NH3 combustion using three-layer stratified fuel injection for a large two-stroke marine engine: Experimental verification of the concept

Abstract

A unique liquid NH3 spray combustion concept for a compression ignition engine, which applies a "three-layer stratified fuel injection comprising a supporting fuel / liquid NH3 / supporting fuel (i.e., NH3 stratified injection)” concept, in which the liquid NH3 is sandwiched by the supporting fuels, is proposed for a large two-stroke marine engine. The supporting fuel is a liquid fuel which can be ignited and burnt easily, such as marine gas oil, marine diesel oil, biodiesel oil and synthetic diesel oil produced from renewable energies. The three layers were injected sequentially from a single nozzle, and a three-layered spray was formed. To verify the combustion concept, a constant volume combustion chamber and a stratified fuel injection system were developed to simulate combustion in the cylinder of a large two-stroke engine. We then confirmed that the stratified fuel injection system can very nearly realize a two- or three-layer spray, by measuring the energy injection rate during one injection period. In the experiments, the heat release rates and combustion gas compositions for the NH3 stratified injection were evaluated. From the experimental results, and using the combustion concept, we found that the fuel is ignited and burns up the NH3 in the NH3 stratified injection; it also suppresses N2O production via the combustion of the supporting fuel in the third layer. Consequently, it was found that the combustion concept is effective for liquid NH3 spray diffusion combustion in large two-stroke marine engines.