Experimental Investigation of High-Pressure Liquid Ammonia Injection under Non-Flash Boiling and Flash Boiling Conditions

Abstract

Liquid ammonia is an ideal zero-carbon fuel for internal combustion engines. High-pressure injection is a key technology in organizing ammonia combustion. Characteristics of high-pressure liquid ammonia injection is lack of research. Spray behaviors are likely to change when a high-pressure diesel injector uses liquid ammonia as its fuel. This study uses high-speed imaging with a DBI method to investigate the liquid penetration, width, and spray tip velocity of high-pressure liquid ammonia injection up to 100 MPa. Non-flash and flash boiling conditions were included in the experimental conditions. Simulation was also used to evaluate the results. In non-flash boiling conditions, the Hiroyasu model provided better accuracy than the Siebers model. In flash boiling conditions, a phenomenon was found that liquid penetration and spray tip velocity were strongly suppressed in the initial stage of the injection process, this being the “spray resistance phenomenon”. The “spray resistance phenomenon” was observed when ambient pressure was below 0.7 MPa during 0–0.05 ms ASOI and was highly related to the superheated degree. The shape of near-nozzle sprays abruptly changed at 0.05 ms ASOI, indicating that strong cavitation inside the nozzle caused by needle lift effects is the key reason for the “spray resistance phenomenon”.

An Experimental Study on the Flash Boiling Characteristics of Liquid Ammonia Spray in a Constant Volume Chamber under High Injection Pressure

“…In the analysis, we set the spray to 0.4 ms as the node of the progress. Between the start of spray and 0.4 ms, the penetration distance of non-flash boiling spray grew faster than that of transient flash boiling spray, while the developments' speed of penetration of flare flash boiling spray is the slowest [21]. Before 0.4 ms, the penetration distance of the three sprays was the same at a certain time point.…”

“…In the analysis, we set the spray to 0.4 ms as the node of the progress. Between the start of spray and 0.4 ms, the penetration distance of non-flash boiling spray grew faster than that of transient flash boiling spray, while the developments' speed of penetration of flare flash boiling spray is the slowest [21]. Before 0.4 ms, the pen- In Figures 9 and 10, based on the comparison of gas and liquid penetration, the developing trend is roughly the same, despite that the liquid penetration fluctuates in different extents after above 0.4 ms of the injection, and does not significantly increase any more after the fluctuation.…”

“…After 0.4 ms, the STP of flare flash boiling spray significantly accelerated, and the growth rate was faster than that of other two kinds of sprays. Due to the low back pressure of flash boiling state, the STP of the fuel is abnormally shortened at a very low environmental density inside the vessel, which is named as "spray resistance phenomenon" [21]. In Section 3.2.2, this phenomenon will be discussed further.…”

“…At approximately 0-0.15 ms in the initial stage of spray process, the gas STP under flare flash boiling conditions were lower than that under cold conditions, although the ambient density under flare flash boiling conditions was lower than those under the non-flash boiling conditions. This is because, at P amb of 0.2 MPa, liquid ammonia which is filled with the spray hole generates intensive cavitation at the time when injector needle started lifting [21][22][23], this behavior will block the nozzle and cause a different tendency with a shorter penetration than the other cold conditions in the initial stage. Additionally, similar results were also found in the research of Ainsalo [24], although he investigated high-pressure propane sprays using a diesel injector.…”