An ultrahigh injection pressure, common rail fuel injection system was designed, fabricated, and evaluated. The result was a system suitable for high-power density diesel engine applications. The main advantages of the concept are a very short injection duration capability, high injection pressure independent of engine speed, a simplified electronic control valve, and good packaging flexibility.Two prototype injectors were developed. Tests were performed on an injector flow bench and in a single cylinder research engine. The first prototype delivered 320 mm3 within 2.5 milliseconds with a 2600 bar peak injection pressure. A conventional minisac nozzle was used. The second prototype employed a specially designed pintle nozzle producing a near-zero cone angle liquid jet impinging on a 9-mm cylindrical target centered on the piston bowl crown (OSKA-S system). The second prototype had the capability to deliver 316mm3 in 0.97ms.A one-dimensional fuel injection simulation code was used to enhance the injector design and to provide the CFD code (KIVA) with injection-related inputs. The three-dimensional KIVA code was used to predict in-cylinder characteristics, helping to explain the experimental results and to suggest system design improvements. Several interesting findings are reported regarding the relationship between the injection rate shape, the injection duration, and the combustion chamber geometry. A new model was developed to capture relevant phenomena during liquid jet impingement on the piston target, subsequent film propagation, and fuel atomization for modeling of the OSKA-S system. The KIVA predictions helped explain the high soot emissions and the long combustion duration obtained during the OSKA-S engine testing. Directions for improvements in engine performance are outlined.Compared with a baseline, modern cam-actuated electronic fuel injection system, the engine test results with the new injection system showed improved engine thermal efficiency and lower exhaust gas temperatures, at lower engine speeds. Since engine structural limits were not exceeded, these results present a potential for engine power density increases.