1.Introduction

With the rapid advancement of the global economy, the energy demand continues to increase, while traditional fossil fuel reserves are steadily depleting. The considerable pollutants produced from their combustion have resulted in significant environmental harm. As a result, the development and adoption of renewable and clean alternative energy sources have become a worldwide imperative. Among renewable fuels, ammonia has emerged as a promising carbon-free energy carrier with mature infrastructure for production, storage, and transportation. Despite its poor combustion properties, Zhu and Shu [1] demonstrated that blending ammonia with combustion promoters enables its practical application in internal combustion engines while significantly reducing CO₂ emissions. Zhang et al. [2] developed an online big-data monitoring and assessment framework for evaluating IC engine performance with various biofuels, demonstrating that lamb fat biofuel (LFB) outperformed both waste cooking oil biofuel (WCOB) and conventional diesel across multiple performance indicators, including vibration characteristics, brake thermal efficiency, and friction power. As a renewable fuel, biodiesel is widely recognized as an effective solution to energy and environmental issues, owing to its superior combustion characteristics and lower emissions from incomplete combustion. Nonetheless, the differences in physicochemical properties between biodiesel and Traditional diesel can influence diesel engine performance and emissions. Consequently, thorough research into the effects of biodiesel on diesel engine performance and emissions is of considerable theoretical and practical significance.

2.Physicochemical Properties of Biodiesel

Biodiesel is a long-chain fatty acid monoalkyl ester [3] derived from the esterification of vegetable oils, animal fats, or waste oils. Its molecular structure is rich in oxygen atoms, which facilitates more effective oxygen uptake during combustion. This characteristic not only improves combustion efficiency but also reduces the formation of byproducts from incomplete combustion.

The importance of understanding fuel physicochemical properties extends beyond traditional biodiesel applications. Recent studies on alternative fuels have highlighted how fundamental properties such as density and viscosity critically influence spray formation and combustion characteristics. For instance, research on synthetic fuels has demonstrated that fuel density directly correlates with injection parameters, affecting the discharge coefficient and spray penetration patterns under various temperature conditions [4]. These findings underscore the universal significance of physicochemical properties across different fuel types.

Additionally, biodiesel differs from Traditional diesel fuel in terms of density, viscosity, and flash point, all of which have a significant influence on the injection systems and combustion processes of diesel engines. The physicochemical properties of B40 biodiesel are summarized in Table 1. Compared to standard diesel, B40 biodiesel maintains a normal cetane number, displays a slightly higher density, possesses lower kinematic viscosity, and achieves sulfur content levels well below those required by the National IV standard. Notably, its flash point remains within the standard range.

3.Influence of Biodiesel on Diesel Engine Performance

4.Influence of Biodiesel on Diesel Engine Emissions

5.Experimental Research

To further investigate biodiesel’s impact on diesel engine performance and emissions, this study conducted a series of experiments. The tests utilized a four-stroke direct-injection diesel engine. Following the methodology trends in alternative fuel research, our experimental approach incorporated comprehensive monitoring similar to Zhang, M.’s [2] big-data framework for biofuel assessment. This ensures reliable data collection for performance evaluation under various operating conditions. When comparing Traditional diesel with B40 (a 40% biodiesel-60% diesel blend), it is important to note that B40’s high sulfur content could lead to sulfur poisoning in copper-based SCR catalysts commonly used in National VI standards [10]. To avoid any adverse effects on SCR efficiency or exhaust emission analysis, the experiment utilized a National V vanadium-based SCR catalyst.

5.2.Experimental Results and Analysis

5.2.1.Power Output

Experimental results indicate that, when maintaining the original diesel engine combustion parameters and controlling key bench conditions (such as intake water temperature, fuel injection temperature, intercooler performance, and exhaust backpressure), the external characteristic power of the engine running on B40 biodiesel decreased by an average of 3.35% compared to Traditional diesel, as shown in Figure 1. This demonstrates that the use of biodiesel can reduce the power output of diesel engines to a certain extent.

Figure 1. Comparison of the external characteristic power of diesel engines.

5.2.2.Economy

Fuel consumption rate: Due to the slight decrease in power performance, we adjusted the engine combustion parameters to bring the power performance of diesel engines burning biodiesel back to traditional diesel levels. In the external characteristic test, a significant difference in fuel consumption was found. As shown in Figure 2, the fuel consumption rate deteriorated by 5.83% to 6.74%, with an average deterioration of 6.44%.

Figure 2. External characteristics fuel consumption comparison.

We also found a significant difference in fuel consumption between the European Steady-state Cycle (abbreviated as ESC in the following text) and the European Transient Cycle (abbreviated as ETC in the following text) according to the National V standard emission cycle. See Table 2 for relevant statistics of the National V standard cycle. In ESC and ETC cycles, B40 biodiesel consumes 0.947 kg and 0.625 kg more than traditional diesel, respectively, accounting for about 6.4% and 5.3%

Table 2.

Statistics of pollutant emission and fuel consumption of cycle engines according to the National V standard.

Recurrence	Diesel	NO x g/kWh	CO g/kWh	THC g/kWh	PM g/kWh	Recirculation Fuel Consumption kg
ESC	B40 biodiesel	9.552	0.062	0.008	0.009	15.705
	Traditional diesel	9.232	0.077	0.011	0.010	14.758
ETC	B40 biodiesel	9.086	0.314	0.006	0.011	12.448
	Traditional diesel	8.923	0.513	0.008	0.014	11.823

5.2.3.Engine Emission Characteristics

Nitrogen oxide (NO_x) emission: When using biodiesel blended fuel, the NO_x emission of diesel engines increases slightly. In the external characteristic test, it can be seen that the NO_x increases more with higher speed, as shown in Figure 3, with an average increase of about 5%.

Figure 3. Comparison of NO_x emissions in external characteristics.

We also found significant NO_x emission differences in the ESC and ETC cycles according to the National V standard emissions, as shown in Table 2. In the ESC cycle, B40 biodiesel has a NO_x ratio of 0.32 g/kWh larger than that of traditional diesel, accounting for about 3.5%; in the ETC cycle, B40 biodiesel has a NO_x ratio of 0.163 g/kWh larger than that of traditional diesel, accounting for about 1.8%.

Particulate matter (PM) emission: Through the National V standard emission cycle ESC and ETC, it can be found that B40 biodiesel can reduce certain particulate emissions, as shown in Table 2.

CO and THC emissions: Through the National V standard emission cycle ESC and ETC, it can be found that B40 biodiesel can reduce a certain amount of CO and THC emissions.

5.2.4.SCR Emission Characteristics

By comparing the SCR hardware and calibration with Traditional diesel, we analyzed the NO_x emission performance of B40 biodiesel under SCR treatment. As shown in Table 3, when combined with the original engine emission levels from Table 2, the NO_x emissions of B40 biodiesel showed a slight improvement compared to Traditional diesel. Specifically, the NO_x emission per kWh increased by 0.458 g/kWh during the ESC cycle and by 0.345 g/kWh during the ETC cycle.

Table 3.

NO_x data of cycle exhaust according to National V Standard.

Recurrence	Diesel Oil	NOx (g/kWh)	Exhaust Uniform Temperature (℃)
ESC	B40 biodiesel	1.581	376
	Traditional diesel	1.123	379
ETC	B40 biodiesel	1.280	326
	Traditional diesel	0.935	330

In addition to temperature, the main factors affecting the efficiency of National V SCR are NO₂ ratio. As shown in Figure 4, we found in the external characteristic test that the NO₂ ratio of B40 biodiesel is lower than that of traditional diesel oil by 1.04% on average and 19.6% relatively. The lower NO₂ ratio is the main reason why the NO_x discharged from SCR is slightly more than the original NO_x.

Figure 4. NO₂ Comparison of proportion.

6.Conclusions

The challenges identified in our B40 biodiesel study reflect broader trends in alternative fuel adoption. As Liu [11] noted in his editorial on alternative fuels in automotive vehicles, the development of cleaner energy sources requires balancing environmental benefits with practical performance considerations. The continued evolution of automotive manufacturing, as discussed by Zhang et al. [12] regarding lignocellulosic biomass applications, suggests that bio-based materials and fuels will play an increasingly important role in achieving carbon neutrality goals.

This study investigated the influence of biodiesel on diesel engine performance and emissions through both theoretical analysis and experimental evaluation. The key findings are as follows:

- Power output: B40 biodiesel reduces diesel engine power by approximately 3.35%.

- Fuel economy: Fuel consumption deteriorates by about 5% when using B40, indicating reduced fuel economy.

- Nitrogen oxides (NO_x): NO_x emissions increase with B40 biodiesel. Additionally, since National V SCR systems primarily use open-loop control, if the original diesel configuration has a minimal compliance margin, switching to B40 presents a risk of exceeding emission limits.

- Other pollutants: B40 biodiesel significantly reduces emissions of particulate matter (PM), hydrocarbons (HC), and carbon monoxide (CO).

- Sulfur content: The sulfur content in B40 biodiesel is excessively high and must be reduced before it is suitable for use with copper-based molecular sieve SCR systems.

- Given the observed decreases in power output, worsened fuel economy, and increased NO_x emissions, it is necessary to calibrate both the combustion parameters and the SCR system specifically for B40 biodiesel. While the reduction in PM, CO, and HC emissions offers notable environmental benefits, these advantages are more relevant for environmental protection than for meeting regulatory emission standards.

Author Contributions: Q.C.: Experimental testing, data organization, writing, verify. T.F.: Review. L.Z.: Edit, verify. S.Z.: Experimental testing. L.D.: Experimental testing. Z.C.: Funding Acquisition. All authors have read and agreed to the published version of the manuscript.

Funding: National Key Research and Development Program (2023YFC3707204).

Institutional Review Board Statement: Ethical review and approval were waived for this study due to its non-invasive computational nature.

Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.

Data Availability Statement: The data that support the findings of this study are available from the corresponding author upon reasonable request.

Acknowledgments: The author would like to thank Jinhua Wang for his support of experimental resources.

Conflicts of Interest: The authors declare no conflict of interest.

Use of AI and AI-Assisted Technologies: No AI tools were utilized for this paper.