Experimental study on the gas jet characteristics of a diesel-piloted direct-injection natural gas engine

The natural gas (NG) jet characteristics of NG/diesel dual-fuel injection under different NG injection pressures and dual-fuel injection intervals were studied in a constant volume chamber. The schlieren images showed that the development of NG jet was restricted in both axial and radial directions by diesel spray under dual-fuel injection conditions. Consistently, dual-fuel injection reduced NG jet tip penetration, NG jet cone angle and NG jet volume, yet increased average fuel-air equivalent ratio, compared to NG single-fuel injection. The increase of NG injection pressure from 3 MPa to 5 MPa enhanced NG jet tip penetration and NG jet volume, yet decreased jet cone angle under both single-fuel and dual-fuel injection conditions. The negative effects of diesel spray on NG jet became gradually reduced with the increase of injection interval. When the injection interval was longer than 1.5 ms, NG jet characteristics were close to those under single-fuel conditions.