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Technical Paper

BSFC Improvement and NOx Reduction by Sequential Turbo System in a Heavy Duty Diesel Engine

Reduction of exhaust emissions and BSFC has been studied using a high boost, a wide range and high-rate EGR in a Super Clean Diesel, six-cylinder heavy duty engine. In the previous single-turbocharging system, the turbocharger was selected to yield maximum torque and power. The selected turbocharger was designed for high boosting, with maximum pressure of about twice that of the current one, using a titanium compressor. However, an important issue arose in this system: avoidance of high boosting at low engine speed. A sequential and series turbo system was proposed to improve the torque at low engine speeds. This turbo system has two turbochargers of different sizes with variable geometry turbines. At low engine speed, the small turbocharger performs most of the work. At medium engine speed, the small turbocharger and large turbocharger mainly work in series.
Technical Paper

The Effect of Knock on Heat Loss in Homogeneous Charge Compression Ignition Engines

One of the problems in HCCI combustion is a knocking in higher load conditions. It governs the high load limit, and it is suggested that the knock increases heat loss[1], because it breaks the thermal boundary layer. But it is not clear how much knock affects on heat loss in the HCCI combustion in various conditions, such as ignition timing and load. The motivation of this study is to clarify the ratio of heat loss caused by knock in HCCI engines. The heat loss from zero-dimensional calculations with modified heat transfer coefficient, which is considering the effect of knock by adding a term of cylinder pressure rising rate dp/dt, agreed well with the results from the thermodynamic analysis in various conditions. And the results show that it is possible to avoid heat loss by knock by controlling the ignition timing at appropriate timing after T.D.C. and it will be possible to expand the load range if knock can be avoided.
Technical Paper

Fuel Consumption Improvement and Operation Range Expansion in HCCI by Direct Water Injection

HCCI (Homogeneous Charge Compression Ignition) combustion results in very low NOx emissions, however, it is not without problems. One of them is that the heavy load operation range is limited by knock, due to an exceptionally high heat release rate. Knock increases the heat loss to the cylinder walls and piston, reducing thermal efficiency. To help solve these problems, direct (in-cylinder) water injection has been suggested to lower the local temperatures that seem to cause knock in HCCI. Water injection was adapted in an HCCI engine fueled with DME and Propane. Results showed that the indicated thermal efficiency was improved by about 2% (λ = 3.0, NA), and the operation range was expanded from 460kPa to 700kPa (NA) maintaining a low NOx level.
Technical Paper

Characteristics of Fuel Sprays from Specially Shaped and Impinging Flow Nozzles

Two ways to attain low emission diesel combustion, which are capable of meeting future regulations, are the so-called two-stage “rich and lean” combustion and ‘lean” diesel combustion. To actually achieve these types of combustion, homogeneous lean air-fuel mixture formation is very important In this study, two methods of producing a desirable air-fuel mixture axe investigated experimentally by observing fuel sprays from several unique injection nozzles in a high-pressure vessel. One was a slit shaped hole nozzle, which might result in increased air entrainment into the spray because of the larger surface area. The other was impinging flow nozzle, which generated a more homogeneous mixture by its high turbulence. It was observed that with the slit shaped hole nozzle, the cross-sectional shape of the spray was unexpectedly circular, which was attributed to a greater dispersion of the spray perpendicular to the lengthwise slit axis.
Technical Paper

Effects of Multi-Hole Nozzle with Throttle Construction on Diesel Combustion and Emissions with High-Pressure Fuel Injection

The effects of a multi-hole nozzle with throttle construction (NTC) on combustion and emissions were investigated at high pressure fuel injection conditions. The throttle area was larger than the total injector hole area, therefore its fuel flow quantity was about the same as the standard nozzle under steady flow conditions. But the initial fuel injection rate was lower under unsteady flow conditions and smoke emissions were improved with the NTC. It is postulated that these effects were due to fuel flow turbulence inside the nozzle during the time of needle valve lift.
Technical Paper

An Analysis on Heat Loss of a Heavy-Duty Diesel Engine by Wall-Impinged Spray Flame Observation

Impingement of a spray flame on the periphery of the piston cavity strongly affects heat loss to the wall. The heat release rate history is also closely correlated with the indicated thermal efficiency. For further thermal efficiency improvement, it is thus necessary to understand such phenomena in state of the art diesel engines, by observation of the actual behavior of an impinging spray flame and measurement of the local temperature and flow velocity. A top-view optically accessible engine system, for which flame impingement to the cavity wall can be observed from the top (vertically), was equipped with a high speed digital camera for direct observation. Once the flame impinged on the wall, flame tip temperature decreased roughly 100K, compared to the temperature before impingement.
Technical Paper

Enhancing Peak Firing Pressure Limit for Achieving Better Brake Thermal Efficiency of a Diesel Engine

An increased cycle expansion ratio is beneficial from a thermodynamic viewpoint to increase the engine efficiency. In this study, the target compression ratio and corresponding thermodynamic cycle layout were investigated by means of a new ideal combustion cycle. To model the experimental pressure traces, the combustion was divided into three parts; constant volume combustion, early expansion combustion and late combustion. This study discussed optimal parameter values for compression ignition combustion under PFP constraints. These parameters included compression ratio, pressure ratios as well as cut-off ratios. Furthermore, this study experimentally investigated the limitation of thermal efficiency and the variation of energy losses under different geometric compression ratios, boosting pressure and degree of constant volume combustion. These experiments utilized a supercharged single-cylinder heavy duty diesel engine with PFP-capability of up to 30 MPa.