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In order to deal with upcoming and ever-more stringent diesel engine exhaust emissions limits, efficiency requirements, and after-treatment technology, further technology advancement has been required of the fuel injection system. In this research, CRS with the capability of varying the injection rate shape installed on a single cylinder and a multi-cylinder test engine, and tests were carried out. Results showed that with control of the injection rate shape, it became possible to control combustion and improve the NOx-fuel consumption and NOx-PM trade offs by offering the ability to optimize the injection rate. This leads one to believe that injection rate shape control is an essential function for future fuel injection systems.

The lean NOx trap (LNT) has been proposed as a NOx after-treatment device for diesel engines. In order to successfully apply a LNT to diesel engines, it has thus far been necessary for the LNT to have intermittent rich operation (so-called rich spike, RS), and the stored NOx is purged and reduced by RS to maintain NOx conversion performance. However, since RS tends to increase fuel consumption, optimized RS control is necessary to keep the fuel consumption increase to a minimum. In order to do that, a suitable LNT control system is necessary, like one that has the functionality to accurately estimate the amount of stored NOx, and indicate the proper RS timing according to this value. In this research a model-based control method was adopted to accurately estimate the amount of stored NOx present in the LNT. The LNT parameters were characterized by polynomial fits and modeled. Moreover, using a NOx sensor mounted downstream of the LNT, an adaptive estimation method was adopted.

Injection rate control is an important capability of the ideal injection system of the future. However, in a conventional Common-Rail System (CRS) the injection pressure is constant throughout the injection period, resulting in a nearly rectangular injection rate shape and offering no control of the injection rate. Thus, in order to realize injection rate control with a CRS, a "Next- generation Common-Rail System (NCRS)" was conceptualized, designed, and fabricated. The NCRS has two common rails, for low- and high-pressure fuel, and switches the fuel pressure supplied to the injector from the low- to the high- pressure rail during the injection period, resulting in control over the injection rate shape. The effects of injection rate shape on exhaust emissions and fuel consumption were investigated by applying this NCRS to a single- cylinder research engine.

Injection rate shape control is one feature of a diesel fuel injection system that is strongly desired at this time. However, in the conventional Common Rail System (CRS), it is difficult to control the injection rate because the injection pressure is constant during the injection period, resulting in a nearly rectangular rate shape. Thus, in order to achieve injection rate control in a CRS, a Next-generation Common Rail System (NCRS) was designed and the prototype system was fabricated. With two common rails, one for low pressure fuel, and the other for high pressure fuel, the NCRS achieves injection rate shape control by controlling the fuel injector supply pressure, from the two rails. The NCRS can achieve a clear “boot” shaped injection rate, and injection rig tests confirmed that the shape could be flexibly controlled via several control parameters.

In this study three EGR methods were applied to a 12 liter turbocharged and intercooled Dl diesel engine, and the exhaust emission and fuel consumption characteristics were compared. One method is the Low Pressure Route system, in which the EGR is taken from down stream of the turbine to the compressor entrance. The other two systems are variations of the High Pressure Route system, in which the EGR is taken from the exhaust manifold to the intake manifold. One of the two High Pressure Route EGR systems is with back pressure valve located at downstream of the turbine and the other uses a variable geometry(VG) turbocharger. It was found that the High Pressure Route EGR system using VG turbocharger was the most effective and practical. With this method the EGR area could be enlarged and NOx reduced by 22% without increase in smoke or fuel consumption while maintaining an adequate excess air ratio.

In this study a new water injection system was applied to an 11 liter naturally aspirated DI diesel engine in order to reduce exhaust emissions. In this system, the water and fuel were arranged in the injection nozzle during the time between injections as fuel, water and then fuel. The fuel and water were then injected into the cylinder in that order. The tests were conducted at several engine operating conditions from the Japanese 13 mode test cycle to clarify effects of water injection on exhaust emissions and fuel consumption. The results showed that NOx reduction was directly proportional to the relative amount of water injection, regardless of engine speed and load. By using the optimal relative amount of water injection at each engine operating condition, total NOx and particulate matter (PM) in the Japanese 13 mode test cycle were reduced by 50% and 25%, respectively, without a fuel consumption penalty.

In the diesel engine industry, the growing trends are toward wider use of electronically controlled high pressure fuel injection equipment to provide better engine performance, while conforming to the stringent exhaust emission standards. Although there have been some recent announcements of a diesel engine that applies an electronically controlled common rail type fuel injection system, there is little literature published about any attempt to reduce both exhaust emissions and noise and to improve engine performance by varying injection pressure and injection timing independently and introducing pilot injection in combination. This paper describes the details of a study made on the parameters associated with injection timing, injection pressure and pilot injection and the procedures for their optimization, with an electronically controlled common rail type fuel injection system installed in an in-line 6-cylinder 6.9 liter turbocharged and intercooled DI diesel engine.

In order to reduce exhaust emission and combustion noise and to improve fuel consumption, the effects of the combustion system parameters of a diesel engine, such as injection pressure, injection nozzle hole diameter, swirl ratio, and EGR rate on exhaust emissions, combustion noise and fuel consumption are investigated and described in detail by analyzing rate of heat release, needle valve lift and injection pressure. Based on these results, reduction of exhaust emission and combustion noise and improvement of fuel consumption are described in the latter part of this paper. These results are shown as follows. The smaller nozzle hole diameter is effective for reducing smoke and PM, and by optimizing the injection timing and swirl ratio, NOx can also be reduced. In addition to the above, by applying EGR and higher injection pressure it is possible to improve the fuel consumption with the remaining low NOx and PM.