IC engines of alternative sources. Compared to the baseline, PDC (Pure Diesel Combustion), DSC20 (Diesel to syngas energy (20%)), and DSC40 (diesel to syngas energy (40%)) blends, the thermal efficiency of the engine improved by 2.76%, 1.9%, and 1.34% with the DSC20 and DSC40 blends. On the other hand, heat transfer loss grew [3]. Paparao et al. (2023) demonstrate the effects of compression ratio (16.5 to 18.5), fuel injection pressure (220 to 240 bar), and injection timing (24.5° to 27.5° before top dead centre) when hydrogen is blended with biodiesel and diesel. The results demonstrated a 6.6% increase in thermal efficiency with hydrogen-JME20 (Jatropha biodiesel–diesel blend) at 240 bar, 26.5° b TDC, and 18.5 CR (compression ratio), but lower emissions of smoke, carbon monoxide, and hydrocarbons [4]. Channapattana et al. (2023) studied the effects of injection timings ranging from 23° b TDC to 27° b TDC with azadirachta indica biodiesel containing nickel oxide nanoparticles (25 ppm and 50 ppm) in a diesel engine. They discovered that the NB25 blend reduced fuel consumption and radiation energy loss by 2.3% and 3.1% for 23° b TDC to 27° b TDC, respectively [5].

The study conducted by Arulkumar and Vijayaragavan (2023) examined the impact of hydrogen fuel mixtures containing diesel and Calophyllum inophyllum oil (CIO) on a single cylinder diesel engine operating at 75% and 100% engine capacity. A 20% blend of CIO with hydrogen was found to increase brake thermal efficiency by 5.34%, reduce CO and HC emissions by 14.8 and 90.1%, and decrease particulate emissions by 32.6%, compared to diesel fuel alone [6]. The study conducted by Kakran et al. (2023) examined the impact of hydrogen fuel mixtures containing diesel on a single cylinder diesel engine operating at different load and compression ratios. A blend of hydrogen–diesel was found to increase brake thermal efficiency by 6.38% and reduce specific fuel consumption and volumetric efficiency by 4.8 and 1.89% compared to diesel fuel alone [7]. Vargun and Ozsezen (2023) investigated the effect of alcohol–diesel fuel mixes on a single cylinder diesel engine with a fuel injection. The findings revealed that with an advanced fuel injection time, the cylinder pressure rose, the heat release rate increased, and the combustion duration decreased as the alcohol content increased. With the usage of mixed gasoline, the engine’s knocking propensity worsened [8].

Gultekin et al. (2023) evaluated the impact of a hydrogen–diesel mix on a diesel engine at various loads (3, 4.5, 9, 7.5, 9 N.m) and intake valve lifts (4.0, 4.46, 4.9 mm) at 1850 rpm. They discovered that a 7.0% hydrogen energy share reduced soot emissions by 40.0% and CO emissions by 33.0% [9]. Paneerselvam et al. (2023) investigated the influence of a hydrogen and hydroxyl biodiesel mix containing Melia dubia and peppermint oil on a diesel engine at different compression ratios (17.5, 19.5, and 21.5) with exhaust gas recirculations of EGR10 (exhaust gas recirculation percentage), EGR15, and EGR20% at 19°, 21°, and 23° CA (crank angles) at 1500 rpm. They observed that a CR of 19.5 and a CA of 23° with 15% hydrogen increased engine performance [10]. Chaurasiya et al. (2022) studied the effect of a hydrogen, diethyl ether, biodiesel, n-butanol, and diesel mixture on a diesel engine at various advance fuel injection timings of 17.5° 20.0°, 22.2°, 25.5°, 27.5°, and 30.5° CAs at 1500 rpm. They discovered that cylinder pressure rose with advanced injection time and that the 5%H95%SMA mix performed better than the other tested blends [11]. Yousefi et al. (2022) used Converged CFD to evaluate the effects of ammonia energy sharing with diesel fuel at varying advanced fuel injection times on engine performance and emission characteristics using the Caterpillar 3401 engine model. The findings revealed that using ammonia at a low flame speed reduced NOx emissions by 58.8% and indicated thermal efficiency [12].

The literature findings suggest that there are few works which focus on biodiesel or plastic pyrolysis; it was evident from the findings that the waste plastic oil was used as an equivalent to conventional fuel. However, since climatic pollution has become quite a significant aspect, especially due to the heavy usage of fossil fuels, research which orients around clean energy is a necessity. The present work explores hydrogen as a supplement in order to not only better emission characteristics but also improve performance specifics.

The evaluations in this study were carried out on a direct injection diesel engine with a specification single cylinder, four stroke compression ignition engines fuelled with 20% waste-plastic oil biofuel, 80% diesel fuel, and 5%, 10%, and 15% hydrogen fuel, which, when combined, are referred to as DP20, DP20H5, DP20H10, and DP20H15 (waste-plastic oil biofuel, diesel, and hydrogen mixtures) at different injection timings with a full load. The outcomes were compared to DP20 mix samples. The research looked at the performance, combustion, and emission characteristics of several blends with advanced fuel injection timings of 17.5, 19.5, 21.5, 23.5, and 25.5° b TDC (before top dead centre). The effect of various advanced fuel injection timings on cylinder pressure, emitted heat, ignition delay, pressure increase rate, fuel consumption, thermal efficiency, smoke emission, PM emission, and NOx emissions was measured.

2. Materials and Methods

The hydrogen–diesel fuel mix employed in the research, as well as its physical and chemical characteristics, are described in

Table 1. Fuel properties of test fuel [12].

Fuel	Hydrogen	Waste Plastics Oil	Diesel
Density (kg/m3)	0.08	884.0	830
Lower calorific value (MJ/kg)	120	43.0	42.5
Kinematic viscosity (mm2/s) @40 °C	0.0083	3.64	3.0
Sulphur Content	00	0.03–0.35% [14]	10 ppm (~0.001%)
Cetane number	5–10	50	48–52

. The EN590 (European Nations standard for all automotive diesel fuel) standard applies to the diesel fuel [13]. The hydrogen fuel was kept in high-purity cylinders that were compressed to 200 bar. To assure accuracy, the first tests were carried out using diesel fuel repeatedly, and the outcomes of these experiments were published. The hydrogen energy ratio was calculated based on the amount of fuel used in these tests. In this investigation, dual fuel mode tests were conducted with varying degrees of engine load while using hydrogen at 5 lpm (litres per minute), 10 lpm, and 15 lpm. Using Equation (1), we can calculate the ratio of hydrogen energy contribution to total energy. The fraction of hydrogen dynamism in the energy portfolio may be calculated using Equation (1) [14,15]. The fuels used in this investigation were hydrogen and diesel, with 5%, 10%, and 15% of hydrogen energy provided. Figure 1 depicts a mixture of 20% waste plastics, oil, biofuel, and diesel fuel.

$$\mathrm{H}\mathrm{y}\mathrm{d}\mathrm{r}\mathrm{o}\mathrm{g}\mathrm{e}\mathrm{n} \mathrm{e}\mathrm{n}\mathrm{e}\mathrm{r}\mathrm{g}\mathrm{y}={\displaystyle \frac{\mathrm{M}\mathrm{a}\mathrm{s}\mathrm{s} \mathrm{f}\mathrm{l}\mathrm{o}\mathrm{w} \mathrm{r}\mathrm{a}\mathrm{t}\mathrm{e} \mathrm{o}\mathrm{f} {\mathrm{H}}_2\times \mathrm{L}\mathrm{H}\mathrm{V} \mathrm{o}\mathrm{f} {\mathrm{H}}_2}{\mathrm{M}\mathrm{a}\mathrm{s}\mathrm{s} \mathrm{f}\mathrm{l}\mathrm{o}\mathrm{w} \mathrm{r}\mathrm{a}\mathrm{t}\mathrm{e} \mathrm{o}\mathrm{f} {\mathrm{H}}_2\times \mathrm{L}\mathrm{H}\mathrm{V} \mathrm{o}\mathrm{f} {\mathrm{H}}_2+\mathrm{M}\mathrm{a}\mathrm{s}\mathrm{s} \mathrm{f}\mathrm{l}\mathrm{o}\mathrm{w} \mathrm{r}\mathrm{a}\mathrm{t}\mathrm{e} \mathrm{o}\mathrm{f} \mathrm{d}\mathrm{i}\mathrm{e}\mathrm{s}\mathrm{e}\mathrm{l}\times \mathrm{L}\mathrm{H}\mathrm{V} \mathrm{o}\mathrm{f} \mathrm{d}\mathrm{i}\mathrm{e}\mathrm{s}\mathrm{e}\mathrm{l}}}$$

(1)

2.1. Experimental Setup

The objective of the experimental research is to evaluate the performance, combustion, and emissions characteristics of a direct injection compression ignition (DICI) engine using a combination of hydrogen and diesel fuel as the power source. The experimental setup included the connection of a diesel engine, with a solitary cylinder, a four-stroke operation, and water cooling equipment to a hydrogen cylinder, as seen in Figure 2.

Table 2. Experimental setup.

Parameter	Value
Bore/stroke	87.5 mm/110 mm
Compression ratio	18:1
Engine stroke/cylinder	4/1
Engine operating	1500 rpm
Injection pressure	Higher of 220 bar
Injection timing	19–26.0° b TDC
Cooling system	Water
Power	5.2 kW

presents the configuration features of the diesel engine. The use of an eddy current dynamometer involves its connection to the engine control unit (ECU) for the purpose of regulating a range of engine parameters. Additionally, it is linked to the engine in order to exert a load. The AVL DIGAS-444 (flue gas analyser), AVL India Pvt. Ltd., Gurugram, India, was used to conduct an exhaust emission analysis.

Table 3. Uncertainty.

Limits	Uncertainty
BTE	±2.0%
SFC	±2.0%
HRR	±1.0%
CO2	±0.2%
CO	±0.2%
O2	±0.15%
HC	±0.15%
NO	±0.2%
Smoke meter	±1.0%
Temperature sensor	±0.5%
Pressure sensor	±1.0%
Speed indicator	±0.2%
Load indicator	±0.2%
Encoder	±0.2%

displays the attributes of the flue gas analyser. The measurement of combustion pressure was conducted using a Piezotronics sensor, while the crank angle was monitored using a Kubler sensor. Additionally, the fuel flow rate was determined using a Yokogawa sensor. Temperature data were collected by means of K-type thermocouples that were strategically placed throughout the engine configuration. The engine speed, as seen on a digital display, was presented in units of revolutions per minute (rpm). The use of a high-pressure pump was implemented in order to provide diesel fuel to the common rail injection system at an elevated pressure. The primary responsibility of the high-pressure pump was to provide diesel to the common rail injection system, irrespective of the system’s load conditions. The pump was responsible for extracting diesel fuel from the fuel tank and then filtering it. The solenoid valve regulated the amount of diesel supplied to the loading situation. Two manual procedures, namely the burette and stopwatch, were used to measure the flow rate of the diesel. The burette was directly linked to the fuel tank for this purpose. Following a duration of 10 min at an engine speed of 1500 revolutions per minute, the engine was allowed to attain a state of steady-state combustion. Subsequently, the collection of performance and emission data was conducted at full load (10 kg for the engine). The engine parameters were calculated from data provided by ‘enginesoft’ software 9.0.

Hydrogen energy–share ratios were experimentally examined in conjunction with diesel fuel over a range of engine loads. During the suction stroke, a consistent flow of hydrogen was supplied to the intake manifold, gradually displacing the anticipated volume of air. The intake manifold of the car generated a homogenous blend of hydrogen and air. The pressure regulator was used to decrease the high-pressure hydrogen inside the cylinder to a level of 2 bars. Prior to introducing hydrogen into the system, a flame arrester was put at the intake manifold in order to prevent the occurrence of explosions and backfires. In order to mitigate the accumulation of excessive pressure, the flame arrestor was equipped with a pressure release valve. There exist two distinct categories of non-return valves: the first is positioned before to the entry of the input manifold, while the second is set before the entrance of the flow meter. A hydrogen flow meter is used for the purpose of controlling the magnitude of hydrogen flow.

2.2. Uncertainty of Experiment

There are several factors that might contribute to the occurrence of experimental uncertainty. One of the challenges encountered in this field of research is to the presence of uncertainties arising from the use of various measuring instruments to assess diverse attributes. Equation (2) provides an estimation of the comprehensive uncertainty (μ) pertaining to the experiment, taking into account distinct uncertainties (π1, π2… πn) connected with various structures. Table 3 presents the errors associated with parameter estimates, as outlined in references [16,17,18]. Table 3 presents the degree of uncertainty associated with each of the measured quantities. The conducted tests yielded a comprehensive measure of uncertainty, reaching a maximum value of 3.4%.

Uncertainty (π) = Square root of [(CO₂)² + CO)² + O₂)² + (HC)² + (NO)² + (BTE)² + (SFC)² + (HRR)² + (smoke)² +(temperature)² + (pressure)² + (load)² + (crank encoder)²].

(2)

π = Square root of [(2.0)² + 2.0)² + 1.0)² + (0.2)² + (0.2)² + (0.15)² + (0.15)² + (0.2)² + (1.0)² + (0.5)² + (1.0)² + (0.2)² + (0.2)² + (0.2)²]

3. Results and Discussion

3.1. Brake Thermal Efficiency

The term “brake thermal efficiency” (BTE) pertains to the ratio of power input supplied to the engine to the power output generated for braking purposes. Figure 3 depicts the brake thermal efficiency (BTE) at various injection timings ranging from 17.5 to 27.5° before top dead centre (b TDC) under full load engine conditions (10 kg) [19,20]. The BTE values are shown for multiple fuel compositions, including 100% diesel (D100), 20% waste-plastic oil biofuel (DP20), 5% hydrogen blended with 20% waste-plastic oil biofuel (DP20H5), 10% hydrogen blended with 20% waste-plastic oil biofuel (DP20H10), and 15% hydrogen blended with 20% waste-plastic oil biofuel (DP20H15). Typically, the brake thermal efficiency (BTE) exhibits an increase in correspondence with the augmentation of the engine load. This implies that the engine exhibits improved performance in conditions of increased load [21]. The graphical representation indicates that the brake thermal efficiency (BTE) of the DP20H5, DP20H10, and DP20H15 engines surpasses that of the D100 engine across all tested situations. According to previous research findings, the addition of 15% hydrogen to a mix of waste-plastic oil biofuel and diesel fuel has been shown to result in the greatest brake thermal efficiency (BTE) of 37.08%. In comparison, the maximum BTE achieved by using pure D100 fuel is 30.75%, indicating a significant increase of 17.07% in BTE at a specific crank angle of 23.5° before top dead centre (TDC). When subjected to maximum operational capacity, the use of a hydrogen blend comprising 5% of the overall fuel mixture with diesel fuel resulted in the smallest rise in brake thermal efficiency (BTE), measuring around 11.1%. The experimental findings indicated that the hydrogen sample exhibited reduced stiffness and density, leading to improved engine performance, which was attributed to enhanced atomization [22,23]. Additionally, the introduction of hydrogen into diesel fuel resulted in an enhancement of the mixing ratio, hence facilitating a more thorough combustion process due to its accelerated evaporation rate 19, 20. The present research demonstrates the use of hydrogen in the combustion process. This study determined that the brake thermal efficiency (BTE) values were 30.75% for diesel, 30.9% for DP20, 34.5% for DP20H5, 36.4% for DP20H10, and 37.08% for DP20H15 when measured at 23.5° b TDC at full engine load conditions.

3.2. Brake-Specific Fuel Consumption

Specific fuel consumption (SFC) is defined as the quotient obtained by dividing the mass flow rate of fuel by the engine capacity. The parameter being referred to is the fuel efficiency of an engine, which quantifies the engine’s ability to effectively utilise fuel resources. This metric is determined by evaluating the specific attributes of the fuel in question, with one value being provided as an example [24,25]. Figure 4 illustrates the performance of the SFC under different engine settings, namely, using diesel fuel (D100), as well as blends, including 5%, 10%, and 15% hydrogen (DP20H5, DP20H10, and DP20H15, respectively). Typically, the SFC exhibits a reduction with an increase in engine load. This observation suggests that the engine exhibits improved performance when subjected to higher levels of workload. The graph illustrates that the SFC of the DP20H5, DP20H10, and DP20H15 engines is consistently lower than that of the D100 engine across all test situations. According to available reports, the lowest SFC for diesel fuel with a hydrogen content of 15% is documented as 142.0 g/kWh. Conversely, the highest BSFC for D100 fuel is recorded as 275.4 g/kWh. When subjected to maximum load, the 10% hydrogen diesel fuel mix exhibited the second lowest SFC efficiency. The SFC exhibits a reduction with the introduction of hydrogen into the diesel fuel, in comparison to the SFC observed for D100 [26,27].

3.3. Exhaust Gas Temperature

Figure 5 illustrates the exhaust gas temperature (EGT) under different engine settings, namely, using diesel fuel (D100), a blend of 5% hydrogen (DP20H5), a blend of 10% hydrogen (DP20H10), and a blend of 15% hydrogen (DP20H15). Typically, the exhaust gas temperature (EGT) has a positive correlation with the engine load [28,29], wherein an increase in engine load results in a rise in EGT. This observation suggests that the engine exhibits enhanced performance when subjected to higher levels of workload. The experimental results indicate that the exhaust gas temperature (EGT) of the DP20H5, DP20H10, and DP20H15 engines is consistently greater than that of the D100 and DP20 engines, as seen in the graph. It has been observed that the lowest EGT for diesel fuel is 451 °C for diesel (D100), whereas the highest EGT for a DH15 sample is 602 °C. The hydrogen diesel fuel mix with a concentration of 15% exhibited the greatest exhaust gas temperature (EGT) at maximum load. Specifically, the EGT reached around 25.0% at 23.5 b TDC (before top dead centre) while the engine was operating at full load (10 kg load).

3.4. Cylinder Pressure

Figure 6 illustrates the cylinder pressure observed across several engine settings, namely, diesel (D100), DP20, DP20H5 (5% hydrogen), DP20H10 (10% hydrogen), and DP20H15 (15% hydrogen). According to the graphical representation, it can be seen that the cylinder pressure of the DP20H5, DP20H10, and DP20H15 engines surpasses that of the D100 engine across all test settings. The declared minimum cylinder pressure for diesel fuel is 76.7 bar; however, the DH15 sample has a maximum cylinder pressure of 90.5 bar at 23.5° b TDC. The experimental results indicate that the diesel fuel mix containing 15% hydrogen exhibited the greatest pressure while operating at maximum capacity, with a recorded value of around 15.2%. This study examines the impact of hydrogen addition on the fluctuation in cylinder pressure during combustion, in comparison to the use of D100 fuel. Noticeable alterations are seen in diesel fuel that includes 10% and 15% hydrogen. The cylinder pressure exhibits an increase at different engine settings when a hydrogen propellant is introduced [30,31]. The heating value of hydrogen is 120 MJ/k, which is 64.5% more than the heating value of diesel fuel, which is 42.5 MJ/kg.

3.5. Maximum Pressure Rise Rate

Figure 7 depicts the maximum pressure rise rate (MRPR) recorded in several engine configurations, namely, diesel (D100), DP20, DP20H5 (with 5% hydrogen), DP20H10 (with 10% hydrogen), and DP20H15 (with 15% hydrogen). Based on the graphical depiction, it is evident that the MRPR (Mean Relative Power Ratio) of the DP20H5, DP20H10, and DP20H15 engines exceeds that of the D100 engine across all tested configurations. The officially specified lowest MRPR for DP20H15 fuel is recorded as 2.87 bar per degree. However, the D100 sample has a higher MRPR value, reaching a maximum of 3.25 bar per degrees at 23.5° b TDC (before top dead centre). The experimental findings suggest that the diesel fuel blend containing 15% hydrogen had the lowest Maximum Rate of Pressure Rise (MRPR) while running at maximum capacity, with a recorded value of around 11.69%. This observation may be attributed to the cetane number of hydrogen. This research investigates the influence of hydrogen supplementation on the variability in cylinder pressure throughout the process of combustion, in contrast to the utilisation of D100 fuel. Significant modifications are seen in diesel fuel containing 10% and 15% hydrogen. The MRPR demonstrates a decline at various engine configurations with the introduction of hydrogen propellant [32,33]. The heating value of hydrogen is recorded at 120 MJ/k, representing a 64.5% increase compared to the heating value of diesel fuel, which is measured at 42.5 MJ/kg. Table 1 displays the cetane number values for hydrogen and diesel fuel, which range from 5 to 10 and 48 to 52, respectively.

3.6. Ignition Delay

Figure 8 depicts the ignition delay (ID) recorded in several engine configurations, namely, diesel (D100), DP20, DP20H5 (with 5 lpm hydrogen), DP20H10 (with 10 lpm hydrogen), and DP20H15 (with 15 lpm hydrogen). Based on the graphical depiction, it is evident that the ID of the DP20H5, DP20H10, and DP20H15 engines exceeds that of the D100 engine across all tested configurations. The officially specified minimum ID for D100 fuel is recorded as 15.6 degrees. However, the DP20H15 sample has a higher ID value, reaching a maximum of 22.9 degrees at 23.5° b TDC (before top dead centre). The experimental findings suggest that the diesel fuel blend containing 15 lpm hydrogen had the higher ID while running at maximum capacity, with a recorded value of around 31.8%. This observation may be attributed to the lower cetane number of hydrogen blends. This research investigates the influence of hydrogen supplementation on the variability in cylinder pressure throughout the process of combustion, in contrast to the utilisation of D100 fuel. Significant modifications are seen in diesel fuel containing 10 and 15 lpm hydrogen. The ID demonstrates a decline at various engine configurations with the introduction of hydrogen propellant [34,35,36]. Table 1 displays the cetane number values for hydrogen and diesel fuel, which range from 5 to 10 and 48 to 52, respectively.

3.7. Smoke Emission

Smoke is the result of the decomposition of complex hydrocarbons in a compression ignition engine. Carbon particles aggregate until they undergo oxidation in the fuel-deficient area. The rate of soot production is calculated based on the disparity between the formation rate and the oxidation rate of carbon. The exhaust smoke is evident because of the limited amount of fuel injected. To decrees smoke emissions, one can advance the injection timing or use a fine fuel spray, achieved through increased injection pressure and finer nozzles [37]. Figure 9 depicts the smoke emissions recorded in several engine configurations, namely, diesel (D100), DP20, DP20H5 (with 5 lpm hydrogen), DP20H10 (with 10 lpm hydrogen), and DP20H15 (with 15 lpm hydrogen). In a diesel engine, the creation of smoke emissions is typically governed by parameters such as high cylinder temperature, oxygen concentration in the local burning zones, residence length, the latent heat of evaporation, and engine operating state [38].

3.8. Oxides of Nitrogen Emission

Figure 10 depicts the oxides of nitrogen (NOx) emissions recorded in several engine configurations, namely, diesel (D100), DP20, DP20H5 (with 5 lpm hydrogen), DP20H10 (with 10 lpm hydrogen), and DP20H15 (with 15 lpm hydrogen). In a diesel engine, the creation of oxides of nitrogen (NOx) is typically governed by parameters such as the high cylinder temperature, the oxygen concentration in the local burning zones, the residence length, the latent heat of evaporation, and the engine operating state [37,38]. Every single gasoline sample that was examined exhibited the same trend of NOx generation with increasing engine load. The increasing temperature of the cylinder is the reason for the higher NOx emission consequences [39,40]. Figure 9 displays the NOx emissions under different diesel (D100), 20% waste-plastic oil biofuel with diesel (DP20), 5 lpm hydrogen (DP20H5), 10 lpm hydrogen (DP20H10), and 15 lpm hydrogen (DP20H15) engine settings. As demonstrated by the graph, under all test circumstances, the NOx emission of the DP20H5, DP20H10, and DP20H15 engines is greater than that of the D100. The highest NOx emissions for HP20D15 have been reported to be 51.0 g/kWh, whereas the lowest NOx emissions for D100 sample is 6.9 g/kWh. The 10 lpm hydrogen–DP20 mix produced the second highest NOx emissions at full load conditions, which was around 61.3%. This demonstrates how the addition of hydrogen influences the variance in NOx emissions during combustion compared to D100 and DP20 mixes. Significant alterations are noticed in diesel fuel containing hydrogen. At different engine settings, the NOx emissions rise with the addition of hydrogen propellant and engine load [41,42].

3.9. CO Emission

Figure 11 depicts the CO emissions recorded in several engine configurations, namely, diesel (D100), DP20, DP20H5 (with 5 lpm hydrogen), DP20H10 (with 10 lpm hydrogen), and DP20H15 (with 15 lpm hydrogen). In a diesel engine, the creation of CO emissions is typically governed by parameters such as high cylinder temperature, oxygen concentration in the local burning zones, residence length, the latent heat of evaporation, and engine operating state [39,40]. Alternative fuel blends emit less CO emissions that hydrogen blend fuels due to their superior combustion characteristics. As the fuel injection timing increases, this leads to decreases in CO emissions [41,42].

3.10. HC Emission

Hydrocarbon (HC) emissions represent the quantification of hydrocarbons that have been efficiency burned during the process of combustion. Figure 12 illustrates the comparison of HC emissions for various hydrogen flow rates provided through induction and advanced fuel injection timing. Based on the experimental findings, the hydrocarbon flow amounts exhibited lower values of HC emissions capered to diesel and biodiesel blends. Therefore, a higher concentration of hydrogen results in a decrease in the emission of HC in the exhaust. Figure 12 depicts the HC emissions recorded in several engine configurations, namely, diesel (D100), DP20, DP20H5 (with 5% hydrogen), DP20H10 (with 10% hydrogen), and DP20H15 (with 15% hydrogen). Fuel blends emit less HC emissions due to the presence of hydrogen in the blends, which is owed to superior combustion characteristics of hydrogen [41,42]. As the fuel injection timing increases, this leads to decreases in HC emissions by up to 23.5 b TDC.

4. Conclusions

The current study aimed to assess the impact of hydrogen, added at concentrations of 5%, 10%, and 15%, to diesel fuel under different engine load conditions. These conditions were represented by D100, DP20, DP20H5, DP20H10, and DP20H15. The following passage presents a concise overview of the ongoing research:

• The maximum brake thermal efficiency (BTE) observed for a DP20H15 mixture containing 15% hydrogen with 85% DP20 is 37.0%, while the lowest BTE recorded for D100 fuel is 30.75%. This indicates that the BTE has seen a 16.8% increase. The improved performance of the engine may be attributed to the reduced stiffness and density of the hydrogen sample, which facilitated the efficient fragmentation of hydrogen into smaller particles. Additionally, DP20H5 displayed a reduction in fuel consumption of 10.9% at 23.5 b° TDC at full load conditions.
• According to the available information, it has been reported that the lowest specific fuel consumption (SFC) for a mix of DP20 with 15% hydrogen is estimated to be 142.0 g/kWh. In contrast, the maximum SFC recorded for D100 fuel is reported to be 275.5 g/kWh.
• The increase in pressure inside the cylinder may be attributed to the change in temperature, which subsequently affected the quantity of hydrogen present in the mixture. At its maximum operational threshold, which reached around 6.5% for DP20H5, 17.6% for DP20H10, and 19.7% for DP20H15, the fuel mix consisting of waste-plastic oil biofuel–diesel–hydrogen exhibited the greatest pressure. This study examines the impact of the addition of hydrogen on the alteration of cylinder pressure throughout the combustion process, in comparison to the use of D100 fuel.
• The introduction of hydrogen into diesel fuel shows a potential improvement in the levels of nitrogen oxide (NOx) emissions for DP20H5, DP20H10, and DP20H15 while operating at full load settings.
• A decrease in HC and CO emissions was seen in response to the rise in cylinder temperature, concomitant with an increase in the hydrogen content within the mixture of up to 23.5° b TDC injection timing. Furthermore, it was observed that the emission of HC emissions increased proportionally with the increased advanced fuel injection timing.