Diesel Spray Characterization at Ultra-High Injection Pressure of DENSO 250 MPa Common Rail Fuel Injection System

High fuel injection pressure has been regarded as a key controlling factor for internal combustion engines to achieve good combustion performance with reduced emissions and improved fuel efficiency. For common-rail injection system (CRS) used in advanced diesel engines, fuel injection pressure can often be raised to beyond 200 MPa. Although characteristics of diesel spray has been thoroughly studied, little work has been done at ultra-high injection pressures. In this work, the characteristics of CRS diesel spray under ultra-high injection pressure up to 250 MPa was investigated. The experiments were conducted in an optically accessible high-pressure and high-temperature constant volume chamber. The injection pressure varied from 50 MPa to up to 250 MPa. Both non-evaporating condition and evaporating condition were studied. A single-hole injector was specially designed for this investigation. High-speed Mie-scattering imaging and Schlieren imaging were used to capture the global structure of the liquid and vapor sprays. In addition, high-speed microscopic back-lit imaging was used to obtain detailed information of sprays near the nozzle. Results show that, the increase of injection pressure from 50 MPa to 250 MPa decreases the injection response time and cut time by 58% and 49% respectively. A correlation of injection rate and the velocity of initial spray was observed. The initial spray experiences a quick accelerating to its maximum velocity, then quickly slows down, and higher injection pressure results in shorter accelerating time and higher maximum velocity. In addition, spray liquid penetration increases as injection pressure increases under non-evaporating conditions. However, under evaporating conditions, the increase of injection pressure from 50 MPa to 250 MPa results in about 15% decrease of liquid penetration but increase of vapor penetration.