Modeling NO and Soot Emissions With Gas Compressibility

A multidimensional engine combustion code was used to model NO and soot emissions from a heavy duty Cummins Diesel engine with a compression ratio of 16. The code solves the gas calculation in a moving curvilinear coordinate system. The code includes a 13 species chemistry model that calculates the rate of formation of each species from the fuel conversion time and the species equilibrium concentration. The code also models fuel injection, spray impingement and secondary spray breakup. The engine was tested with 10% EGR in the intake by mass, a swirl ratio of 2.1 and an engine speed of 1500 rpm. The engine was tested at 3 different injection timings. The consequence of including compressibility effects is also studied. The Redlich-Kwong model was used to calculate the deviation of the gases within the combustion chamber from ideal gas behavior. The computational results were compared to the values of pressure, NO and soot emissions obtained from experiments. At the high compression ratio that the engine operates under, the ideal gas equation was found to under-predict the peak cylinder pressure by about 4%. The soot emissions were closely matched in both value and trend. Due to the inaccuracy of the equilibrium-based chemical model, the calculated NO emissions were higher than the experimental values. The evolution of the NO and soot emissions during the cycle was studied. The processes that form these emissions were identified.

Reducing Grid Dependency in Droplet Collision Modeling

A faster, more accurate replacement for existing collision algorithms has been developed. The method, called the NTC algorithm, is not grid dependent, and is much faster than older algorithms. Calculations with sixty thousand parcels required only a few CPU minutes. However, there is a significant need to develop mesh-independent momentum coupling between the gas and spray, so that the collision algorithm’s full accuracy can be fully realized.

A Study of the Effects of Radiation on Pollutant Emissions in Direct Injection Engines

The laminar flamelet combustion model was used to study the effects of radiation on chemistry in a direct injection engine. A two dimensional axisymmetric engine code with a simple mixing length turbulence model was used. Four state relationships for different conditions were obtained from laminar opposed flow diffusion flame calculations by considering gas and soot radiation heat loss using detailed gas and global soot kinetics. The effects of radiation on pollutant emissions were studied by using the four state relationships in the engine calculations.

Quantitative X-Ray Measurements of Diesel Spray Cores

A detailed knowledge of the fuel injection process is recognized as a key to the design of clean-burning and efficient combustion engines. As standards for pollutant emissions are tightened worldwide, such knowledge becomes more critical. Computer modeling of the combustion process relies on accurate measurements of the spray throughout its lifetime, and in particular knowledge of the near-nozzle region of the spray is of great importance. A number of techniques have been developed to study the properties of fuel sprays. However, all of these techniques are significantly limited in the region near the nozzle of high-pressure sprays. No mechanical or visible light probe is able to make non-intrusive and quantitative measurements of the spray in this region. We have been developing techniques to study sprays using synchrotron x-rays from the Advanced Photon Source at Argonne National Laboratory. We are using an intense, monochromatic x-ray beam as a probe to make time-resolved, quantitative measurements, of intermittent fuel sprays. These experiments have demonstrated that x-rays overcome many of the limitations of other techniques, allowing quantitative characterization of the spray with high time and position resolution. The x-ray technique enables us to make a time-resolved mapping of the mass distribution near the spray nozzle, even immediately adjacent to the orifice. With such a mapping of the mass a number of spray characteristics can be determined, such as the fuel volume fraction, the injection rate and total mass, the speed of the leading and trailing edges of the spray, etc. These quantitative measurements should allow more realistic computational modeling of sprays with better predictive power.

Response Surface Method Optimization of a HSDI Diesel Engine Equipped With a Common Rail Injection System

To overcome the trade-off between NOx and particulate emissions for future diesel vehicles and engines it is necessary to seek methods to lower pollutant emissions. The desired simultaneous improvement in fuel efficiency for future DI diesels is also a difficult challenge due to the combustion modifications that will be required to meet the exhaust emission mandates. This study demonstrates the emission reduction capability of EGR and other parameters on a High Speed Direct Injection (HSDI) diesel engine equipped with a common rail injection system using an RSM optimization method. Engine testing was done at 1757 rev/min, 45% load. The variables used in the optimization process included injection pressure, boost pressure, injection timing, and EGR rate. RSM optimization led engine operating parameters to reach a low-temperature and premixed combustion regime called the MK combustion region, and resulted in simultaneous reductions in NOx and particulate emissions without sacrificing fuel efficiency. It was shown that RSM optimization is an effective and powerful tool for realizing the full advantages of the combined effects of combustion control techniques by optimizing their parameters. It was also shown that through a close observation of optimization processes, a more thorough understanding of HSDI diesel combustion can be provided.

How Chemistry Controls Engine Design

A review of empirical engine data that exhibit the limits of the chemistry of fuel oxidation in engines is presented. These data have been compared to analyses using up to date fuel oxidation chemical analyses programs and shown to be in close agreement. The constraints caused by the fuel oxidation chemistry limitations are key determinants of the engine’s overall design, determining allowed intake conditions, fuel-air ratios, compression ratio requirements, and the need for such ancillary devices as those for exhaust emissions aftertreatment.

Effect of Injection Rate on the Performance and Emissions of a Direct-Injection Gasoline Engine in Comparison With the Port-Injection Operation

This paper presents a study on the effect of injection rate on the performance and emissions of a direct-injection gasoline engine operated with seven kinds of DI injection and a port-injection. The injection pressures were set at 0.3 and 7 MPa for port injection and DI operation modes respectively. The spray characteristics of DI injectors were obtained by measuring the SMD, droplet concentration and spray angle. The engine was run at a constant speed and load of 1000 rpm and 0.22 MPa of BMEP. The BSFC reduction of DI from port injection was 13% at most in which 4% was derived from the decrease in pumping loss and the remaining 9% was due to the improvement of the cycle efficiency. As for the injection rate effect in DI operation, the BSFC takes the minimum at a value of the injection rate where the maximum difference reached to 7%. It was revealed that this is due to the variation of the combustion efficiency and then corresponds to the behavior of droplet concentration. Soot emission correlated well with the SMD. Thus the performance and emissions were mostly explained by the spray characteristics.

Synchrotron X-Ray Measurement of Direct Injection Gasoline Fuel Sprays

A quantitative and time-resolved radiographic has been used to characterize direct-injection (Dl) gasoline sprays in near-nozzle region. The highly penetrative nature of x-rays promises the direct measurements of dense sprays that are difficult to study by visible-light optical techniques. Appropriate models were developed to determine the fuel volume fraction as a function of time and positions. The results also show quantitatively the strong asymmetry of the hollow-cone sprays studied here.

Orifice Diameter Effects on Diesel Fuel Jet Flame Structure

The effects of orifice diameter on several aspects of diesel fuel jet flame structure were investigated in a constant-volume combustion vessel under heavy-duty, direct-injection (DI) diesel engine conditions using Phillips research grade #2 diesel fuel and orifice diameters ranging from 45 μm to 180 μm. The overall flame structure was visualized with time-averaged OH chemiluminescence and soot luminosity images acquired during the quasi-steady portion of the diesel combustion event that occurs after the transient premixed burn is completed and the flame length is established. The lift-off length, defined as the farthest upstream location of high-temperature combustion, and the flame length were determined from the OH chemiluminescence images. In addition, relative changes in the amount of soot formed for various conditions were determined from the soot incandescence images. Combined with previous investigations of liquid-phase fuel penetration and spray development, the results show that air entrainment upstream of the lift-off length (relative to the amount of fuel injected) is very sensitive to orifice diameter. As orifice diameter decreases, the relative air entrainment upstream of the lift-off length increases significantly. The increased relative air entrainment results in a reduced overall average equivalence ratio in the fuel jet at the lift-off length and reduced soot luminosity downstream of the lift-off length. The reduced soot luminosity indicates that the amount of soot formed relative to the amount of fuel injected decreases with orifice diameter. The flame lengths determined from the images agree well with gas jet theory for momentum-driven, non-premixed turbulent flames.

Simulation of Multiphase Flow With Vaporization in DGI Engine Injector

The purpose of the paper is to present a simulation concept, which is able to take into account the most important phenomena that occur in the high-pressure swirl injector fuel flows, typical for the direct gasoline injection (DGI) engines. Used are two- (air, gasoline liquid) and three-phase (air, gasoline liquid and vapor) flow models. The most important characteristics of the flow were predicted. Both two- and three-phase flow simulation results show the formation of a thin conical sheet with an air core. Vaporization in the air core due to pressure drop below the saturation conditions was predicted in the three-phase flow simulation.