Raul Lima Ochoterena

Effects of Multiple Injections on Engine-Out Emission Levels Including Particulate Mass from an HSDI Diesel Engine

The effects of multiple injections on engine-out emissions from a high-speed direct injection (HSDI) diesel engine were investigated in a series of experiments using a single cylinder research engine. Injection sequences in which the main injection was split into two, three and four pulses were tested and the resulting emissions (NOx, CO HC and particulate matter), torque and cylinder pressures were compared to those obtained with single injections. Together with the number of injections, the effects of varying the dwell time were also investigated. It was found that dividing the main injection into two parts lowered the engine-out particulate and CO emissions and increased fuel efficiency. However, it also resulted in increased NOx emissions. Further, using double injections reduced the peak rate of heat release (RoHR) and increased RoHR in the later stages of the combustion without changing the combustion duration, resulting in a more even distribution of RoHR during the combustion, which is believed to be the main reason for the changes in fuel consumption and engine-out emission levels. When the number of injections was increased to three or four and the dwell time was prolonged the RoHR decreased, the combustion duration increased and the CA50 was retarded. Consequently, NOx emissions were reduced but the fuel efficiency also declined, and emissions of particulate mater, CO and HC rose.

In-cylinder soot imaging and emissions of stratified combustion in a spark-ignited spray-guided direct-injection gasoline engine

The combustion in a spark-ignited spray-guided gasoline direct-injection engine operating in a stratified mode has been studied by in-cylinder imaging of the fuel, OH*, and soot distributions. Information on the fuel distribution was obtained by laser-induced fluorescence imaging of the aromatic molecules in the gasoline. The OH* and soot distributions were simultaneously visualized by detection of the natural emissions at 306 nm (OH*) and around 530 nm (soot) using two intensified charge-coupled device cameras. In addition to the in-cylinder observations, engine-out soot emissions, NOx, and HC were measured. The engine was operated at a speed of 2000 r/min and an indicated mean effective pressure of 2.5 bar, with a fully open throttle, resulting in a globally lean combustion with a fuel–air equivalence ratio of about 0.25. The gasoline was injected in single or double injections by an outward-opening piezo-actuated injector. The combustion was ignited efficiently at locally fuel-rich conditions. The soot formation and oxidation were investigated for the two injection strategies, each with three injection timings and two fixed ignition timings. The results showed that soot was efficiently formed and oxidized. From the in-cylinder measurements, it could be seen that the soot luminescence intensity quickly rose and then declined, while the combustion temperature was still increasing. Furthermore, the OH* intensity was still increasing as the soot luminescence was declining. The soot incandescence peak intensity occurred at a crank angle degree close to 50 per cent mass burned, and the OH* intensity peak arose later, shortly before the maximum soot temperature around top dead centre (TDC). When the injection timing was retarded, with constant ignition timing with respect to injection, it was found that the total soot luminosity increased. In addition, less OH* chemiluminescence was observed during the decrease of the soot incandescence, implying conditions less favourable for efficient soot oxidation in the later part of the combustion for retarded injections. This was confirmed by the engine-out soot emission measurements, which showed increased soot levels as the injection was retarded. It was also found that fuel impinged on the spark plug during the injections, resulting in a persistent jet flame close to the spark plug in the centre of the cylinder, which is believed to contribute to engine-out soot emissions.

Optical studies of spray development and combustion characterization of oxygenated and Fischer-Tropsch fuels

Optical studies of combusting diesel sprays were done on three different alternative liquid fuels and compared to Swedish environmental class 1 diesel fuel (MK1). The alternative fuels were Rapeseed Oil Methyl Ester (RME), Palm Oil Methyl Ester (PME) and Fischer-Tropsch (FT) fuel. The studies were carried out in the Chalmers High Pressure High Temperature spray rig under conditions similar to those prevailing in a direct-injected diesel engine prior to injection. High speed shadowgraphs were acquired to measure the penetration of the continuous liquid phase, droplets and ligaments, and vapor penetration. Flame temperatures and relative soot concentrations were measured by emission based, lineof- sight, optical methods. A comparison between previous engine tests and spray rig experiments was conducted in order to provide a deeper explanation of the combustion phenomena in the engine tests. Results pertaining to spray behavior show that high viscosity fuels have wider spray cone angles, smaller discharge coefficients (Cd) and shorter vapor penetration than low viscosity fuels. Continuous liquid phase penetration is related to differences in surface tension, viscosity and density; while the penetration of droplets and ligaments is related to volatility, their penetration is short for highly volatile fuels and long for low-volatility fuels. Engine tests show that particle matter (PM) emissions are generally lower when these alternative fuels are used, but the use of RME leads to increased NOx emissions correlating with elevated flame temperatures.

Soot Evolution in Multiple Injection Diesel Flames

In order to meet future emission regulations, various new combustion concepts are being developed, several of which incorporate advanced diesel injection strategies, e.g. multiple injections, offering attractive potential benefits. In this study the effects of split injections on soot evolution in diesel flames were investigated in a series of flame experiments performed using a high pressure, high temperature (HP/HT) spray chamber and laser-induced incandescence apparatus to measure soot volume fractions. The focus was on split injections with varied dwell times preceded by a short pilot. The results, which were analyzed and compared to results from engine tests, show that net soot production can be decreased by applying an appropriate split injection strategy.

Time and spatially resolved temperature measurements of a combusting diesel spray impinging on a wall

The interaction between a combusting diesel spray and a wall was studied by measuring the spray flame temperature time and spatially resolved. The influence of injection sequences, injection pressure and gas conditions on the heat transfer between the combusting spray and the wall was investigated by measuring the flame temperature during the complete injection event. The flame temperature was measured by an emission based optical method and determined by comparing the relative emission intensities from the soot in the flame at two wavelength intervals. The measurements were done by employing a monochromatic and non intensified high speed camera, an array of mirrors, interference filters and a beam splitter. The studies were carried out in the Chalmers High Pressure High Temperature (HP/HT) spray rig at conditions similar to those prevailing in a direct injected diesel engine prior to the injection of fuel. Fuel was injected into the combustion chamber by a common rail system using an injector with a single hole nozzle. The combusting spray impinged on a wall whose temperature was similar to the combustion chamber gas temperature. Results of these experiments show variations in the flame temperature as a consequence of the interaction between the combusting spray and the wall. There is a reduction in the flame temperature after impingement followed by a temperature rise as the wall is heated up by the flame. The effects caused by injection pressure, injection sequences and gas temperature lead to differences

High Speed Shadowgraph and Diffraction Based Imaging for Spray Characterisation and Combustion Studies

An abridged method for high speed shadowgraph and diffraction based imaging of combusting sprays, capable to discern among spray and flame regions is presented and discussed. The measurements were done in a pressure and temperature controlled combustion chamber under conditions similar to those prevailing in a direct injected diesel engine. A set of examples are shown where the visualisation and localisation of the liquid and gas phases of reacting sprays are possible regardless of the injection sequence which is implemented. Further, the penetration of the liquid and gas phases can be measured along a single injection with the possibility of doing spray characterisation and combusting studies of a single spray spatially resolved and as function of time.

Performance of a Heavy Duty DME Engine - the Influence of Nozzle Parameters on Combustion and Spray Development

DME was tested in a heavy duty diesel engine and in an optically accessible high-temperature and pressure spray chamber in order to investigate and understand the effect of nozzle parameters on emissions, combustion and fuel spray concentration. The engine study clearly showed that smaller nozzle orifices were advantageous from combustion, efficiency and emissions considerations. Heat release analysis and fuel concentration images indicate that smaller orifices result in higher mixing rate between fuel and air due to reductions in the turbulence length scale, which reduce both the magnitude of fuel-rich regions and the steepness of fuel gradients in the spray, which enable more fuel to burn and thereby shorten the combustion duration.