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This paper describes the experimental studies of turbocharged and intercooled diesel engines with particular emphasis on combustion characteristics following increase of boost pressure. Through these studies, it has become possible to determine the optimum air quantity for minimizing fuel consumption at each engine speed range under the restrictive conditions of NOx emission, exhaust smoke and maximum cylinder pressure. Discussed also is the lack of air quantity in the low engine speed range of high-boost turbocharged diesel engines. Various turbocharging systems to improve air quantity in this speed range are introduced herein. Practically the engine performance of conventional turbocharging, waste gate control turbocharging and variable geometry turbocharging are discussed from the viewpoint of torque recovery in the low engine speed range.

Diesel particulate trap systems are one of the effective means for the control of particulate emission from diesel vehicles. Hino has been researching and developing various diesel particulate trap systems for city buses. This paper describes two of the systems. One uses a wall flow filter equipped with an electric heater and a sensing device for particulate loading for the purpose of filter regeneration. Another makes use of a special filter named “Cross Flow Filter” with an epoch-making regeneration method called “Reverse Jet Cleaning”, by which it becomes possible to separate the part for particulate burning from the filter. Both systems roughly have come to satisfy the functions of trap systems for city buses, but their durability and reliability for city buses are not yet sufficient.

Future emission standards for heavy duty diesel engines will require extensive development using an integrated approach. This paper describes the latest results from HINO heavy duty diesel engine combustion research program. Improvement of the NOx/particulate/fuel economy trade off requires fuel injection equipment of Pump Line Nozzle (PLN) System and unit injector with high pressure capability, injection rate control and timing control, and a combustion system matched with high pressure injection. Combustion characteristics (ignition delay, combustion period, heat release curve), fuel consumption, particulate, and exhaust gas emission of each injection system are compared and discussed. The unit injector system has an advantage of lower particulate level, especially dry soot, than the Pump Line Nozzle system. The potential for further improvement through engine modification and aftertreatment is also discussed.

For the 1990's diesel engines, particulate control has been an important problem. The purpose of this paper is to discuss emission control needs for heavy duty diesel truck engines for the 1990's. This paper will focus on the factors such as fuel injection pressure and fuel properties which most affect particulate emission. The characteristics of diesel spray in the atmosphere and also actual combustion of a turbocharged and charge-cooled H.D. D.I diesel engine were studied as a function of injection pressure ranging from 50 to 150 MPa. Experimental results show that high pressure injection improves the atomization and air entrainment. Though Bosch smoke level, fuel consumption and combustion period decreased with the rise of injection pressure, particulate emission in EPA transient test cycle did not decrease dut to an increase of SOF.

In heavy duty vehicles, a higher boost and/or smaller sized diesel engine is quite effective in achieving fuel economy. However, this causes an increase of pumping loss due to increased intake air and exhaust gas flow of the engine at high load and high speed conditions. It also causes a relatively poorer torque at low speed conditions due to a lack of boosted air. The authors investigated the pumping loss and volumetric efficiency of a high boosted turbocharged diesel engine and analyzed the effects of the turbocharger, inertia charging and the valve opening areas. An optimization of small geometry turbine housing was obtained for the improvement of both low speed torque and fuel economy. The effects of inertia charging were ascertained from the relation between engine valve timing and the amplitude and phase of intake air pulsation. Increasing the intake and exhaust valve opening area improved fuel consumption by reducing pumping loss.