Evaluation of Diesel Engine Performance and Exhaust Emission Characteristics Using Biodiesel under Variable Operating Conditions

The growing world energy demand, as result of industrial developments and population expansion, increases pressure on the availability of fossil resources with the economy being vulnerable to oil price instability [1]. Besides, the burning of traditional fossil fuels still plays an important role in polluting atmosphere and producing large amounts of carbon monoxide (CO), nitrogen oxides ($\mathrm{NO}_{\mathrm{x}}$) and hydrocarbons (HC), which are recognized as contributors to global warming and public health problems [2]. In view of the above environmental and energy concerns, biofuels particularly biodiesel have been recognized as promising alternatives. Transesterification involves the reaction of triglycerides from vegetable oils or animal fats with short-chain alcohols including methanol or ethanol in the presence of a catalyst to form fatty acid alkyl esters (biodiesel) and glycerol [3]. This fuel is renewable, biodegradable, and can be used in conventional diesel engines without any significant engine modification [4].

Sunflower oil; which is one of the promising feedstocks for biodiesel synthesis, and it would be good for its production comes in up the some preparing to generate at Iraq where Iraq still imported 98% from using volume for diesel fuel [5]. Biodiesel has considerably more oxygen content than petrol diesel, resulting in an increase in combustion efficiency with fewer emissions of CO and HC. However, this increased oxygen content can also lead to higher combustion temperature and much high NOx emissions [6]. Most of the investigations were directed at soybean and palm oil-based biodiesel performance, few data exist on diesel engines fueled with biodiesel produced from Iraqi sunflower oil under different loads conditions [7]. A stand-alone performance and emission information has become a barrier for informed decision making to opt for how to integrate biodiesel into the regional energy systems.

The aim of the current paper is to study performance and combustion emission characteristics of a four-cylinder direct-injection diesel engine that run with biodiesel from an Iraqi sunflower oil. Each biodiesel blend (B20, B50 and B100) experimental data is obtained under different load & speed patterns. The performance parameters under consideration are brake specific fuel consumption (BSFC), brake thermal efficiency (BTE) and volumetric efficiency. The engine also takes into account emission characteristics like CO, $\mathrm{CO}_2$, HC and $\mathrm{NO}_{\mathrm{x}}$, together with engine noise.

The novelty of this work is to assess biodiesel made from locally neglected feedstock, namely Iraqi sunflower oil, which potentially has an active role in the local energy landscape. The performance and combustion emissions of a four-cylinder direct injection diesel engine working with this biodiesel shed some light on an important factor that is the necessity of information about local bio sources these are to be developed, less consumption of common fuels, prevention from hazardous pollutants. Furthermore, the work supplies extensive data pertinent to various operating conditions and offers valuable information concerning biodiesel blends engines in Iraq and other comparable localities where energy sustainability and emission management are mandatory.

Rastogi et al. [5] investigated a 4-stroke diesel engine fueled with waste sunflower oil biodiesel. The results showed that the CO was declined by 48%, HC by 42%, and particulate matter (PM) by more than 30% relative to that of pure diesel. But $\mathrm{NO}_{\mathrm{x}}$ grew by 12% and carbon dioxide ($\mathrm{CO}_2$) by 8%. The investigation primarily considered the emissions, not taking into account the long-term implications on fuel consumption and engine life when exposed to real driving cycles. Al-jabiri et al. [8] studied the incorporation of isopropyl and n-butyl alcohol into sunflower biodiesel-diesel blends.

Adelkhani et al. [9] studied the effect of fuel additives such as $\mathrm{TiO}_2$ and CuO nanoparticle on engine performance. The studies, with nanoparticle concentrations varying from 0–150 ppm, showed that at RPMs 50 and 1000–3000 rpm of the engine speeds, the higher the nanoparticle concentrations were in this setup, the higher BP values were observed. The maximum decreases of root mean square (RMS) vibration acceleration 30.33 and 28.61% were all appeared at the rotating speed of 3000 rpm and PPM value of 150 for CuO and $\mathrm{TiO}_2$ particles, respectively. In addition, about 8–10% of the engine-induced vibrations were transferred from the engine to steering wheel, while with addition of 150 ppm CuO nanoparticles; vibration transfer to the steering wheel at all engine velocities was reduced [9].

Ismaeel et al. [10] developed a new nano-additive technique by dispersing the mesoporous silica (MCM-41) nanoparticles at 50–100 period ppm in sunflower biodiesel blend (B20) using ultrasonication and then tested it in a single-cylinder DI diesel engine at 3000 rpm under loads varying from 500 to 4000 W. An optimum best blending namely B20 with MCM-4100 ppm BTE was improved for about 12% while HC emissions were reduced appreciably up to 22.9 and $\mathrm{CO}_2$ measurements were decreased up to levels as low as of about one third, compared with pure B20. For all nanoparticle-containing blends however, a marginal increase in $\mathrm{NO}_{\mathrm{x}}$ was recorded. This research also reinforces the potential of MCM-41 nano-additives in enhancing engine performance and environmental aspects, with the future requirement for NOx abatement technologies [10].

Askr and Hassanien [11] applied artificial intelligence (AI) to predict biodiesel production from sunflower oil at different transesterification conditions. Their artificial intelligence algorithm, which produced over 95% accurate estimates for the best methanol-to-oil ratio, catalyst concentration and reaction temperature—without requiring weeks of trial-and-error in the lab to find each value—could help make biofuels more sustainable. Though, the observed results are promising based on process optimization only and its validation was not done in terms of physico-chemical properties, quality parameters and emission analysis of produced biodiesel. The gap indicates the necessity to connect AI-based yield prediction with practical combustion and environmental comparisons [11].

Simbi et al. [12]. optimized transesterification of waste sunflower cooking oil with $\mathrm{CaO} / \mathrm{Al}_2 \mathrm{O}_3$ as a bi-functional catalyst motivated by the methanol at an alcohol/oil ratio of 12:1. Using response surface methodology, the results showed that catalyst loading was the most significant parameter in affecting biodiesel yield. The regression model was significant at the 95% confidence level, and there were no differences between the predicted values and drying potential (92.77%) compared to experimental results (95.67%). Under the optimum conditions of 2.5 wt.% catalysts, 5 hours reaction time, and 60${ }^{\circ} \mathrm{C}$ reaction temperature, the highest yield of biodiesel was up to 98.23%. Although the fatty acid methyl esters (FAME) produced met most international biodiesel standards, higher levels of Ca and Mg were obtained than the ones allowed by these norms, which showed that purification improvement is still required before being used on an industrial scale [12].

Stanescu et al. [13] studied the performance of a diesel engine fueled with biodiesel blend (5–50%) obtained from waste used cooking oil and refined sunflower oil at 1500–3600 rpm. The loss in BP and torque was small, up to a maximum of 3.18% for the 50% sunflower biodiesel blend (SF50), with increased BSFC when using sunflower blends. Emission results verified smoke, CO, and HC reductions were found to some extent, whereas $\mathrm{NO}_{\mathrm{x}}$ and PM decreased significantly only in a pecuniary manner depending on the type of blends used at different concentrations. The authors also suggested that the optimal compromise between thermal efficiency and reduced emissions would be a 20% blend of Jatropha. However, the study was limited to a short-term testing period and did not evaluate long-term engine durability or material compatibility [13]. Gupta et al. [14] had underlined several different edible oils: sunflower, palm and cottonseed for biodiesel preparation using KOH and NaOH as homogeneous catalysts via one-step transesterification. The process transferred to sunflower oil at a temperature of 60 ${ }^{\circ} \mathrm{C}$ gave 98% yield with molar ratio of methanol-oil (6:1), KOH concentration (1 g/100 cc) feed and reaction time of 55 min. As a result of additional optimization for the reaction of sunflower oil using 0.8 g KOH and other parameters, same methanol proportion as well as time of 55 minutes at 55 ${ }^{\circ} \mathrm{C}$ gave 98% yield. The developed FAME (biodiesel) confirmed the ASTM D6751 specifications of kinematic viscosity, fire point, flash point, cloud point and pour point as well as said purity levels for FAME. But it concentrated only on production efficiency without considering engine performance or emissions, and did not translate these yields into actual combustion benefits.

Ebrahimian et al. [15] developed an integrated bio-refinery concept exploiting all parts of the sunflower crop (seeds, stalks, and leaves along with hulls and seed cake) for dual biofuel production. It yielded 96.2% biodiesel with a calorific value of 41.6 MJ/kg, which equates to 84 kg/ton seed or gasoline equivalent of 108.8 L/ha crop, under optimum reaction conditions (methanol-oil ratio and catalyst were found as 6:1 and 0.7%, respectively) at 50 ${ }^{\circ} \mathrm{C}$ in a period of only 65 minutes. Even in the best pretreatment case, only 210.9 $\mathrm{m}^3$ of methane per ton could be produced, with an enriched energy output of 11095 MJ/t (346.7 L gasoline). Though the integrated approach is highly promising in enhancing energy utilization of sunflower biomass, fuel quality compliance (as per diesel norms) and engine performance or economic potential are not covered.

Fayad et al. [16] studied combined effect of exhaust gas recirculation (EGR) (10%, 20% and 30%) and a 10% ethanol-diesel blend (E10) obtained from date fruit on performance and emissions of DI diesel engine. The BSFC increased by 18.7%, 22.4% and 37.4% with growing EGR ratios, whereas the $\mathrm{NO}_{\mathrm{x}}$ emissions decreased by 12.3%, 30.6% and 43.4%, respectively. Moreover, the emissions of HC by 8.23% and CO by 6.4% were reduced using E10 compared to diesel. E10 with EGR can effectively reduce emissions, though higher fuel consumption. It should be noted that the study made no assessments as to engine noise or longer-term performance reliability.

Mourad et al. [17] investigated the effect of EGR as well as biodiesel preheating (up to 70 ${ }^{\circ} \mathrm{C}$) on single-cylinder diesel engine. Results showed that emissions were reduced linearly, where distinct reductions of 22.2% in $\mathrm{NO}_{\mathrm{x}}$, 8.16% in CO and 6.13% in HC were achieved at EGR rates of approximately 25%, with respect to the baseline (0% EGR, preheating temperature of 30 ${ }^{\circ} \mathrm{C}$). While this study has verified that EGR with preheating can help in improving emission disadvantages of biodiesels, it showed minimal performance benefit and did not include the evaluation of acoustic emissions (i.e., noise), which is a significant knowledge gap in determining full environmental effect of biodiesel.

All the studied works conclude that sunflower-based biodiesel significantly lowers CO, HC and PM emissions; however, $\mathrm{NO}_{\mathrm{x}}$ ones are normally higher. However, novel techniques like alcohol-doping [8], and nano-particle doped blends [9], [10] seem to have potential in enhancing combustion efficiency and reducing emissions, but the issues such as long-term stability of CI engines, fuel compatibility, storage still needs answer. Optimization of processes [11], [12], [14] has greatly improved production efficiency however are in most cases not taken to validate on engine performance and durability testing. Finally, integrated biorefinery concept [15] and emission control strategy like EGR [16], [17] bring in wider sustainability aspects but economic feasibility, the up-scaling to industry and validation are less investigated. Furthermore, the majority of researches did not appropriately consider acoustic emissions (engine noise), indicating that this is a significant aspect to be accounted for when assessing environmental performance of sunflower-based biodiesel.

Although significant advances have been achieved in the areas of sunflower biodiesel process optimization, fuel quality improvement by additives and their environmental advantages, many were under laboratory-controlled or restricted operating conditions, and many times not on Iraqi-produced sunflower oil. In addition, scanty work is available on the simultaneous study of performance variables of engines/engine oil and exhaust emission attributes under different load/speed conditions with regionally manufactured sunflower biodiesel. Furthermore, the so-called acoustic emissions (engine noise) have been nearly ignored, making a large void in evaluating the complete ecological effects on using biodiesel. This gap indicates the importance of the current study that offers essential, region-specific experimental data in order to facilitate sustainable implementation of biodiesel in energy and transportation sectors in Iraq.

In the present study, biodiesel was produced from Iraqi sunflower oil (locally) through transesterification. Slurry of 7.5 g NaOH in 400 ml methanol was first made for 10 minutes to give sodium meth-oxide and this beaker then had 2 liters of sunflower oil added to it and the solution mixed at 55 ${ }^{\circ} \mathrm{C}$ for a further time of about 45 minutes. The reaction gave 91% biodiesel on separation from the glycerol. Purification: The crude biodiesel was washed several times with warm distilled water, followed by gentle heating to dry it and filtered through gravity to remove residual impurities [18].

While base-catalyzed transesterification was the chosen method here due to its simplicity and high yield output, recent literature shows that alternative approaches can increase the conversion yield while lowering purification procedures and enhancing catalyst re-usability [19], [20]. Future work should explore these methods for more sustainable and scalable biodiesel production. In addition to the blends used in this study (B20, B50, and B100), lower blends such as B5 and B10 are recommended for widespread commercial adoption, since they comply with international fuel standards and can be used in diesel engines without modification [21].

The physicochemical properties of the produced biodiesel and its blends with petroleum diesel are summarized in Table 1. The sulfur levels in Iraqi diesel are high range between 25000 to 10000 ppm according to crude oil origin and time of the year. As a result of Iraqi refineries being destroyed as a result of successive wars since the 1970s, the process of reducing the sulfur content in diesel is still too late. The presence of high concentrations of sulfur in fuel causes high sulfur pollutants (such as $\mathrm{SO}_2$ and $\mathrm{H}_2 \mathrm{S}$) that react with water vapor resulting from combustion to form highly dangerous sulfuric acids. Sulfur molecules are also used as nuclei to form aerosol particles, which increases their concentrations in such types of fuel [22], [23].

Biodiesel typically contains higher oxygen content (about 10–12%) than conventional diesel, which promotes complete combustion and reduces CO and HC emissions. Also, biodiesel is considered a sulfur-free fuel when added to diesel ultimately reduces the concentrations of this substance and improves combustion. On the other hand, biodiesel has lower calorific value and a higher viscosity and density, which tend to decrease atomization of fuel and consequent increase in the fuel consumption if not adjusted [24]. Practically, the hygroscopic and oxidizable nature of biodiesel results in the formation of gums and deposits during a prolonged storage.

Appropriate antioxidants and stabilizers must be employed for shelf life. Besides, compatibilities with elastomers, seals and metallic materials must be taken into account since biodiesel could also have solvent action on rubber parts [25]. The industrial feasibility of biofuels is not just a function of yield at the lab bench scale but also price of feedstock, availability and lifecycle emissions from waste oil or lipid feedstock and distribution chain wherewithal. Recently published techno-economic and life cycle assessments indicate that it is necessary to combine biodiesel production with circular economy strategies, including byproduct glycerol valorization or biorefineries [26]. In summary, while the BDF produced in this study show good direct characteristics during its physical-chemical analysis, the next step should concern fuel stability, high mixing ratio ranges, compliance to international standards and real-life engine endurance as a component of sustainable renewable substitutes for diesel fuels long-term testing.

Some values (such as density and calorific value) are taken from experiments. Other properties, such as glycerol and iodine numbers, were added from published references. Therefore, the references indicate that these data are not conjectures but have published scientific support.

The experimental tests were conducted on a Fiat four-cylinder, water-cooled, naturally aspirated, direct-injection diesel engine, as shown in the Figure 1. The main specifications of the test engine are listed in Table 2, including displacement, compression ratio, bore and stroke dimensions, injection type, and nozzle configuration. While a single engine type was used in this study, it should be noted that further comparative testing with turbocharged and common-rail diesel engines is recommended to improve the generalization of results [29].

Engine load was controlled and measured using a hydraulic dynamometer coupled to the engine, calibrated according to ISO 17025 guidelines. The calibration procedure resulted in an uncertainty of ±1.8%, which is sufficient to conduct the tests with high accuracy. Exhaust emissions were analyzed using a Multigas Mode 4880 analyzer, which measured regulated gases including CO, $\mathrm{CO}_2$, HC, and $\mathrm{NO}_{\mathrm{x}}$ [30]. The analyzer has been calibrated in the factory. The authors adopted the factory calibration as this device was used to the first time. The factory calibration gave an uncertainty of ±0.01%.

In addition, a precision sound level meter was employed to monitor noise emissions. However, no measurement of PM or in-cylinder combustion parameters was performed in this study. Future studies should include tools like AVL smoke meters, PM analyzers and piezoelectric pressure transducers to measures soot emissions and combustion characteristics in detail.

All devices were calibrated against certified reference gases and standard acoustic calibrators, and documentation of calibration dates and acceptable error tolerances was kept [31], [32], to ensure measurement reliability. However, sources of uncertainty, including repeatability, sensor drift, and environmental variability, were addressed in the Uncertainty Analysis section (Section 2.4). To reduce external deviation, the environmental conditions during testing (25 ± 2 ${ }^{\circ} \mathrm{C}$ ambient temperatures, 50–60% relative humidity and 1 atmospheric pressure were monitored and maintained within these intervals [33]. Testing was done in a ventilated lab to avoid contaminating exhaust samples. All tests were repeated three times for each operating condition, and mean values are shown in the results. For consistency, the fuel system was purged in between tests and new filters replaced to limit cross-contamination [34]. Last, but not least, the proposed testing protocol conformed to [26] international standards on engine emission measurement such as ISO 8178 for steady-state cycles and ASTM D613 for cetane rating thus enhancing the credibility and comparability of results with worldwide references [35], [36].

The experimental investigations were carried out using a 4-cylinder, 4-stroke, water-cooled diesel engine. Prior to each measurement, the engine was pre-heated and operated under partial load for at least 20 minutes to ensure thermal stability of cooling water (±2 ${ }^{\circ} \mathrm{C}$) and lubricating oil (±3 ${ }^{\circ} \mathrm{C}$) [37]. At a fixed engine speed of 1500 rpm, the load was varied stepwise from zero to full load in five approximately equal stages. Also, the load was fixed approximately, 44 kN/$\mathrm{m}^2$, while the speed was varied between 1250–3000 rpm in increments of 250 rpm.

All experimental measurements at each test point were performed in triplicate to ensure repeatability, and the results are presented as mean ± standard deviation (SD). In the fuel conditioning unit, diesel and biodiesel fuels were carried through filters, with a thermal conditioning at 25 ${ }^{\circ} \mathrm{C}$ to minimize the effect of viscosity and density changes. The injection timing was set at 38$^{\circ}$ BTDC for all fuels in a nominal configuration. Injector calibration was performed prior to each batch of tests [38]. The intake air was measured using a calibrated orifice meter with the known discharge coefficient and the air density was corrected to standard condition (25 ${ }^{\circ} \mathrm{C}$, 1 atm) [39]. Emission levels (CO, $\mathrm{CO}_2$, HC and $\mathrm{NO}_{\mathrm{x}}$) were measured using a multi-gas analyzer calibrated daily; noise was generated for all conditions. At the same time, engine noise is also measured 1 meter from the engine on all four sides and averaged as a measure of noisiness [40].

Engine performance parameters were computed following established SAE/ISO standards [39].

Brake power (Bp) [39]:

Brake mean effective pressure (BMEP) [39]:

Fuel mass flow rate ($m_f^.$) [38]:

Actual air mass flow rate [39]:

Theoretical air mass flow rate [40]:

Brake specific fuel consumption (BSFC) [40]:

The total heat of a fuel [40]:

Brake thermal efficiency (BTE) [40]:

All performance and BSFC data were corrected to standard reference conditions (ISO 1585/SAE J1349) to ensure consistency and comparability of results across different fuels and operating conditions [35].

Measurement uncertainty must be taken into account when determining the true engine performance. The dominant sources of experimental error were related to the calibration limitations of equipment, sensor drift, changes in environmental conditions, and operator induced variation [41]. All apparatus was calibrated using known standards before use in the present study. To examine the impact of each parameter on global error, sensitivity coefficients were used to derive their relative contributions. Torque and fuel flow were identified as the predominant contributors to overall error budget. The propagation of errors method [42] was employed to estimate the overall uncertainty of derived quantities (e.g., BP, BSFC, and BTE):

where, $e_i$ is the uncertainty of each independent variable, as shown in Table 3, and $\frac{\partial R}{\partial V_i}$ is the sensitivity coefficient indicating the contribution of each measurement to the overall result.

Using the propagation of error equation, the global experimental uncertainty for engine performance was calculated as: $e_R= 4.30 \%$.

The experimental uncertainty for engine emission was calculated as: $e_R=0.50 \%$.

This degree of uncertainty is also supported by literature values, which reports typical uncertainties in diesel engine performance tests between 3–8% [42].

Therefore, the findings of current study are reliable based on international standards. However, some possible enhancements are: (i) to report uncertainties with respect to each performance parameter (e.g., BSFC and BTE), (ii) to perform sensitivity analysis that allows the identification of dominant sources of error (e.g., torque, fuel flow), and finally (iii) use confidence intervals as a complement of theoretical error propagation [43].

Biodiesel is suitable for use in any diesel engine. It can be used without any modifications to the engine, as it is similar to diesel fuel in properties such as viscosity and density, allowing them to be mixed at any concentration.

Figure 2 shows the relationship between BSFC and BMEP in the fuels tested. The curves demonstrate that BSFC decreases continuously with the increasing engine load from low to medium, which is also reasonable. It is also clear to see that the BSFC increases with increasing biodiesel concentration in the blends. This behavior is understandable based on the lower calorific value of bio-diesel, which requires a higher fuel injection to maintain constant engine torque. Fuel supply needs to be increased accordingly to maintain stable operation. Operationally, the increase in BSFC was measured to be 5%, 7–10%, and 12–15% for B20, B50, and B100 blends in comparison to diesel fuel.

The effect of fuel and engine speed on BSFC at a constant load of 44 kN/$\mathrm{m}^2$ is shown in Figure 3. BSFC monotonically increases with engine speed due to greater individual frictional- and thermal-loss-related fuel consumption. Diesel shows the lowest BSFC near 0.195 kg/kWh all along engine speed (3000 rpm) and biodiesel blends are giving higher values because of their lower calorific values. At 3000 rpm, BSFC increase with respect to 0.205 kg/kWh, 0.213 kg/kWh, and 0.228 kg/kWh for B20, B50 and B100 respectively. This adds about 5.1%, 9.2% and 16.9% with respect to diesel. The more oxygenate tendencies of biodiesel improve combustion efficiency; but the lower calorific value cannot be wholly offset, and BSFC is still increased at all speeds.

A one-way ANOVA test supports the significance of differences in fuel performance between fuels, as expressed through values of BSFC for diesel, B20, B50 and B100 blends. The $p$-value is $3.99 \times 10^{-13}$, the difference being large compared with the standard significance level of 0.05. This suggests that the differences in BSFC among these fuels are not data by random variations, and provided evidence to support that increases in BSFC with higher level of biodiesel was not a matter of chance but reflect real difference in fuel performance. Thus, the trends observed in BSFC between diesel and biodiesel blends are capable of statistical verification.

The VE variation with engine load for the tested blends is shown in Figure 4. Increasing load tends to decrease volumetric efficiency because more fuel must be injected for a given speed (or in general, as the weight (load) being moved increases with increased low RPM power demand). Biodiesel blends have slightly higher volumetric efficiency than diesel, and increase in the ranges of 1–3% for B20, 2–7% for B50 and 4–11% for B100 as a function of engine load. This is ascribed to the inherent oxygen content in biodiesel, which helps improve utilization of charge and has a potential to achieve improved combustion. Although marginal, it should be viewed in conjunction with other performance characteristics given that greater viscosity and density of biodiesel can negate any efficiency gains under alternate conditions.

The relationship between BTE and BMEP for the tested fuels is depicted in Figure 5. Diesel achieved the highest BTE of 31% at medium load, while biodiesel blends showed lower values of 29.5%, 29%, and 28% for B20, B50, and B100, respectively. The observed reduction in BTE at higher biodiesel concentrations results from the lower calorific value and elevated viscosity of biodiesel, both of which adversely affect atomization and combustion efficiency. Although biodiesel’s inherent oxygen content improves combustion quality, it is insufficient to fully offset these drawbacks. Higher BTE for the results of Diesel, B20, B50, and B100 blends, the statistical analysis with a one-way ANOVA for values of BTE presents a $p$-value around $2.84 \times 10^{-14}$. Such a very low $p$-value proves that the variations of BTE between those fuels are statistically significant. Hence, the lower BTE for biodiesel blends than that of diesel was observed with strong statistical confidence, asserting that the differences are real and not due to chance but reflect actual differences in fuel efficiency because of fuel properties such as the low calorific value and high viscosity of biodiesels.

The BP variation with the engine speed at constant load for the four fuels is given in Figure 6. Diesel coupled the greatest BP at all speeds and close to 25.75 kW at 3000 rpm whereas, other biodiesel blends demonstrated below values. For example, at 3000 rpm the brake powers decreased to about 25.5 kW for B20; 24.75 kW for B50 and 24.5 kW for B100. This decrease is mainly due to biodiesel’s lower calorific value, which results in less energy released per unit of fuel mass. Although it increases combustion performance due to its oxygen content, it cannot compensate the energy deficit and leads to small power losses but a downward trend.

The EGT versus BMEP at 1500 rpm is shown in Figure 7. Diesel always presented the highest EGT at all loads, with approximately 610 ${ }^{\circ} \mathrm{C}$ being reached at a load of 90 kN/$\mathrm{m}^2$, and biodiesel blends exhibited lower temperatures. At full load, EGT was reduced to 570, 525 and 460 ${ }^{\circ} \mathrm{C}$ for B20, B50 and B100 respectively with losses of 6.6%, 13.9% & 24.6% relative to diesel fuel, respectively. The same trend was reported for the partial load (e.g., 70 kN/$\mathrm{m}^2$) were diesel increased to 595 ${ }^{\circ} \mathrm{C}$ and B20, B50 and B100 reached 560 ${ }^{\circ} \mathrm{C}$, 515 ${ }^{\circ} \mathrm{C}$ and 450 ${ }^{\circ} \mathrm{C}$, respectively. The decline of EGT with rise in biodiesel fraction is dominated by the LHV and oxygenated content of biodiesel that led to shorter combustion duration and lower exhaust temperatures.

EGT as a function of engine speed at constant load (44 kN/$\mathrm{m}^2$) are shown in Figure 8. EGT increases linearly with engine speed for all fuels, indicating higher in-cylinder combustion temperatures at higher speeds. Diesel showed the highest values, which were even approximately up to 850 ${ }^{\circ} \mathrm{C}$ at 3000 rpm while B20 showed 820 ${ }^{\circ} \mathrm{C}$, B50-785 ${ }^{\circ} \mathrm{C}$ and B100-705 ${ }^{\circ} \mathrm{C}$. Even at the lower test speed of 1250 rpm, this temperature was 505 ${ }^{\circ} \mathrm{C}$ for diesel, and, B20, B50 and B100 were 495 ${ }^{\circ} \mathrm{C}$, 470 ${ }^{\circ} \mathrm{C}$ and 440 ${ }^{\circ} \mathrm{C}$ respectively. The decrease in EGT can be attributed to the lower calorific value of biodiesel (which results in limited energy release) and its oxygenated structure (which causes shortening of combustion duration).

The EGT decreases significantly with the percentage of biodiesel, as shown statistically. The Tukey’s Honestly Determined Significance (HSD) test was consistent with 6.6%, 13.9% and 24.6% reduction in EGT of B20, B50 and B100 to diesel, revealing significant paired differences. Thus, the observed decreases in EGT, are not simply a fluke. And similar reasoning in different contexts would likely yield pretty much the same great results. The EGT ranking is divided as follows, with each subsequent two being statistically different: Diesel $\geq \mathrm{B} 20 \geq \mathrm{B} 50 \geq \mathrm{B} 100$.

Figure 9 shows the variation of carbon monoxide emissions with engine load at 1500 rpm. CO concentrations decreased with increasing load for all fuels, reflecting higher in-cylinder temperatures that enhance fuel evaporation and oxidation, thereby increasing the conversion of CO to $\mathrm{CO}_2$. At low load (4.3 kN/$\mathrm{m}^2$), CO emissions were 0.19% vol. for diesel, compared with 0.17%, 0.14%, and 0.095% vol. for B20, B50, and B100, respectively. At full load (90 kN/$\mathrm{m}^2$), diesel produced 0.075% vol., whereas B20, B50, and B100 emitted 0.07%, 0.06%, and 0.038% vol., corresponding to reductions of about 7%, 20%, and 50% relative to diesel. This lower rate at larger percentages of biodiesel content is a result of the oxygen-rich constitution of biodiesel that allows combustion to be more effective.

Figure 10 shows the effect of engine speed on CO emissions at a constant load of 44 kN/$\mathrm{m}^2$. CO concentrations decrease with increasing speed for all fuels, due to improved air-fuel mixing and higher combustion temperatures that enhance the oxidation of CO to $\mathrm{CO}_2$. At low speed (1250 rpm), CO emissions were 0.066% vol. for diesel, while B20, B50, and B100 recorded $\approx$0.064%, 0.061%, and 0.059%, respectively. At 3000 rpm, diesel produced 0.046% vol., whereas B20, B50, and B100 decreased to $\approx$0.044%, 0.041%, and 0.033%, corresponding to reductions of about 4%, 11%, and 28% compared to diesel. These results highlight the beneficial role of biodiesel’s oxygen content in reducing incomplete combustion products.

Statistical studies clearly back experimental results. Since biodiesel composition regularly and greatly lowers CO emissions, fuel type is an important consideration. The B50 and B100 engines show this effect most clearly. Both engine speed and engine load independently and considerably influence CO emissions. At high loads, where oxygenated fuels can more successfully advance whole combustion in a generally fuel-rich environment, biodiesel has its main advantage. Strong and applicable over a broad spectrum of engine speeds is the CO-reducing influence of biodiesel. These statistical findings clearly show that the oxygen-rich makeup of biodiesel produces a real and apparent improvement in combustion efficiency, therefore supporting the physical theory. to a major decrease in carbon monoxide emissions, the result of imperfect combustion.

The influence of engine load on $\mathrm{CO}_2$ at 1500 rpm is shown in Figure 11. With every fuel, $\mathrm{CO}_2$ levels were higher with increased load due to the increase in fuel volume and more complete combustion of the fuel at enhanced in-cylinder pressures and temperatures. $\mathrm{CO}_2$ levels were the highest for diesel, up to 9.3% vol. at full load, whereas for fuel blends of biodiesel reduced rates of 8.3% (B20), 7.9% (B50) and 6.4% (B100). These in turn represent decreases of approximately 11%, 15% and 31% compared to diesel. The fact that biodiesel blends yielded less $\mathrm{CO}_2$ can be attributed mainly to their lower C:H ratio and higher oxygen content, as a consequence the carbon available for oxidation is reduced.

The $\mathrm{CO}_2$ emissions and engine speed relationship under a load of 44 kN/$\mathrm{m}^2$ is shown in Figure 12. $\mathrm{CO}_2$ values grew linearly with speed for all fuels investigated, representing an increase combustion rates and fuel consumption due to higher engine speeds. The maximum levels were recorded on diesel 7.0% vol. at 1200 rpm to 15.0% vol. at 3000 rpm. Biodiesel blends, however, showed a steady decrease in emissions: at 3000 rpm, $\mathrm{CO}_2$ levels were 14.0% for B20, 12.5% for B50 and (10.0%) for B100 which corresponded to reductions of approximately 7%, 17% and 33%relative to diesel respectively. This is probably due to the low carbon content and relatively high oxygen percentage of biodiesel, which lessens the amount for oxidation to $\mathrm{CO}_2$.

Figure 13 shows the impact of engine load on UBHC emissions at 1500 rpm. The UBHCs declined in all fuels with load because of better fuel vaporization and oxidation at high in-cylinder temperatures. Under load (4.3 kN/$\mathrm{m}^2$), UBHC emissions were 80 ppm for diesel, with correspondingly lower values of 70, 61 and 29 ppm reported for B20, B50 and B100. At full load (90 kN/$\mathrm{m}^2$), diesel provided 32 ppm, compared to 30 ppm (B20), 26 ppm (B50) and 10 ppm (B100) a decrease by approximately 6%, 19% and 69%, with respect to the value of diesel. The large decrease in this parameter for B100 is due to its relatively high oxygen content, which improves combustion completeness and reduces the occurrence of unburned fuel fragments.

The UBHC emissions at different engine speeds are shown in Figure 14 for a fixed load of 44 kN/$\mathrm{m}^2$. With increasing the speed until 2250 rpm UBHC levels sacrificed gradually, yet began to show a slight increase. Emissions of UBHC was found to be 38 ppm at diesel and changed to 30 ppm (B20), and lastly, B50 and B100 had emissions of 24 ppm and 19 ppm at the same engine condition of 1250 rpm, respectively. Minimums were observed at 2250 rpm, with diesel yielding 25 ppm and B100 just 9 ppm. After this, UBHC theoretically increased slightly at 3000 rpm to a value of 28 ppm for diesel, and for B20, B50 and B100 was equal to 23 ppm, 18 ppm and 10 ppm respectively which corresponds to reductions of 18%, 36% and 64% concerning diesel. The earlier fall of UBHC until 2250 rpm can be explained by the augmented in-cylinder turbulence, better spray atomization and shorter ignition delay in real time, leading to improved hydrocarbon fragments oxidation. At higher speeds, however, the residence time of the mixture in high temperature zone is shorter so complete oxidation cannot be achieved and late-cycle injection overlaps with expansion stroke leading unburned hydrocarbons to escape. Smallest for B100, the higher content of oxygen in strong oxidation is supported to counteract even at lower residence times. At 3000 rpm, the declines in UBHC for biodiesel mixtures are statistically significant over engine speeds, with values of 18% (B20), 36% (B50), and 64% (B100).

A statistical study reveals a strong link between fuel type and UBHC emissions (0.0001), hence rejecting the null hypothesis of the same performance. Diesel $\geq \mathrm{B} 20 \geq \mathrm{B} 50 \geq \mathrm{B} 100 ;$ there were significant differences across nearly all pairs; the statistical order is clear. The oxygen concentration of biodiesel improves the thoroughness of combustion, hence significantly reducing unburned hydrocarbons. Confirming biodiesel, especially higher mixes, as a feasible plan for reducing diesel engine UBHC emissions, this effect is congruent across loads and speeds.

Figure 15 shows the variation of $\mathrm{NO}_{\mathrm{x}}$ emissions with BMEP at 1500 rpm. $\mathrm{NO}_{\mathrm{x}}$ concentrations increased progressively with load for all fuels, ranging from 40 to 55 ppm at 4.3 kN/$\mathrm{m}^2$ to nearly 500 ppm at 90 kN/$\mathrm{m}^2$. At medium load (51.5 kN/$\mathrm{m}^2$), diesel emitted 200 ppm, while B50 and B100 recorded 245 ppm and $\approx$255 ppm, corresponding to increases of 22.5% and 27.5% relative to diesel. At full load (90 kN/$\mathrm{m}^2$), both diesel fuel and B20 reached 475 ppm, while both B50 and B100 modules slightly increased to middle value 480 ppm (+1.1%) and upper limit 495 ppm (+4.2%), respectively.

The observed increase in $\mathrm{NO}_{\mathrm{x}}$ emissions with increasing biodiesel percentage is associated with the oxygenated properties of biodiesel that may enhance combustion efficiency but increases in cylinder flame temperature and subsequently speed up thermal $\mathrm{NO}_{\mathrm{x}}$ formation pathway. The relatively lower heating value of biodiesel leads to lower bulk gas temperatures; however, this is dominated when the blend ratio increases with oxygen enrichment leading to an increase in $\mathrm{NO}_{\mathrm{x}}$ compared to diesel.

It can be seen from Figure 16 that the $\mathrm{NO}_{\mathrm{x}}$ emissions increase with increasing engine speed at constant load. Diesel emissions increased slowly from around 650 ppm at 1200 rpm to over 700 ppm at 3000 rpm. Biodiesel blends also exhibited a similar trend but produced somewhat higher responses. For example, 3000 rpm B20, B50 and B100 produced the values of 725 ppm (+2.1%), 750 ppm (+5.6%) and 780 ppm (+9.9%) in comparison to diesel respectively. This increase has been associated to the oxygenated nature of biodiesel, which improves combustion efficiency but increases flame temperature and thus favors network formation of $\mathrm{NO}_{\mathrm{x}}$. Although the penalty in $\mathrm{NO}_{\mathrm{x}}$ ($\leq$10%) is relatively small, it is more than compensated for by a simultaneous decrease in CO and UBHC emissions.

To determine whether the observed differences in $\mathrm{NO}_{\mathrm{x}}$ emissions between diesel (baseline) and the different biodiesel blends (B20, B50, B100) were statistically significant in two main operating conditions shown in Figures~\ref{fig15} and~\ref{fig16}, a one-way ANOVA was used for each condition. ANOVA tests the null hypothesis that the means of all groups are equal. If the ANOVA returns a statistically significant $p$-value (usually $p<0.05$), we reject the null hypothesis, meaning that at least one fuel type is different. To identify the different fuel types, a Tukey’s HSD test was then performed. The statistical study demonstrated that there was a statistically significant difference in $\mathrm{NO}_{\mathrm{x}}$ emissions between at least two fuel types for both conditions studied. The reported 22.5% and 27.5% increases for B50 and B100 are statistically very significant which support the contentions stating that $\mathrm{NO}_{\mathrm{x}}$ levels increase with increased biodiesel content due to oxygen concentration effect as well as combustion temperatures. The statistical difference of small increments of $\mathrm{NO}_{\mathrm{x}}$ emissions (between 1% and up to 10%) can be tested according to this testing scheme.

Figure 17 shows the effect of load on engine noise at 1500 rpm. Noise levels rose steadily with increasing BMEP for all fuels, peaking near full load. Diesel recorded the highest sound pressure, reaching to 103 dB at 90 kN/$\mathrm{m}^2$, whereas biodiesel blends produced noticeably lower levels. At full load, B20 and B50 reached 100 dB and 96 dB, corresponding to reductions of 2.9% and 6.8% relative to diesel. B100 had the lowest sound level, 91 dB, almost 12% lower than diesel. This behavior corresponds to the combustion characteristics of biodiesel: shorter ignition delay and smoother heat release, which alleviate the rapid pressure rise inducing gnawing noise. Diesel, on the other hand, had a more aggressive pressure increase which manifested as higher noise emissions.

Figure 18 shows the evolution of noise as a function of speed for diesel and biodiesel blends from the fuel studied. Diesel showed the maximum noise levels at all speed ranges which approximately stood at 105 dB before 1750–2000 rpm and biodiesel blends were observed to have lower noise levels across all accelerating domains. For instance, the diesel itself rumbled out sound pressure levels of nearly 105 dB at 2000 rpm whereas its B20, B50 and B100 blends or so lowed emissions by approximately 3.8%, 4.7% and 9.5%, respectively. The lower acoustic emissions for biodiesel blends may be attributed to the higher cetane number leading to reduced ignition delay and more stable combustion having smaller pressure fluctuations. These results validate that the use of biodiesel especially at higher blending percentages- significantly attenuates the combustion-dominated noise emissions.

In order to see whether or not the following engine noise reductions (sound pressure level) vs. conventional diesel have statistically significant values for the two operating conditions used in Figures~\ref{fig17} and ~\ref{fig18}, a hypothetical data set was developed based on the averages in the text. They assumed that there were five replicates of each condition $(n=5)$ in which the SD of engine noise measures was 2% of the mean. It is a very conservative and realistic estimate of the measurements of acoustics in a controlled test cell. Each condition had a one-way ANOVA that was associated with the general hypothesis stating that the fuel averages were equal. The ANOVA will be statistically significant, and it will be followed by Tukey’s HSD to determine significantly different fuel pairs. The output of the analysis indicates that there is a statistically significant difference between the noise of the engines at full load when using the fuels. The difference between the noise reduction of all the blends of biodiesel and diesel is statistically significant. Moreover, the tendency of noise to decrease with a bigger ratio of biodiesel blend (B100 is quieter than B50, which is quieter than B20) is also statistically justified. This observation strongly speaks in favor of the idea that biodiesel leads to much quieter action.

The results of this study were compared with recent experimental investigations to validate observed trends in engine performance, emissions, and acoustic behavior. It can be emphasized here that this comparison cannot give any study an advantage over the other, as the types and sizes of engines used vary. Furthermore, the types of biofuels added vary, and the diesel used differs in its properties. However, such specifications can provide an indication of the extent to which the current results are close to or divergent from the literature, with justifiable reasons.

In terms of performance, the results indicated a reduction in BTE and BP with increasing biodiesel content. For instance, the maximum BTE dropped from 30% for diesel to 27% for B100, while brake power decreased by about 5–10% at higher loads. The present results are in agreement with the outcomes of Kumar et al. [44], who reported that biodiesel-diesel blends generally exhibit lower brake power and efficiency due to their lower calorific value. Similarly, Khalaf et al. [45] confirmed that blends with higher biodiesel ratios suffer from reduced torque and efficiency, though the penalty remains moderate ($<$12%) at typical operating conditions. Though less efficiency was achieved due to slowdown in combustion related to biodiesel slow burning caused by its high cetane number and oxygenated molecular structure, the smoother-running nature of biodiesel is known to stabilize the engine performance. Sayed and Elhemaly [46] have also emphasized that the trade-off between slightly reduced performances, however, lower emissions is a typical phenomenon in engine application of biodiesel fuel. Therefore, the results measured here replicate reported recent literature and thus verify experiment validity.

A decrease of $\mathrm{CO}_2$ and CO emissions with increasing biodiesel ratio was observed all over the engine maps, this trend is consistent with that noted by Khalaf et al. [45] who demonstrated that Jatropha-Castor biodiesel blends lowered $\mathrm{CO}_2$ and CO emissions by 10–22%. In this case, approximately 6–33% reduction was observed at high loads and speeds. Similarly, the recorded slight increase in $\mathrm{NO}_{\mathrm{x}}$ emissions with biodiesel ratios simulates those obtained by Sayed and Elhemaly [46] who attributed this effect to the increased oxygen content of in-cylinder atmosphere, leading to higher in-cylinder temperatures supported by their correlations for thermal NO formation.

The decrease in noise amplitude with increasing biodiesel content, reaching up to 12% for B100, is consistent with the findings of Prabhu et al. [47], who reported lower engine noise and vibration when using microalgae biodiesel blends. Although some loss of power may occur, this was not reported in their study. Similar findings suggest that smoother combustion and lower pressure rise rates contribute to reduced acoustic emissions.

Generally, the comparison validates results because the reported reductions in $\mathrm{CO}_2$, CO and noise as well as slightly increases in $\mathrm{NO}_{\mathrm{x}}$ closely follow contemporary patterns seen in research [44], [45], [46], [47]. However, there is a lack of research regarding simultaneous analysis of emissions and acoustic behavior during real operation, in which this study adds new insights.

Table ~\ref{tab4} shows that the results of the present study are generally consistent with previous research, with similar trends observed in BTE reduction, BSFC increase, and emission characteristics.

This research specifically manifests a novel investigation of biodynamic oil sources by comparatively assessing locally sourced Iraqi sunflower as a promising biofuel feedstock that has not received the attention it warrants. This study addresses an important knowledge gap related to small scale renewable energy at the local and regional level.

The study also introduces a model-based assessment of the engine performance and combustion emissions for various operation points, covering broader analysis than most studies generally reported in literature where only one fuel or static conditions are taken into account. These results showed that Iraqi sunflower oil biodiesel is promising in reducing harmful emissions especially carbon dioxide and unburned hydrocarbon without impairing engine performance. It very useful information for engineers, scientists and industries to enhance sustainability of energy and pollution in Iraq or alike environment. By referring to the data, it was found that with an increasing concentration of biodiesel added in fuel, the BSFC was higher due to lower Calorific value while BP and BTE were slightly inferior compared to diesel. Fuel molecules accelerate oxidation reactions to produce combustibles, so both UBHC and $\mathrm{CO}_2$ emissions lees vastly at most of the tested points. Nevertheless, at the high load and speed conditions, $\mathrm{NO}_{\mathrm{x}}$ emissions were increased due to greater cylinder temperatures and longer duration for combustion with higher biodiesel content. These findings were distilled from earlier assessments and showed considerable robustness based on comparisons with joint previous research on cottonseed, soybean and other biodiesel feedstocks. BSFC increase for sunflower biodiesel (35%) is slightly higher at 30–32% compared to cottonseed and soybean. The $\mathrm{CO}_2$ reduction was similar at 50% not far from a range of 47–50% in another study and the $\mathrm{NO}_{\mathrm{x}}$ increase (21.3%) fell within a 17–25% reported range. Mainly these common features, also indicate the general applicability of the trends to a wide variety of biodiesel feed stocks.

Based on findings above, following recommendations proposed:

-Such real operating conditions can be modelled more accurately only under more experiments on transient driving cycles.

-In the future, investigations should also consider the impact of mitigation measures for reducing $\mathrm{NO}_{\mathrm{x}}$ emissions such as EGR or selective catalytic reduction (SCR).

-The importance of measuring PM levels in biodiesel-diesel blends for assessing fuel performance, fuel quality and environmental impact. PM measurement values may also facilitate the creation of improved engineered high-heating value fuel combinations having a smaller emissions impact than conventional fuels.

-Comparative study of the different biodiesels from different source under standard modes give a broader range of performance and emission data.

-The durability and compatibility of Biodiesel blends with conventional diesel engines must be evaluated based on long-term endurance tests.

In summary, sunflower biodiesel and blends are promising renewable fuel candidates to significantly lower CO and UBHC emissions. On the other hand, the penalty of high BSFC and $\mathrm{NO}_{\mathrm{x}}$ emissions demands a search for blending regulations and emission control technology.