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Modeling of shock absorbers is often used to either study and/or tune its parameters or to calculate the damping force as an input to the vehicle oscillation simulation. Shock absorber damping is accomplished by the oil resistance to flow-through restrictions. Due to their complex design and flow paths, one of the major difficulties is to determine the flow discharge coefficient and actual geometric flow area at these restrictions. This paper proposes an approach where the effective flow area (product of discharge coefficient and geometric flow area) is calculated based on the results of a simple vehicle oscillation test, combined with a shock absorber model. Governing equations are solved numerically resulting in useful dependence of the effective flow area at the absorber restrictions and the pressure differential between the compression and rebound chambers. The Methodology is described in detail.

The benefits of direct cylinder fuel injection to the fuel economy and exhaust emissions of small spark ignited two-stroke engines is well known. The selection of a commercially viable fuel injection solution continues to receive evaluation and scrutiny by the engine manufacturers. This paper describes the development and demonstration of an EDFI solution which is applicable to low cost and high production volume engines in several industries. The system is based on the “accumulator” fuel injection operating principle, which involves pressurizing fuel within an injection nozzle and subsequently releasing the pressurized fuel into the combustion chamber on command. This concept provides very short injection duration throughout the dynamic operating range of the engine as well as high injection frequency capability.

Natural gas is a low cost, abundant and clean burning fuel. Current internal combustion engines can be readily adapted to use natural gas fuel either in conjunction with conventional liquid fuels or as dedicated systems. Use of modern electronic controls allows consideration of new engine management strategies that are not practical or even possible with mechanical systems. The preferred approach is pre-mixed lean burn with cylinder-by-cylinder fuel injection and full time control of optimized air/fuel ratio and ignition.

Dual-fuel pilot ignited natural gas engines have several intrinsic advantages relative to spark ignited; mainly higher thermal efficiency and lower conversion costs. The major drawback is associated with light loads. This paper discusses objectives, approaches, methods and results of the development of strategies which overcome the drawbacks and enhance the advantages. Development of a pilot fuel injection system, having a delivery of only 1 mm3 at a duration of 0.6 ms, was described in a previous paper. This paper concentrates on the results of strategies to reduce unburned methane in the exhaust and to increase the substitution of gas at light loads through skip-fire, by-passing boost air and exhaust gas recirculation techniques. Engine tests proved that with these strategies, diesel fuel replacement of more than 95% over the entire engine operating map, including idle, can be achieved and current and anticipated future emission standards satisfied.

The paper discusses objectives, approaches and results of the development of a pilot fuel injection system (FIS) for a dedicated, compression ignition, high-speed, heavy duty natural gas/diesel engine. The performance of the pilot FIS is crucial for the success of a dual fuel concept. The Servojet electro-hydraulic, accumulator type fuel system was chosen for the pilot fuel injection. An alternative pilot FIS based on the “water hammer” (WH) effect was also considered. The modifications to a stock 17 min injector is described. Three different types of pilot injector nozzle were investigated: standard Valve Covered Orifice (VCO), modified minisac and new designed, unthrottled pintle. Preliminary results from engine tests proved that the optimum pilot fuel quantity is the minimum quantity. Based on that finding, the pilot FIS design was further optimized.