Ammonia-diesel dual-fuel combustion mode is one of the potential ways to achieve lower carbon emissions in compression ignition engines. In this work, the effects of ammonia addition on diesel combustion characteristics were experimentally investigated in an optical CI engine. The gaseous ammonia is introduced to the engine through a port injection while diesel is directly injection into the cylinder. A color high-speed camera was utilized to detect and differentiate between diffusion burning and lean-premixed ammonia combustion. Additionally, computational models were conducted and the findings were coupled with the experimental data. According to optical investigations, the lift-off distance is created during the diesel spray and progressively grows as the ammonia energy ratio (AER) rises. The findings indicate that, in comparison to pure diesel combustion mode, combustion in an ammonia environment exhibits prolonged ignition delay duration and lesser flame luminosity. Secondly, a multi-injection strategy for diesel fuel was used where the diesel pre-injection timing (SOPI) values adjusted from −30 °CA ATDC to −60 °CA ATDC). Advancing SOPI is an effective approach to suppress diesel diffusion flame and reduce soot production in the cylinder. For advanced SOPI, findings reveal that rich pockets have decreased drastically as the combustion progresses. With the advancement of SOPI, there is a notable a connection between the flame speed and the peak heat release rate, where a high flame speed correlates to a greater heat release rate peak. Finally, the ratio of pre-injection of diesel fuel (ROPI) varied from 0 to 100% as a mean to improve flame propagation. There is a crucial threshold of pre-injection (ROPI) mass ratio of 45%, at which the initial flame features alter considerably. As the ROPI exceeds 45%, the flame kernel appears as a visible flame near to the main injection timing (SOMI), indicating that the ignition delay duration is decreasing. 

On ammonia/diesel dual-fuel combustion in optical engine

Effects of ambient density and injection pressure on ignition and combustion characteristics in diesel spray under plateau cold-start conditions

Ammonia/coal co-firing in coal-fired power plants is an effective way to achieve CO2 reduction. In this paper, the ammonia/coal co-firing study was carried out in a 45kW wall-temperature-controlled staged combustion downstream furnace at 1100 °C. Bituminous coal was used as the experimental object to analyze the effects of ammonia injected at the main combustion zone, reduction zone, with the burnout air, and at the burnout zone on NO release characteristics at different ammonia co-firing ratios. To ascertain the significant reaction of NO production in the ammonia/coal co-firing, chemical reaction kinetics calculations were performed. When co-firing ratios of 10∼30%, the NO emission concentration is lower by the ammonia injection position of the main combustion zone which is 275–346 mg/m3. When co-firing ratios reach to 40% and 50%, NO releases are lower by the ammonia injection position of burnout zone which is 511–574 mg/m3. In addition to exhibiting a greater capacity to decrease NO in environments with low oxygen concentrations and high NO concentrations, ammonia can also, under specific circumstances, have a significant capacity to decrease NO in environments with high oxygen concentrations. Based on the experimental results and chemical kinetic calculations, the NO release pattern and mechanism during ammonia-coal co-combustion with different ammonia injection methods under air staged combustion were investigated, which provides a technically feasible solution to reduce CO2 and NOx emissions from coal-fired power plants. 

Experimental study and kinetic analysis of NO emission characteristics in ammonia/coal co-firing process with different ammonia injection methods

Experimental and kinetic studies of the mutual oxidation of ammonia and n-dodecane at low to high temperatures

To meet climate targets, a global shift away from fossil fuels is essential. For sectors where electrification is impractical, it is crucial to find sustainable energy carriers. Renewable methanol is widely considered a promising fuel for powering heavy-duty applications like shipping, freight transport, agriculture, and industrial machines due to its various sustainable production methods. While current technological efforts focus mainly on dual-fuel engines in shipping, future progress hinges on single-fuel solutions using renewable methanol to achieve net-zero goals in the heavy-duty sector. This review examines the research status of technologies enabling methanol as the sole fuel for heavy-duty applications. Three main categories emerged from the literature: spark-ignition, compression-ignition, and pre-chamber systems. Each concept’s operational principles and characteristics regarding efficiency, stability, and emissions were analyzed. Spark-ignition concepts are a proven and cost-effective solution with high maturity. However, they face limitations due to knock issues, restricting power output with larger bore sizes. Compression-ignition concepts inherently do not suffer from end-gas autoignition, but encounter challenges related to ignitability due to the low cetane number of methanol. Nonetheless, various methods for achieving autoignition of methanol exist. To obtain stable combustion at all load points, a combination of techniques will be required. Pre-chamber technology, despite its lower maturity, holds promise for extending the knock limit and enhancing efficiency by acting as a distributed ignition source. Furthermore, mixing-controlled pre-chamber concepts show potential for eliminating knock and the associated size and power limitations. The review concludes by comparing each technology and identifying research gaps for future work.

Renewable Methanol as a Fuel for Heavy-Duty Engines: A Review of Technologies Enabling Single-Fuel Solutions

Effects of operating parameters on start performance of compression ignition engine by using high-pressure direct-injection pure methanol fuel

Due to the challenges of ammonia, such as high ignition energy and slow flame propagation speed, the utilization of ammonia in engines might necessitate the implementation of dual-fuel combustion modes along with the use of cetane improvers. To optimize the performance of ammonia-fueled engines, and achieve efficient and clean combustion, three-dimensional computational fluid dynamics (CFD) simulations are imperative. However, prior to conducting a three-dimensional CFD study, an accurate reaction mechanism for each component is essential. In this study, the blending mechanisms of ammonia, n-dodecane, and 2-ethylhexyl nitrate (EHN) were constructed using CHEMKIN software, including 243 species and 1293 reactions. The calculated results of ignition delay, laminar flame velocity, and the concentration of significant species agreed well with experiment results. The ignition delay, laminar flame velocity, adiabatic flame temperature, and the concentration of major products were analyzed in different blending ratios. The use of high cetane fuel shortens ignition delay and increases laminar flame speed. As the equivalence ratio of ammonia increases, the concentration of NO decreases while the concentration of H2 increases. The combustion process is also analyzed based on optical diagnostic results, and the impact of the ammonia/n-dodecane mixtures blended with EHN on the combustion process is investigated. The addition of EHN proved to shorten the ignition delay of the mixture. Furthermore, the introduction of EHN exhibits marginal influence on NOx generation, with the predominant augmentation of NOx emissions stemming from fuel-derived NOx resulting from the fuel's inherent nitrogen content.Due to the small amount of EHN added, the overall impact is relatively small. 

Combustion mechanism study of ammonia/n-dodecane/n-heptane/EHN blended fuel

A novel method to chemically convert waste PET plastic into high–value monolithic materials with excellent flame retardancy, mechanical strength and hydrophobicity

Numerical Simulation of the High-Boosting Influence on Mixing, Combustion and Emissions of High-Power-Density Engine

Methanol has attracted much attention because it can realize carbon neutral cycle. Methanol is difficult to use in compression ignition engines because of its low cetane number and high latent heat of vaporization. 2-ethylhexyl nitrate (EHN) is a widely used cetane number improver, which can effectively promote the ignition of methanol. Therefore, a reduced mechanism of methanol and EHN containing 61 species and 479 reactions is proposed in this paper, and it has been verified to fit well with the original mechanism and experimental date. Then, chemical kinetic analysis is carried out using CHEMKIN PRO. Results show that after adding EHN, the ignition delay is significantly shortened. As the EHN ratio increases, the effect of EHN on shortening the ignition delay period does not increase nonlinearly, but shows a slowing trend. The reaction with higher positive temperature sensitivity changes from R133 (CH3OH + HO2 = CH2OH + H2O2) to R307 (CH2O + NO2 = HONO + HCO), and the reaction with higher negative temperature sensitivity changes from R18 (2HO2 = H2O2 + O2) to R305 (HCO + NO2 = HONO + CO). The reaction time of H, OH and HO2 is advanced and the peak values decrease. In the methanol dehydrogenation pathway, the proportions of reactions involving HO2 decrease significantly and the proportions of reactions involving NO2 and OH increase. The methanol consumption rate increases significantly after adding EHN. With the addition of 3% EHN, the reaction time of methanol was reduced by 99.8% compared to pure methanol. 

Study on the mechanism of influence of cetane improver on methanol ignition

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