Dual Fuel Research Articles

Investigation of The Effects of BD35 (Biodiesel/Diesel Blend) and Propanol Usage in Combustion Characteristics in A Dual Fuel Diesel Engine

This study investigates the changes in the combustion characteristics of a diesel engine modified to operate in reactivity controlled compression ignition mode using propanol as low reactivity fuel and BD35 as high reactivity fuel. In the study, BD35 fuel, a blend of 35% biodiesel and 65% petroleum-derived diesel, was sprayed directly into the cylinder as a high reactivity fuel, while propanol was sprayed into the intake manifold at low pressure as a low reactivity fuel for reactivity controlled compression ignition. Four different low reactivity fuel premixed ratios of 0%, 15%, 30% and 45% propanol were used in the experiments. The experiments were carried out under 60% engine load and 2400 (rpm) constant engine speed conditions. According to the data obtained, it was found that the maximum in-cylinder pressure value increased with the increase in the premixed ratio and a significant increase occurred especially when 45% premixed ratio was used. Although the use of propanol as low reactivity fuel in the test engine under the reactivity controlled compression ignition concept was observed to cause a decrease in the indicated mean effective pressure, the rate of decrease in the indicated mean effective pressure was found to slow down as the premixed ratio increased. Finally, it was found that the in-cylinder gas temperature decreased significantly with increasing the propanol premixed ratio. When all the findings are analyzed, it has shown an important way to understand the effects of propanol as low reactivity fuel and BD35 as high reactivity fuel on engine performance at high load in diesel engines modified to operate in reactivity controlled compression ignition mode.

Integration of a Belt Starter Generator in a Flex-Fuel Vehicle

<div>The concern with global warming has led to the creation of legislation aimed at minimizing this phenomenon. As a result, the development of technologies to minimize vehicle emissions and reduce fuel consumption has gained market share. A promising alternative is the use of a belt starter generator (BSG): an electric machine to replace the vehicle’s alternator. This research analyzes the effects of introducing a 12 V BSG into a flex-fuel vehicle, specifically examining its impact on fuel economy and CO<sub>2</sub> emissions when using both gasoline and ethanol. The utilization of a low-voltage BSG in a flex-fuel vehicle has not been previously studied. Numerical simulations and experimental fuel consumption and CO<sub>2</sub> emissions tests were performed for the normal production flex-fuel baseline configuration and the vehicle with the 12 V BSG, following the standards ABNT NBR 6601 and ABNT NBR 7024. The use of the BSG led to a 10.06% reduction in CO<sub>2</sub> emission in the urban cycle for the vehicle running on gasoline and a 6.28% reduction in energy consumption in the combined cycle. The results demonstrated that the low-voltage BSG is a promising solution for reducing fuel consumption and GHG emissions in flex-fuel vehicles. The electrical machine installation required minimal modifications to the vehicle and had a low adaptation cost. The BSG can also improve vehicle performance and drivability.</div>

Shape/penetration analysis and comparisons of isolated spray plumes in a multi-hole Diesel spray

Fuel injection systems significantly impact the combustion process and play a key role in reducing harmful exhaust emissions in internal combustion engines. For dual-fuel (DF) engines operating in gas mode, ignition of the main fuel is typically controlled by directly injected liquid pilot fuel. Liquid pilot fuel’s initial penetration and total mass considerably impact exhaust emissions and combustion stability. We investigated the spray morphology of a multi-hole diesel fuel injector within a constant-volume spray chamber using high-speed shadowgraphy and Mie-scattering measurements. Two methodologies were employed. The first one utilized a nozzle equipped with a thimble structure to isolate a single plume. The second methodology known as plume-blocking, involved sealing the orifices of the multi-hole nozzle to generate a single-spray plume. Our findings revealed that the plume-blocking approach demonstrated greater penetration than the thimble-equipped nozzle. The rapid penetration of this method may restrict its applicability to single-spray studies. Sprays generated from this partially sealed nozzle exhibited noticeable disparities compared to an unblocked nozzle, whereas a nozzle equipped with a thimble produced similar outcomes to the standard nozzle. The orifices when sealed, modify the flow distribution within the sac volume, which consequently affects the spray characteristics. In summary, this research provides insights into the impacts of various plume isolation methods on spray morphology, thereby enhancing the understanding of spray behaviour in transient conditions by comparing plume variations and disturbances under various fuel pressure and ambient conditions.

Scientific Research on Bioethanol in Brazil: History and Prospects for Sustainable Biofuel

Despite the recent need for sustainable energy resources, bioenergy gained its spotlight in the 2000s. Sugarcane is a significant crop in terms of sugar and energy capacity, and it can be an alternative energy source to mitigate the effects of climate change. Bioenergy production from sugarcane in Brazil is one of the most efficient options. This production lends a centrality to biofuels’ importance in confronting climate change effects. The present article reviews the Brazilian history of this crop as a biofuel source, focusing on plants as a biomass. We highlight the historical changes related to scientific, technological, industrial, and environmental advances since the beginning of the 20th century. We describe how creating governmental institutes and disseminating scientific knowledge strengthened public policies that led Brazil to occupy leadership positions in producing, distributing, and using bioenergy throughout the country. The compiled data show the improvements and the new approaches needed to improve ethanol sugarcane use. We performed a bibliometric analysis to evaluate Brazilian science’s contribution to this process compared to other countries. Brazil’s history of science and investment in sugarcane biofuel development for transportation may be divided into two phases: ethanol-only and flex-fuel cars. A third phase is starting, directed to the SAF and ethanol-to-hydrogen era.

A Comparative Experimental Analysis of Natural Gas Dual Fuel Combustion Ignited by Diesel and Poly OxyMethylene Dimethyl Ether

A Comparative Experimental Analysis of Natural Gas Dual Fuel Combustion Ignited by Diesel and Poly OxyMethylene Dimethyl Ether

Combustion Characteristic Prediction of Dual Direct Injection Fuel (Diesel-Propane) on RCEM Based on an Artificial Neural Network Approach

Studies from around the world show that engines using biofuel, LPG, and CNG emit fewer pollutants than those using conventional fuels. Experimental research has focused on a rapid compression and expansion machine (RCEM) that resembles a compression ignition (CI) engine. It uses dual direct injection fuel, diesel and propane (DP), with propane injection timing varying from 0 to 40 before top dead center (BTDC) and diesel injection timing remaining at 10 BTDC. The compression ratio was changed at points 17 and 19 by adjusting the RCEM connecting rod. A converge simulation program was used to run the simulation model, which was used to examine how the fire and inflow inside the chamber developed. The ANN method was used to predict pressure, temperature, power, TKE, and ITE data output based on propane energy fraction, compression ratio, and SOI of propane as input data parameters. It was noticed that the ANN prediction on experimental data has a higher accuracy compared to the simulation prediction. The R and MSE values were used to identify the accuracy of the prediction on output parameter data. ANN generalization capability is comparatively high when trained with large enough databases. The highest accuracy of prediction was produced on TKE, which had an MSE of 0.003715 and R value of 0.99981 from 287900 sample data. This shows that the ANN model is quite accurate in forecasting output experimental data.

Exploring Hydrogen-Enriched Fuels and the Promise of HCNG in Industrial Dual-Fuel Engines

This paper presents a theoretical analysis of the selected properties of HCNG fuel calculations and a literature review of the other fuels that allow the storage of ecologically produced hydrogen. Hydrogen has the most significant CO2 reduction potential of all known fuels. However, its transmission in pure form is still problematic, and its use as a component of fuels modified by it has now become an issue of interest for researchers. Many types of hydrogen-enriched fuels have been invented. However, this article will describe the reasons why HCNG may be the hydrogen-enriched fuel of the future and why internal combustion (IC) piston engines working on two types of fuel could be the future method of using it. CO2 emissions are currently a serious problem in protecting the Earth’s natural climate. However, secondarily, power grid stabilization with a large share of electricity production from renewable energy sources must be stabilized with very flexible sources—as flexible as multi-fuel IC engines. Their use is becoming an essential element of the electricity power systems of Western countries, and there is a chance to use fuels with zero or close to zero CO2 emissions, like e-fuels and HCNG. Dual-fuel engines have become an effective way of using these types of fuels efficiently; therefore, in this article, the parameters of hydrogen-enriched fuel selected in terms of relevance to the use of IC engines are considered. Inaccuracies found in the literature analysis are discussed, and the essential properties of HCNG and its advantages over other hydrogen-rich fuels are summarized in terms of its use in dual-fuel (DF) IC engines.

Computational Investigation of the Influence of Combustion Chamber Characteristics on a Heavy-Duty Ammonia Diesel Dual Fuel Engine

In response to increasingly stringent emissions regulations and the depletion of conventional fuel sources, integrating carbon-free fuels into the transport sector has become imperative. While hydrogen (H2) presents significant technical challenges, ammonia (NH3) could present a better alternative offering ease of transport, storage, and distribution, with both ecological and economic advantages. However, ammonia substitution leads to high emissions of unburned NH3, particularly at high loads. Combustion chamber retrofitting has proven to be an effective approach to remedy this problem. In order to overcome the problems associated with the difficult combustion of ammonia in engines, this study aims to investigate the effect of the piston bowl shape of an ammonia/diesel dual fuel engine on the combustion process. The primary objective is to determine the optimal configuration that offers superior engine performance under high load conditions and with high ammonia rates. In this study, a multi-objective optimization approach is used to control the creation of geometries and the swirl rate under the CONVERGETM 3.1 code. To maximize indicated thermal efficiency and demonstrate the influence of hydrogen enrichment on ammonia combustion in ammonia/diesel dual fuel engines, a synergistic approach incorporating hydrogen enrichment of the primary fuel was implemented. Notably, the optimum configuration, featuring an 85% energy contribution from ammonia, outperforms others in terms of combustion efficiency and pollutant reduction. It achieves over 43% reduction in unburned NH3 emissions and a substantial 31% improvement in indicated thermal efficiency.

Improving Sustainability in Urban and Road Transportation: Dual Battery Block and Fuel Cell Hybrid Power System for Electric Vehicles

Improving Sustainability in Urban and Road Transportation: Dual Battery Block and Fuel Cell Hybrid Power System for Electric Vehicles

Studies on Biodiesel and Hydrogen Powered Dual Fuel Common Rail Direct Injection Engine

Objectives: To evaluate the effect of hydrogen and used temple oil biodiesel (BTO) combination on the performance of Common Rail Direct Injection (CRDi) engine. To report the maximum possible flow rate (HFR) for knock free operation of the engine at a speed of 1500 RPM. Methods: Transesterification process was used to get BTO. was inducted through intake manifold. BTO was injected into engine cylinder using electronically controlled technique. Findings: The study revealed that the peak HFR was for BTO and 0.24 for diesel at an Injection Pressure (IP) of 800 bar and Injection Timing (IT) of before top dead center (bTDC). The Dual Fuel (DF) CRDi engine with Toriodal Reentrant Combustion Chamber (TRCC) shape yielded 6% to lower Brake Thermal Efficiency (BTE) with reduced exhaust gas emissions except 19 to higher oxides of nitrogen (NOx) at and 100% loads. Both Peak Combustion Pressure (PP) and Heat Release Rate (HRR) were 5 to 9% higher than BTO run diesel engine operation. Combustion Duration (CD) and Ignition Delay (ID) were 6 to 15% lower in DF CRDi operation with . Novelty: Diesel engine comes with hemispherical combustion chamber (HCC). Toriodal Reentrant Shaped Combustion Chamber (TRCC) was adopted in place of HCC which results better mixing of air and fuel. and BTO combination was used to power CRDi engine. Electronically controlled fuel injection system developed and fitted to conventional diesel engine. Keywords: Used temple oil biodiesel (BTO); Common rail direct injection (CRDi) engine; Toriodal reentrant combustion chamber (TRCC); Hydrogen flow rate (HFR); Hydrogen-biodiesel energy ratio (H2BER)

LPG-Diesel Dual Fuel Emission Characteristics: A Review

The global shift away from fossil fuels for energy, driven by concerns about emissions and energy security, has sparked significant interest in alternative fuels. One promising approach involves combining alternative fuels, like Liquefied Petroleum Gas (LPG), with traditional diesel engines. This strategy, known as the dual-fuel concept, aims to harness the strengths of each fuel type while reducing emissions and improving engine performance. This review focuses primarily on LPG as a dual fuel for diesel engines. LPG, a gaseous fuel primarily composed of propane and butane, offers substantial environmental benefits, including a 15% reduction in CO2 emissions, a 30% reduction in CO emissions, and a 50% reduction in NOx emissions compared to diesel. However, using pure LPG in diesel engines faces a challenge related to its ignition behavior. This challenge can be overcome by blending LPG with substances like Hydrotreated Vegetable Oil (HVO) or diesel fuel, which act as ignition enhancers. The main goal of this review is to provide a comprehensive overview of the potential advantages and applicability of the dual-fuel system combining diesel and LPG. It will explore various experimental setups, designs, and injection techniques, presenting diverse findings related to both engine performance and emissions. Additionally, the review will discuss additives that can further improve the combustion process. Overall, the research highlights the promising role of LPG as a dual fuel in reducing emissions and enhancing the efficiency of diesel engines, contributing to a more sustainable energy future.

Computational investigation of equivalence ratio effects on performance and emissions in a dual-fuel homogeneous charge compression ignition (HCCI) engine with 90% n-dodecane and 10% ethanol

As the automotive industry seeks environmentally friendly and fuel-efficient solutions, a significant transformation towards the Dual Fuel Homogeneous Charge Compression Ignition (DF-HCCI) Engine. It emerges as a highly promising and revolutionary approach to internal combustion engines. This paper provides a comprehensive Computational Investigation on the influence of Equivalence Ratio (ϕ) variations on the performance and emissions of a DF-HCCI engine, utilising a blend of 90% n-dodecane (premix) and 10% ethanol (spry injection). Through simulations, the study explores ϕ ranging from 0.45 to 0.70, providing a detailed analysis of their impact on crucial engine parameters. Results indicate a non-monotonic behaviour in piston work, with an initial increase followed by a decline beyond an optimal point due to incomplete combustion. CO emissions exhibit a general increase with higher ϕ, attributed to reduced air availability for complete combustion. CO2 emissions display a non-monotonic trend, peaking at ϕ = 0.5, indicative of a complex interplay between combustion temperature and completeness. NOx emissions decrease with rising ϕ, as higher temperatures favour NOx formation. Soot emissions decrease with increasing ϕ , correlating with lower combustion temperatures. This investigation provides insights into the relationship between ϕ and DF-HCCI engine characteristics, offering an optimising engine efficiency and mitigating environmental impact.

Research on Dual Fuel Combustion Characteristics of PFI Natural Gas +DI Gasoline in Large Cylinder Diameter Engine

A 3D simulation model of a single cylinder of a natural gas engine was established. PFI natural gas DI gasoline was used to control the time matching between injection and ignition, so that gasoline could form a small active stratified area near the spark plug. The combustion characteristics under different matching conditions were studied, and finally compared with pure natural gas. It is found that gasoline can be used in large cylinder diameter natural gas engine in a small range, which can accelerate the combustion of natural gas fuel, shorten the time used by CA0-CA5 by 77.6%, shorten the time used by CA5-CA90 by 26.5%, and increase the indicated thermal efficiency of natural gas engine by 1.4%.

Comparative analysis of Gasifier-CI engine performance and emissions characteristics using diesel with producer gas derived from coal– briquette-coconut shell-mahua feedstock and its blends

In this study, gasifier-dual fuelled engine (G-DFE) performance was conducted and compared together with gasification of individual feedstock (i.e., mahua wood, coconut shell, sawdust briquette) and their blends with low-grade coal. Additionally, the performance of different sets of feedstock gasification and engine utilization were compared with optimal input and output response using response surface methodology (RSM). The inputs of G-DFE include gasification equivalence ratio (GER) and engine load percentage. The G-DFE performance includes engine brake thermal efficiency (BTE), diesel saving (DS), and CO, CO2, HC, and NOX emissions. Results depict biomass co-gasification blends presented higher engine performance than single feedstock gasification. The (briquette + mahua) producer gas (PG) based dual fuel (DF) engine offers a maximum BTE of 27.6% at input condition of GER 0.12 and 100% load. The maximum DS of 63.44% was obtained for coconut shell G-DFE. Regarding optimum emission, the maximum CO and HC, belong to the setting of GER 0.10 for briquette and (briquette + mahua) G-DFE. The maximum CO2 and NOX belong to the setting of GER 0.10, 100% load for (briquette + mahua), and GER 0.43, 100% load for mahua G-DFE, respectively. Further, the study's experimental results and optimizations can guide G-DFE management for improved operation and reduced environmental footprint.

Effect of Injection Timing on the Dual Fuel Engine Performance Operated with Hydrogen and Nano-Biodiesel Blends

In the current work, effect of nano-biodiesel blends and injection timing on the performance of hydrogen fueled dual fuel (DF) engine is presented. Hydrogen flow rate is maintained constant with a flow rate of 0.15 kg/h. For this B20 and nano-blends of Nigella sativa oil methyl ester (NLSTVAOME) and Jack fruit seed oil methyl ester (JKFSOME) fuel combinations are used. Nano-blends of respective B20 biodiesels are prepared using graphene amine (GA) nanoparticles with varied proportions ranging from 60 to 100 ppm using probe sonication method. Stabilization of the nano-blends are ensured with reference to quantity of nanoparticle, surfactant SDS (Sodium Dodecyl Sulfate) used and sonication time. Addition of the nanoparticles in the B20 biodiesel blends till 80 ppm showed considerable improvements on the performance of diesel engine with single fuel operation due to improved combustion compared to B20 biodiesel blends. Beyond 80 ppm the performance deteriorated due to non-homogeneous mixtures of nano-biodiesel blends. Injection timing (IT) for the modified DF engine IT is varied from 19 to 31oBTDC in steps of 4oBTDC. Further advancing the IT from 19 to 27oBTDC showed improved dual fuel engine performance with B20+GA80 blends of both biodiesels along with hydrogen induction when compared to B20 operation. Further mixing of air-hydrogen in the inlet manifold of dual fuel engine is studied using CFD analysis for varied hydrogen flow rates ranging from 0.10 to 0.2 kg/h in steps of 0.05 kg/h.

Artificial neural network models for forecasting the combustion and emission characteristics of ethanol/gasoline DFSI engines with combined injection strategy

Ethanol was a viable alternative and renewable fuel for spark ignition engines, and ethanol/gasoline dual-fuel combustion with combined injection strategy can strengthen the benefits of using ethanol in engines. However, delicate calibration and optimization were required for ethanol/gasoline DFSI engines due to their higher control complexity and flexibility. Therefore, Artificial Neural Network (ANN) models were developed to represent the performance of DFSI engines. This study established the architecture for the ANN models of ethanol/gasoline DFSI engines, and the topology of 8-36-24-3, 8-64-70-6, 8-48-48-3, and 8-36-16-2 were suggested for the modeling of performance, combustion characteristics, gaseous and PN emissions, respectively. The non-linear relationship between the core control variables and performance, combustion, and emission characteristics of ethanol/gasoline engines can be accurately mapped by the proposed ANN models. The regression values were within the range of 0.9387–0.9962, and the mean square relative errors were within the range of 0.000184–0.03935 between the ANN predicted and experimentally measured results. Moreover, the ANN models had the advantages of high accuracy, sound model completeness, superior robustness, and satisfied reliability, which were desirable for the calibration and optimization of engines.

Tracing the regulated emissions of field-aged gasoline/natural gas bi-fuel taxis from new to 160,000 km: Deterioration and environmental implications

Natural gas (NG) is considered an economically viable transport decarbonization option, especially for developing countries. However, as per the ongoing European and Chinese vehicle emission regulations, the durability and in-service compliance tests of the exhaust emissions from gasoline/NG bi-fuel vehicles are only mandated in gasoline mode, leaving the real-world emission performance of NG fueling at risk. To bridge this gap, the exhaust emissions from five gasoline/NG bi-fuel taxis were traced from new (less than 10,000 km) to 160,000 km after every 10,000 km of field driving. Both room-temperature cold-start and warm-start chassis dynamometer tests were performed over the certification drive cycle. This tracing study lasted for 3.5 years and covered the variations of seasons, routine services, and minor repairs. The results manifested that compared to gasoline fueling, NG had statistically lower carbon monoxide before 100,000 km of driving but higher total hydrocarbon and nitrogen oxides emissions throughout the useful life in both cold- and warm-start tests. By applying linear regression to the data points obtained across the 160,000 km tracing, NG fueling showed a noticeably quicker deterioration with mileage than gasoline. However, given that gasoline and NG modes shared the same catalysts, this is attributed to the less careful calibration of NG mode predominantly because of the void of regulatory requirements. On average, NG fueling produced about 20 % less carbon dioxide emissions than gasoline, but the observed fuel leakage in NG mode partially offset the global warming potential advantage. Overall, NG sees benefits and challenges in mitigating vehicle-related environmental issues. To better control this risk, it is strongly recommended that in future regulations, the durability and in-service compliance requirements of NG fueling shall be complemented, and fuel leakage shall be included in the control of evaporative emissions.

Experimental and molecular dynamics study on micro-explosion of water-in-diesel droplets in the presence of solid nanoparticles

In recent years, multicomponent fuels have been widely studied; among them, dual fuels with different boiling points have attracted attention because of the micro-explosion phenomenon, which makes the mixing and combustion of diesel and air more complete. Strengthening the micro-explosion processes and further improving the degree of mixing of diesel and air is one of the core problems of micro-explosions. This study conducted experiments and molecular dynamics simulation to investigate this problem by adding nanoparticles to emulsified water-in-diesel droplets. First, the concept of puffing was proposed to describe the time and difficulties of bubble nucleation. Second, frequency distributions of a single micro-explosion intensity were proposed, and S-n diagrams comprising the cumulative micro-explosion intensity and total micro-explosion frequency were used to describe the micro-explosion intensity comprehensively. The results show that nanoparticles promote heat transfer between the droplets and high-temperature environments. Moreover, it weakens the potential energy between liquid water molecules and generates bubble nuclei around the nanoparticles, decreasing the bubble nucleation temperature and time and increasing bubble occurrence probability. Furthermore, the micro-explosion mode gradually shifts from low frequency (intensity) to medium frequency (intensity) with increasing carbon nanoparticle concentration.

Engine-out emissions from an ammonia/diesel dual-fuel engine – The characteristics of nitro-compounds and GHG emissions

In the transportation sector, ammonia used as a power source plays a significant role in the scenario of carbon neutralization. However, the engine-out emissions correlations of ammonia-diesel dual-fuel (DF) engines are still not totally clear, especially the nitro-compounds of great concern and GHG. In this study, the engine-out emissions are evaluated by using a four-cylinder pilot diesel-ignited ammonia DF engine. Various operating conditions consisting of ammonia energy ratio (AER), engine load, and speed were carried out. Unburned NH3 increases with raising ammonia content but decreases with increasing engine load and speed. The NO + NO2 tendency shows a non-linearity trend with increasing ammonia content, while a trade-off correlation is linked to N2O. The 20 % and 70 % decarbonization targets need 40 % and 80 % ammonia energy without regard to N2O’s effect, while at least 60 % and 90 % ammonia energy respectively with considering N2O. N2O presents a parabolic-like tendency with AERs. Advanced pilot-diesel injection timing helps to reduce both NH3 and N2O, but this effect becomes insignificant as the AER is less than 0.4. A combustion optimization strategy of the rapid heat release and ammonia-governed heat release respectively are revealed. The possible emission improvements are discussed in detail.

Impact of spray interaction on ammonia/diesel dual-fuel combustion and emission under engine relevant conditions

This study investigates the combustion characteristics of ammonia and diesel sprays in a constant-volume vessel under conditions typical of internal combustion engines, focusing on the interplay between evaporation dynamics and flame interactions within the framework of the Direct Dual Fuel Stratification (DDFS) concept. Under non-evaporation conditions, ammonia and diesel sprays exhibit comparable evaporation profiles, but under evaporation scenarios, ammonia’s higher evaporation rate results in faster mixing with ambient gas than diesel despite the similar liquid penetration lengths of these two fuels. By utilizing meticulously designed arrangements of diesel and ammonia spray injectors, two distinct interaction scenarios between diesel spray and ammonia spray, early and late interaction, are explored. In the early interaction scenario, fuel-rich ammonia-air mixtures ignite directly by the diesel flame, achieving self-sustained propagation and significant heat release, thereby maintaining a high-temperature region for continuous combustion. Conversely, in late interaction scenarios, rapid ammonia evaporation leads to a fuel-lean ammonia/air mixture that cannot be ignited by the diesel flame, eventually leading to ammonia flame extinction. The study reveals that NOx and N2O emissions are sensitive to the diesel/ammonia flame interaction. N2O emissions, formed predominantly at the forefront of the quenching ammonia flame, pose a significant challenge due to the fast evaporation rate and slow oxidation rate in fuel-lean mixtures. These findings provide insights into the physics of ammonia–diesel combustion, highlighting the challenges and potential strategies for efficient and clean combustion in ammonia-fueled DDFS engines.