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The present study experimentally investigated the performance and emission characteristics of the diesel engine with hydrogen added to the intake air at late diesel-fuel injection timings. The diesel-fuel injection timing and the hydrogen fraction in the intake mixture were varied while the gross heating value per second of diesel fuel and hydrogen was kept constant at a certain value. NO showed minimum at specific hydrogen fraction. The maximum rate of incylinder pressure rise also showed minimum at 10 vol% hydrogen fraction. The indicated thermal efficiency was almost constant or slightly increased with small amount of hydrogen. A combination of hydrogen addition and late diesel-fuel injection timing contributed to low temperature combustion, in which NO decreased without the increase in unburned fuel.

In PCCI diesel engine, the fuel is injected much earlier than the injection timing of conventional diesel engines. Exhaust-emission improvements are attained by the lean-premixed combustion. It is expected that fuel properties influence mixture formation and combustion characteristics. In this research, experiments were carried out using a single-cylinder PCCI diesel engine operating on pure fuels with different volatilities. The injection timing and overall equivalence ratio of the premixed spray were varied. The results showed that the maximum heat release rate was smaller for lower-volatility fuel while ISFC was maintained smaller. So the combustion of a lower-volatility fuel would moderately make progress.

Noise reduction is the needs of the time even for (demanded even from) the outboard motors which are typically used under heavy load and in higher engine speed for an extended period of time. For the sound emitted by an outboard motor, the acoustic impression to human ears largely depends on the high frequency intake noise. The high frequency intake noise is generated by the air flow that passes through the intake pipes at high speed. The test performed with a flow stand bench demonstrated that the sound pressure increment relative to the increasing flow velocity is definitely larger in high frequency band compared with that in low frequency band. Pressure wave form inside the intake pipe was measured relative to the crank angle. The measurement revealed that the high frequency sound is generated in the later part of the intake stroke when the flow velocity within the intake pipe becomes the highest.

The separation of combustion noise and mechanical noise from the total noise of a four-cylinder in-line diesel engine at idling was carried out with high accuracy by changing the fuel injection timing. The mechanical noise, which accounts for the major share at 93%, was then separated into noises from the typical mechanical causes, and the valve train was found to be the major noise source. From analysis of the noise generating mechanism for the valve train, it was clarified that the noise was caused mainly by the gear rattling owing to the variation in the camshaft drive torque.

In a running engine, various impacts are excitation sources for structural vibrations and engine noises. Engine noises are classified, depending on their excitation sources, into the combustion noise, the combustion induced mechanical noise and the mechanical noise. It is difficult to measure such noises separately because some impacts occur closely in time and space. In this paper, a transient noise generation model of an engine was proposed considering vibration and its damping of engine structure. The present model was verified through the single explosion excitation experiment for a stationary engine. Using the noise generation model, the combustion noise was separated from the total noise radiating from a running four-stroke gasoline engine for motorcycles. It was found that the combustion noise had larger power at lower frequencies than higher frequencies. However, its contribution to the total engine noise was relatively small.

Exhaust emission characteristics of direct injection diesel engines under dual-fuel operations with dimethyl ether (DME) were investigated. Two types of DME mixing methods were employed; one is fumigation and the other is binary-fuel injection (BFI). When the DME was used with the fumigation method, low emissions in THC and high emissions in smoke were obtained in comparison with diesel fuel alone. In the BFI method, DME mixing caused a decrease in the NO emissions without increasing the THC emissions, but some amount of smoke was exhausted at high load. Knocking cycles occurred for over 60 % DME fraction.

In a structure, the noise source does not always coincide with the origin of excitation. Vibrational energy is transmitted in the structure and noise is radiated from the surface. For noise and vibration control in beam or shell structures, it is important to clearly identify the excitation sources and vibrational energy transmission characteristics. In this paper, measurement of transient vibrational power flow in a car door excited by impact using the envelope vibration Intensity technique is described. Vibrational power flow caused by flexural vibration in the car door panel is measured with the three channel method. The vibrational power flow is expressed with vibration intensity vectors at each measuring point. Instantaneous distributions of measured vibration intensity vectors in the car door panel are shown in this paper. Temporal and spatial variations of the vibrational power flow are discussed.

The interaction phenomena of the internal flow and the acoustic resonance noise in expansion cavity type mufflers was investigated. The generation conditions of this phenomena and the predominance of acoustic resonance noise were examined. According to the distribution of fluctuating velocity generated in the cavity, the location where the vortexes were generated in the cavity and the amplifying process of the vortex rings were clarified.

Vibration intensity measurement using a three channel method is proposed as a means for the identification of the impact sources in a machine structure. The envelope intensity technique is also employed to catch the transient feature of the intensity vectors. The application limits of the three channel method and the intensity pick-up are discussed. Vibration intensity measurement is applied to an engine structure in order to clarify the direction of the vibration energy flow caused by combust ion impact.

This paper describes the results of using vibration intensity measurement to identify the source of impact in an engine structure. To determine the signal processing conditions of the responses, the vibration energy flow delivered by an impulsive force to a rectanguler plate was investigated while undergoing background vibration. The direction of the vibration power flow was measured at certain points in stationary engine walls excited by an impulse hammer. This measurement was also applied to a running engine structure, and the results were shown for the valve-seating impact of a single cylinder diesel engine as an example.

This paper describes an attempt to clarify the characteristics of combustion noise generation of the engine structure. The transmission-radiation coefficient of combustion noise is proposed as a conversion ratio of the combustion noise power from the gas vibration power affecting the inner surface of the combustion chamber These experiments were carried out both with a stationary engine excited by a single explosion and an operating engine. From these results, the frequency characteristics of the combustion noise generated by each engine wall and the vibration response of each transmission path are discussed.

In the present work, an attempt was made to predict engine noise from the shape of the burning rate curve. Thus, the influence of the shape of the burning rate curve on engine noise, especially on combustion noise was studied in detail and clarification of the relationship was successfully made. At first, an approximation of burning rate curve using a function was attempted. And in second, the transfer rate from cylinder pressure to combustion noise was obtained. Then, the relation between the deciding parameters of burning rate curve and noise and performance of engine were studied.