Diffusion Combustion Phase Research Articles

Engine performance and emission characteristics of a compression ignition engine fuelled with diesel/dimethoxymethane blends

The performance and emissions of a compression ignition engine fuelled with diesel/dimethoxymethane (DMM) blends were studied. The results showed that the engine's thermal efficiency increased and the diesel equivalent brake specific fuel consumption (b.s.f.c.) decreased as the oxygen mass fraction (or DMM mass fraction) of the diesel/DMM blends increased. This change in the diesel/DMM blends was caused by an increased fraction of the premixed combustion phase, an oxygen enrichment, and an improvement in the diffusive combustion phase. A remarkable reduction in the exhaust CO and smoke can be achieved when operating on the diesel/DMM blend. Flat NO x/smoke and thermal efficiency/smoke curves are presented when operating on the diesel/DMM fuel blends, and a simultaneous reduction in both NO x and smoke can be realized at large DMM addition. Thermal efficiency and NO x give the highest value at 2 per cent oxygen mass fraction (or 5 per cent DMM volume fraction) for the combustion of diesel/DMM blends.

Performance and Emissions of a Compression Ignition Engine Fueled with Diesel/Oxygenate Blends for Various Fuel Delivery Advance Angles

Oxygenated blends were prepared by adding methanol and solvent to diesel fuel, and engine performance and emissions of the oxygenated blends under various fuel delivery advance angles were conducted in a compression ignition engine. The results showed that the engine thermal efficiency increased and the diesel-equivalent brake specific fuel consumption decreased as the fuel delivery advance angle for the oxygenated blends increased, and the behavior had a tendency to be more obvious at high engine speed. The NOx concentration in the oxygenated blends increased as the fuel delivery advance angle increased. For a specific fuel delivery advance angle, the NOx concentration increased as the oxygenate mass fraction in the fuel blends increased, whereas a large addition of oxygenates in the diesel fuel reduced the NOx concentration. The addition of oxygenate in the diesel fuel had a strong influence on the NOx concentration at high engine load, whereas it had little influence at low engine load. The CO content decreased as the fuel delivery advance angle at high engine load became retarded, whereas at middle and low loads, the CO concentration varied little with variation of the fuel delivery advance angle but presented a low value for the diesel/oxygenate blends. The fuel delivery advance angle had little influence on the exhaust hydrocarbon (HC) content for the diesel/oxygenate blends. The amount of smoke can be decreased remarkably by the addition of oxygenate in diesel fuel at the setting of various fuel delivery advance angles. The amount of smoke decreased as the fuel delivery advance angles for both diesel fuel and diesel/oxygenate blends increased; this phenomenon would be due to the increase in the fraction of fuel burned in the premixed burning phase and the decrease in the fraction of fuel burned in diffusive combustion phase, as well as the improvement of the diffusive combustion in the presence of oxygenated blends. The study also showed that a flat NOx/smoke trade-off curve existed when the oxygenated blends were used.

Partially premixed charge compression ignition engine with on-board [formula omitted] production by exhaust gas fuel reforming of diesel and biodiesel

The application of the exhaust gas fuel reforming process in diesel engines has been studied experimentally as a way to assist the premixed charge compression ignition operation by substituting part of the main fuel with hydrogen-rich gas. The technique involves the injection of hydrocarbon fuel into a catalytic reformer fitted into the exhaust gas recirculation (EGR) system, so that the produced gas mixture is fed back to the engine as reformed EGR (REGR). First, experiments with simulated REGR were conducted with diesel as well as biodiesel as the main engine fuel. Then, experiments with the product gas of a monolith reformer were carried out. In both cases, REGR resulted in a higher premixed combustion rate and reduction of the diffusion combustion phase. The potential of the technique in terms of achieving reduction of smoke and NO x emissions and improved fuel economy has been shown and discussed in the paper.

The modification of the fuel injection rate in heavy-duty diesel engines: Part 2: Effects on combustion

An experimental study has been performed on the effects of injection rate shaping on the combustion process and exhaust emissions of a direct-injection diesel engine. Boot-type injections were generated by means of a modified pump-line-nozzle system, which is able to modulate the instantaneous fuel injection rate. The influence of different values of boot length and boot pressure has been evaluated by analysing the apparent rate of heat release and flame temperatures. Engine operating conditions at different rotating speed and injected fuel mass were considered in order to assess their effect on the injection rate shape. Results show how all the changes in the injection rate agree with changes in the diffusion combustion phase. Medium-load conditions presented larger increases in the dry soot emissions since the boot was longer and it was produced at lower pressure. Changes in engine speed at high load did not show major changes in the combustion evolution. Longer boots produced high soot emissions probably due to less efficient mixing conditions.

Engine performance and emissions of a compression ignition engine operating on the diesel-methanol blends

A stabilized diesel-methanol blend was realized and a study on the performance and emissions of the diesel-methanol blend was carried out in a compression ignition engine. The study showed that the engine thermal efficiency increases and the diesel equivalent b.s.f.c. decreases with increase in the oxygen mass fraction (or methanol mass fraction) of the diesel-methanol blends due to an increased fraction of premixed combustion phase, oxygen enrichment and improvement in the diffusive combustion phase. Further increase in the fuel delivery advance angle will achieve a better engine thermal efficiency when the diesel engine is operated using the diesel-methanol fuel blends. A marked reduction in the exhaust CO and smoke can be achieved when operating with the diesel-methanol blend. There is not a large variation in the exhaust hydrocarbon with the addition of methanol in diesel fuel. NOx increases with increase in the mass of methanol added; methanol addition to diesel fuel was found to have a strong influence on the NOx concentration at high engine loads rather than at low engine loads, and a flat NOx-smoke trade-offcurve exists when operating with the diesel-methanol fuel blends.

Development of a zero-dimensional Diesel combustion model: Part 2: Analysis of the transient initial and final diffusion combustion phases

The objective of this work is the development of a zero-dimensional Diesel combustion model. After the development of a model based on the apparent combustion time for the central phase of the quasi-steady Diesel diffusion combustion [Appl. Therm. Eng. 23 (2003)], this second part describes the work of generalization of the model for the final and initial transient phases of the diffusion combustion. For this purpose, those transient phases are analyzed mainly on the basis of the results of CFD calculations for pulsed gas jets. The generalization for the final transient diffusion combustion phase is based on the analysis of the evolution of the turbulent effective viscosity dissipation at the end of the injection process. For the initial transient diffusion combustion phase the work is based on the analysis of the air/fuel mixture at the beginning of the injection process. The result is a zero-dimensional model capable of predicting the diffusion combustion in a Diesel engine. The validation of the proposed model has been performed on both a high speed Diesel engine and a heavy duty Diesel engine.

Ignition timing control of homogeneous charge compression ignition engines by pulsed flame jets

In diesel engines, most of the fuel is burned in a diffusion combustion phase, which inherently leads to the formation of excessive amounts of soot and NOx emissions. In order to decrease soot and NOx emissions simultaneously, the concept of a lean homogeneous charge compression ignition engine has been proposed. The onset of the combustion of the engine depends on the autoignition of the fuel, so it is quite difficult to control the ignition timing. On the other hand, it has been revealed that Pulsed Flame Jet (PFJ) has a great potential to enhance ignition reliability and burning rate in lean mixtures. In this article, autoignition characteristics of n -butane/air mixtures in a rapid compression machine (RCM) were shown first. The appearance of low temperature flames was observed in autoignition of n -butane in the RCM used here, and it was realized that the final compression conditions in the RCM correspond to the upper end of the low-temperature range of the positive temperature dependence region of ignition delay. Then the combustion tests with PFJ were carried out and it was demonstrated that the onset of combustion can be controlled by PFJ, and it was revealed that PFJ has a potential for the ignition timing control of the homogeneous charge compression ignition engine.

Effects of Heat Release Rate on NOx Time History in Diesel Combustion.

For determining the optimum combination of combustion control techniques to reduce NOx emission from diesel engines, it is important to clarify the effects of each technique not only on the NOx emission but also on its time history during combustion. In this paper, NOx concentration in the combustion chamber of a rapid compression machine has been measured by using a total gas sampling method. In order to elucidate the relation between NOx history and heat release rate, air temperature, nozzle hole size and air motion are varied to control the heat release process. The results show that NOx emission is not solely dependent upon initial combustion. Air utilization in the main diffusive combustion phase has great influence on NOx formation and its decay. NOx formation is accelerated by activation of the initial stage of the main combustion when using a nozzle with small holes.

The influence of fuel properties on the heat release in DI-diesel engines

The description of the heat release of DI-diesel engines by means of the double-Vibe-model leads to a strong analogy with only six free parameters. Thus, a calculation method has been worked out according to Vibe's proposal of the ‘logarithmic anamorphosis’ for simple Vibe-functions. This method allows, contrary to conventional methods, the determination of all six parameters from experimental data independently of any assumptions made before. It also shows shorter calculation times. The reliability of the process has been verified by using the data of 54 test runs of a DI-diesel engine using gas oil and rape-oil as well as rape methyl ester. A dependency between fuel properties and Vibe-parameters has been proved. Boiling characteristic, fuel viscosity and also the cetane number control the premixed and the diffusion combustion phase. The premixed combustion phase is influenced by the ignition delay and the atomization quality, the diffusion combustion phase is primarily formed by the amount of converted fuel.

Features of vaporization and combustion of diesel fuels

This article examines certain features of combustion in automotive and tractor diesel engines for fuels of various compositions: commercial fuels, blends of commercial fuels with individual hydrocarbons, and blends of different individual hydrocarbons. Concludes that along with the influence of the cetane number (CN), the fuel volatility also has a substantial influence on the basic indexes of diesel operation. Points out that the indexes of the fast combustion phase and the content of nitrogen oxides in the exhaust gas will depend on the degree of fuel vaporization during the ignition delay period; the indexes of the diffusion combustion phase and the content of carbon in the exhaust gas will depend on the quantity of fuel injected after the start of combustion and on the rate of its vaporization.