Takao Karasawa

A study of the combustion and emission characteristics of compressed-natural-gas direct-injection stratified combustion using a rapid-compression-machine

The objective of the present study is to determine the characteristics of combustion and emissions of compressed-natural-gas (CNG) direct-injection combustion using a rapid-compression-machine which has a compression ratio of 10 and a disc-shaped combustion chamber. Combustion and emission characteristics are compared for three types of fuel injection (single side, parallel side and opposed side injection) and a homogeneous mixture. The results show that with fuel injection, the fuel could be burned up to an equivalence ratio φ of 0.2 with sufficiently high combustion efficiency except for the case of φ = 1.0, while with a homogeneous mixture, the lean burn limit was only φ = 0.6 with poor combustion producing higher unburned CH4 By adjusting the location of the spark plug and fuel injectors, the combustion limit was extended to φ = 0.02. The Combustion efficiency of the injection modes is over 0.95 except for φ = 1.0 and φ < 0.06 which gave a lower combustion efficiency. Incomplete combustion in the stratified rich zone reduced the combustion efficiency at large values of φ, and possible occurrence of bulk quenching resulted in the lower combustion efficiency for very lean mixtures. Combustion efficiency for the homogeneous mixture decreases greatly with leaner mixtures, which is probably due to the thicker quenching layer near the wall. Combustion duration with fuel injection was insensitive to φ and was much shorter than for the homogeneous mixture. It was also shown that the number and location of the injectors and the injection rate had little influence on the combustion and the exhaust emissions including NOx. The pressure rise due to combustion in the case of fuel injection is higher compared to that of homogeneous mixture combustion due to the lower heat loss to the combustion chamber walls resulting from a short combustion duration. Thus it is shown that stratified-combustion with extremely lean burn capability can be realized with CNG direct injection.

Performance and emission characteristics of a diesel engine fueled with coconut oil–diesel fuel blend

Abstract The objective of the present study is to reveal the effects of pure coconut oil and coconut oil–diesel fuel blends on the performance and emissions of a direct injection diesel engine. Operation of the test engine with pure coconut oil and coconut oil–diesel fuel blends for a wide range of engine load conditions was shown to be successful even without engine modifications. It was also shown that increasing the amount of coconut oil in the coconut oil–diesel fuel blend resulted in lower smoke and NO x emissions. However, this resulted in an increase in the BSFC. This was attributed to the lower heating value of neat coconut oil fuel compared to diesel fuel.

The effect of coconut oil and diesel fuel blends on diesel engine performance and exhaust emissions

The effect of a coconut oil as diesel fuel alternatives or as direct fuel blends are investigated using a single-cylinder, direct-injection diesel engine. The spray characteristics in terms of the mean droplet diameter of these fuels were measured with a phase Doppler Anemometer. Operation of the test engine with the pure coconut oil and coconut oil–diesel fuel blends for a wide range of engine operating conditions was shown to be successful even without any engine modification. Results show that neat coconut oil fuels gave lower smoke and NOx emissions.

Effect of exhaust gas recirculation on diesel knock intensity and its mechanism

Abstract This paper presents an experimental study of the effect of exhaust gas recirculation (EGR) on diesel knock intensity, which is defined and discussed. In a previous paper, it was reported that particulate emission can be decreased by applying EGR under certain operating conditions; and the possible mechanism of the effect of EGR was presented. In the present study, the effect of EGR on diesel knock is examined under a variety of operating conditions. Diesel knock intensity is decreased considerably by EGR under the same operating conditions as when the particulate emission is decreased. A quantitative relationship between the diesel knock intensity and the maximum rate of cylinder pressure rise is obtained. The effect of EGR on diesel knock intensity is determined by both the chemical reaction rate of the initial premixed combustion (spontaneous ignition) and the fuel mass fraction prepared and burned in this stage. This is verified by measuring the ignition lag and classifying it into chemical and physical lags by a statistical technique presented by S. Kumagai.

Effect of Early-Closing of Intake-Valve on the Engine Performance in a Spark-Ignition Engine

In this paper we present the first stage of a study on the effect of early-closing of intake-valve on the engine performance in a spark-ignition engine. A four-valve single-cylinder engine was used with several values of expansion ratio and a half early-closing intake cam. The half early closing leads to almost a half of the volumetric efficiency and the BMEP for all cases of the expansion ratio. It can realize an improvement of about 7% in thermal efficiency under WOT, and about 4% under partial load of BMEP=0.2 MPa. These beneficial results are considered to be mainly caused by the effect of the more-expansion. The ratio of expansion to compression ratios was estimated to be around. 1.4 on the basis of motoring pressure analyses. Under the early-closing condition, an increase in the residual gas fraction was suggested and verified by a heat release analysis using a two-zone combustion model.

Failure of Spray Droplets to Impact the Cylindrical Sampler in the Iipmersion Sampling Technique

The immersion sampling technique with a cylindrical rotary shutter is quite popular in measuring spray droplet sizes. However some problems with this technique remain unsettled. In this paper the extent to which droplets fail to impact the cylindrical rotary shutter is experimentally investigated. Experiments have been carried out using a steady water jet from a 0.2 mm hole nozzle varing the diameter of the cylindrical shutter from 22.5 mm to infinity (flat plate) and the sampling distance from 800 mm to 2, 300 mm.From the results obtained the following can be concluded:(1) Contrary to expectation, failure of droplets to impact is fairly rare.(2) Though failure to impact increases with an increase in shutter diameter, the rate of increase is very small after the shutter diameter exceeds about 30 mm.(3) Since failure to impact occurs over the whole range of droplet size, arithmetic and Sauter mean diameter and size distribution are not affected significantly by the existence of the rotary shutter.