Yoshinobu Yoshihara

A STUDY OF SOLUBLE ORGANIC FRACTIONS IN PARTICULATES EMITTED FROM A HIGH-SPEED DIRECT-INJECTION DIESEL ENGINE

The soluble organic fraction (SOF) of particulates emitted from a high-speed four-cycle DI diesel engine at various loads for commercial diesel fuels and some blended and distillate fuels is studied under steady operating conditions. The fuels examined have various final boiling points and aromatic contents. Emissions of lubricant, fuel fractions, and combustion products in the SOF are evaluated by chemical analysis. Exhaust emission data indicates that the addition of aromatic hydrocarbons to fuel does not cause increases in SOF or in solid fraction, and that heavier components of fuel are responsible for high level of SOF emission at medium load mainly due to the deposition of fuel on the wall of the piston cavity. Flow reactor experiments under atmospheric pressure have been conducted to look at the temperature effect of forming SOF. The results successfully explain the dependence of SOF emission on load and fuel properties. (A) For the covering abstract see IRRD 865952.

Combustion and Emissions Characteristics of a Polypropylene Blended Diesel Fuel in a Direct Injection Compression Engine

The authors investigated the formulation, combustion and emissions of polypropylene (PP)–diesel fuel mixtures in a direct injection diesel engine. The fuel has been obtained by an original technology they developed, in which the low or high density polypropylene (LDPP, HDPP), have been mixed in a nitrogen atmosphere at 200 °C, 10–40% by wt. in diesel fuel. The kinematic viscosity of the polypropylene-diesel fuels was investigated between 25–250 °C and the results showed that viscosity of the plastic mixtures is much higher than that of diesel alone, ranging from 10 cSt to 500 cSt, and depending on the plastic structure, content, and temperature. The TGA and DTA analysis has been conducted to investigate the oxidation and combustion properties of pure PP and polymerdiesel fuels. The results showed that at about 125 °C, the LDPP melts, but does not decompose up 240 °C, when the oxidation starts, and has a peak of heat release at 340–350 °C, and the process is completed at 400 °C. The engine’s injection system used, was a piston-barrel type pump, capable of an injection pressure of 200 bars. The injector had 4 × 0.200 mm nozzles with a conical tip needle. The 25% PP-diesel mixture had a successful ignition in a direct injection 110 mm bore, omega combustion chamber engine. The ignition delay for polypropylene-diesel mixtures was longer by about 0.5 ms (at 1200 rpm), compared with diesel. The heat release showed a different development compared with the reference diesel fuel, the premixed phase being inhibited while a slow diffusion combustion phase fully developed. The maximum combustion pressure has been 83 bars for diesel and decreased by 2 bars for the blended fuel, while the bulk gas maximum temperature (calculated) reached about 2500 K for diesel vs 2600 K for polypropylene mixture. The heat flux calculated by the Annand model has shown lower values for diesel fuel with a maximum of about 2.7 MW/m2 compared with 3.0 MW/m2 for PP blended fuel with similar values for convection flux for both fuels at about 1.57 MW/m2 and a higher radiation flux of about 1.44 MW/m2 for PP fuel versus 1.27 MW/m2 for diesel. The heat lost during the cycle shows low values for the premixed combustion stage and increased values for the diffusion stage for both fuels. The exhaust temperatures have been practically identical for both fuels for all loads, with emissions of NOx, and CO reduced by 40% for the alternative fuel, while the CO2 exhibited almost the same values for both fuels. The smoke emissions decreased by 60–90% for the polypropylene blended fuel depending on the load, The engines’ overall efficiency was slightly lower for PP fuel at low loads compared with diesel combustion but at 100% load both reached 36%. The study showed that the new formulation process proposed by the authors is able to produce a new class of fuels from diesel blended with low density polypropylene, and resulted in hybrid fuels with very promising combustion prospects. The engine investigation proved that 25% PP fuels can be injected and burnt in a diesel engine at a residence time of about 5 ms from the start of injection, and the engine’s nominal power could be reached, with lower emissions than reference diesel fuel.Copyright

A diagnostic bi-zonal combustion model for the study of knock in spark-ignition engines

Abstract A bi-zonal model for the combustion process in spark-ignition engines was developed to provide thermodynamic information, using experimental pressure records. The model was applied to the knock analysis, introducing a reduced kinetic mechanism. The unburned gas temperature in an adiabatically compressed core region is shown to be a good approximation for the reaction temperature. The activation energy of the forward rate of the isomerization reaction was determined for each of seven fuels by comparison with the experiments. It is shown that the activation energy has an almost linear dependence on the research octane number.

A Numerical Prediction Method for the Auto-Ignition Process in a Homogeneous Charge Compression Ignition Engine

An auto-ignition process in a homogeneous charge compression ignition engine has been numerically solved by the Very Large Eddy Simulation (VLES) which integrates a reduced kinetic model for the low temperature oxidationof hydrocarbon fuels. We employ a new method to set the initial turbulent velocity field, reforming the velocity field so that the turbulence dissipation process may fit the results of the K-e model simulation. The phase-averaged quantities of the VLES agree well with those of the K-e model simulation. The VLES exhibits the spatially random appearance of auto-ignition sites, which is similar to experimental observations shown in the reference literature.

Simulation of Artificial Turbulence by the Vortex Method

First, a simple and accurate numerical method is presented to produce velocity fluctuations that are determined by the prescribed physical quantities and qualities of turbulence such as longitudinal and lateral spectra, and integral scales. The fluctuations are obtained by solving a system of nonlinear equations that are derived from the equations of energy spectra and of root mean square of the fluctuations. This method requires as many computer memories and computations as one-dimensional case even for the three dimensional calculations. It is shown that there is a strong resemblance of the simulated velocity fluctuations and experimental data. The energy spectra of these velocity fluctuations are quite accurate with less than 0.01% relative errors to the prescribed spectra. Secondly, these solutions are used to examine the capability of the vortex methods to produce turbulent flows with the prescribed parameters. It is found that although the energy spectra by the vortex method scatter to some extent, they are distributed along the prescribed spectra. It can be said that the vortex methods are able to simulate the target turbulence fairly well. Also it is found that the solutions with the LES model increase and deviate from the target spectrum at the higher frequency regions. This may suggest the nonessentiality of the LES model for the vortex method.Copyright

An investigation of soot- and PAH-formation based on chemical equilibrium.

To explore the formation of polycyclic aromatic hydrocarbons (PAH) and soot during combustion, equilibrium compositions of fuel-rich mixtures at elevated temperatures have been obtained based on thermodynamic considerations. In the calculations, only gaseous intermediates have been included, while solid carbon has been excluded on the assumption that the formation of carbon particles is much slower than other species. It has been shown that major intermediates before sooting are PAH and acetylene. At atmospheric pressure, a maximum PAH concentration appears at about 1400 K, while the acetylene concentration increase with temperatures above 1200 K. A comparison with the experimental results of a heated flow reactor suggests that the present prediction explains the formation of SOF and dry soot during thermal decomposition. Further, a discussion is given of the effects of the C/H ratio and enthalpy of fuel formation on PAH and soot.