Influence of Hydrogen on the Performance and Emissions Characteristics of a Spark Ignition Ammonia Direct Injection Engine

Abstract

Because ammonia is easier to store and transport over long distances than hydrogen, it is a promising research direction as a potential carrier for hydrogen. However, its low ignition and combustion rates pose challenges for running conventional ignition engines solely on ammonia fuel over the entire operational range. In this study, we attempted to identify a stable engine combustion zone using a high-pressure direct injection of ammonia fuel into a 2.5 L spark ignition engine and examined the potential for extending the operational range by adding hydrogen. As it is difficult to secure combustion stability in a low-temperature atmosphere, the experiment was conducted in a sufficiently-warmed atmosphere (90 ± 2.5 °C), and the combustion, emission, and efficiency results under each operating condition were experimentally compared. At 1500 rpm, the addition of 10% hydrogen resulted in a notable 20.26% surge in the maximum torque, reaching 263.5 Nm, in contrast with the case where only ammonia fuel was used. Furthermore, combustion stability was ensured at a torque of 140 Nm by reducing the fuel and air flow rates.

Ammonia Can be Currently Considered as one of the Best Green Energy Ally

“…Natural gas engines are more suitable for retrofitting to ammonia-hydrogen operation due to their higher compression ratio and the lower dependence on fuel laminar flame speed of their combustion chamber [159]. However, there is a limit to the addition of hydrogen in the mixture based on the risk of backfire and wall heat losses [160]. Low levels of hydrogen addition allow stability improvement, acting as an ignition promoter and increasing laminar flame speed, but this single factor does not fully explain the improvement in operation achieved [161].…”

“…The use of ammonia as the only fuel in a spark ignition engine is practically unfeasible due to the difficulty of ignition, low flame stability, combustion efficiency, and power delivery, so dual fuel configuration seems the best option. Using hydrogen as a dual fuel in proportions between 10-15% allows for solving these problems [160,161]. The required hydrogen may be obtained from an additional storage tank or the partial dissociation of ammonia; in any case, it is necessary to use systems such as EGR to reduce ammonia and NO emissions [175].…”

Ammonia Can Be Currently Considered One of the Best Green Energy Allies

“…Natural gas engines are more suitable for retrofitting to ammonia-hydrogen operation due to their higher compression ratio and the lower dependence on fuel laminar flame speed of their combustion chamber [187]. However, there is a limit to the addition of hydrogen in the mixture based on the risk of backfire and wall heat losses [188]. Low levels of hydrogen addition allow stability improvement, acting as an ignition promoter and increasing laminar flame speed, but this single factor does not fully explain the improvement in operation achieved [189].…”

“…The use of ammonia as the only fuel in a spark ignition engine is practically unfeasible due to the difficulty of ignition, low flame stability, combustion efficiency, and power delivery, so dual-fuel configuration seems to be the best option. Using hydrogen as a dual fuel in proportions between 10 and 15% allows for solving these problems [188,189]. The required hydrogen may be obtained from an additional storage tank or the partial dissociation of ammonia; in any case, it is necessary to use systems such as EGR to reduce ammonia and NO emissions [203].…”

Evaluation of Control Strategy on Operation Range Expansion of High-Pressure Ammonia Direct Injection Marine Dual-Fuel Engine

“…To burn premixed ammonia air mixture, an ignition device with high ignition energy must be used or a stable ignition source must be used. 15 In particular, because the flammable limit of ammonia is not wide, the amount of intake air must be adjusted to form a mixture near the stoichiometric air−fuel ratio. 16 However, the combustion strategy presented in this study uses micropilot (MP) oil for ignition, which previous researchers ignored, and uses a diffusion flame similar to diesel by postinjecting ammonia fuel at high pressure.…”