R. Vallinayagam

Combustion Stratification for Naphtha from CI Combustion to PPC

This study demonstrated the change in combustion homogeneity from conventional diesel combustion via partially premixed combustion towards HCCI. Experiments are performed in an optical diesel engine at a speed of 1200 rpm with diesel fuel. Single injection strategy is employed and the fuel is injected at a pressure of 800 bar. The cylinder pressure at TDC is maintained at 35 bar and a high-speed video of the combustion process is captured through optical piston. The high speed video is processed to study the combustion homogeneity based on an algorithm reported in previous studies. Starting from late fuel injection timings, the combustion homogeneity is investigated by advancing to early fuel injection timings. For late fuel injection timings, a direct link between fuel injection timing and combustion phasing is noticed. At advanced fuel injection timings, the start of combustion is independent of fuel injection timing. The combustion homogeneity for the transition from CI via PPC towards HCCI is also investigated for various levels of dilution by displacing oxygen with nitrogen in the inlet. The start of combustion was retarded with the increase in dilution, while the mixture homogeneity is enhanced due to longer ignition delay. To compensate for the retarded combustion phasing with dilution, the inlet air temperature is increased. The experimental results show that the high speed image is initially blue and then turned yellow, indicating soot oxidation. The images are processed to generate the level of stratification based on the image intensity. This study shows better combustion homogeneity for early fuel injection timing and higher level of dilution and temperature in the inlet.

Effect of Timing and Location of Hotspot on Super Knock during Pre-ignition

This work was sponsored by the Saudi Aramco under the FUELCOM II program and by King Abdullah University of Science and Technology. The computational simulations utilized the clusters at KAUST Supercomputing Laboratory and IT Research Computing.

Computational Study of Stratified Combustion in an Optical Diesel Engine

This work was funded by competitive research funding from King Abdullah University of Science and Technology (KAUST) under the Clean Combustion Research Centers research program. We also acknowledge funding from Saudi Aramco under the FUELCOM program. Finally, we would like to express our gratitude to our research Technician, Adrian I. Ichim for his support in carrying out the experiments at KAUST engine lab.

Effect of aromatics on combustion stratification and particulate emissions from low octane gasoline fuels in PPC and HCCI mode

The objective of this study was to investigate the effect of aromatic on combustion stratification and particulate emissions for PRF60. Experiments were performed in an optical CI engine at a speed of 1200 rpm for TPRF0 (100% v/v PRF60), TPRF20 (20% v/v toluene + 80% PRF60) and TPRF40 (40% v/v toluene + 60% PRF60). TPRF mixtures were prepared in such a way that the RON of all test blends was same (RON = 60). Single injection strategy with a fuel injection pressure of 800 bar was adopted for all test fuels. Start of injection (SOI) was changed from early to late fuel injection timings, representing various modes of combustion viz HCCI, PPC and CDC. High-speed video of the in-cylinder combustion process was captured and one-dimensional stratification analysis was performed from the intensity of images. Particle size, distribution and concentration were measured and linked with the in-cylinder combustion images. Results showed that combustion advanced from CDC to PPC and then attained a constant value in HCCI mode. In PPC and HCCI region, the soot mass concentration was significantly reduced as premixing was improved due to longer ignition delay. The particle number was lower for the late injection and becomes higher as the injection timing advanced to PPC and HCCI mode. While the soot particles were almost nuclear model with the size range of 5nm~17nm and as combustion transited from CDC via PPC to HCCI, the particle size became larger. For TPRF blends, the increased intake air temperature was required to maintain same combustion phasing as that of PRF60. With the addition of toluene to PRF60, the soot concentration increased, which was in-line with the increased intensity (yellow) of combustion images. The degree of stratification was higher for TPRF20 and TPRF40 when compared to PRF60.

Fuel effect on combustion stratification in partially premixed combustion

The literature study on PPC in optical engine reveals investigations on OH chemiluminescence and combustion stratification. So far, mostly PRF fuel is studied and it is worthwhile to examine the effect of fuel properties on PPC. Therefore, in this work, fuel having different octane rating and physical properties are selected and PPC is studied in an optical engine. The fuels considered in this study are diesel, heavy naphtha, light naphtha and their corresponding surrogates such as heptane, PRF50 and PRF65 respectively. Without EGR (Intake O2 = 21%), these fuels are tested at an engine speed of 1200 rpm, fuel injection pressure of 800 bar and pressure at TDC = 35 bar. SOI is changed from late to early fuel injection timings to study PPC and the shift in combustion regime from CI to PPC is explored for all fuels. An increased understanding on the effect of fuel octane number, physical properties and chemical composition on combustion and emission formation is obtained. High-speed images of the combustion process are analyzed for each and every fuel and in-cylinder phenomenon is associated with rate of heat release and in-cylinder pressure. Based on the intensity of the images, stratification analysis is performed.The results of the analysis show that CA50 decreases for all fuels from late to early SOI wherein PPC is realized. According to the reactivity of fuels, intake air temperature is increased to comply with the combustion phasing of baseline diesel. When studying the effect of physical properties of fuels, premixed effect and lean combustion are observed for PRF0 compared to diesel. The engine emissions of THC and CO are higher for PRF0 than diesel, while soot concentration is reduced. Diesel showed more stratified combustion than PRF0 despite having same RON due to the effect of physical properties. The effect of fuel octane number on PPC is suppressed due to temperature effect; intake air temperature is increased to 140°C and 90°C for PRF65 and PRF50. PRF0 lacked LTR phase and combustion was noted to be more premixed than PRF50 and PRF65 at SOI = -10 CAD (aTDC). The intensity of the combustion images is brighter for high RON fuels than PRF0 due to physical effects, while octane number effect is not realized due to higher intake air temperature. While THC and CO emissions decreased with the increase in RON, NOX emission increased due to increased intake air temperature. When comparing real fuels, soot concentration is lower for light naphtha when compared to diesel and heavy naphtha.

Combustion homogeneity and emission analysis during the transition from CI to HCCI for FACE I gasoline

Low temperature combustion concepts are studied recently to simultaneously reduce NOX and soot emissions. Optical studies are performed to study gasoline PPC in CI engines to investigate in-cylinder combustion and stratification. It is imperative to perform emission measurements and interpret the results with combustion images. In this work, we attempt to investigate this during the transition from CI to HCCI mode for FACE I gasoline (RON = 70) and its surrogate, PRF70. The experiments are performed in a single cylinder optical engine that runs at a speed of 1200 rpm. Considering the safety of engine, testing was done at lower IMEP (3 bar) and combustion is visualized using a high-speed camera through a window in the bottom of the bowl.From the engine experiments, it is clear that intake air temperature requirement is different at various combustion modes to maintain the same combustion phasing. While a fixed intake air temperature is required at HCCI condition, it varies at PPC and CI conditions between FACE I gasoline and PRF70. Three zones are identified 1) SOI = -180 to -80 CAD (aTDC) is HCCI zone 2) SOI = -40 to -20 CAD (aTDC) is PPC zone 3) After SOI = -15 CAD (aTDC) is CI zone. Combustion duration, ignition delay, start of combustion and CA90 (crank angle at which 90% of fuel burnt) are comparable between FACE I gasoline and PRF70. The combustion images show a prominent soot flame at CI condition, while only blue coloured premixed flames are visible at PPC condition for both the fuels. PRF70 seems to have a pronounced premixed effect when compared to FACE I gasoline at early injections, showing a decreased level of stratification. NOX emission and soot concentration decreases from CI condition and attains a constant zero value at HCCI condition for both FACE I gasoline and PRF70. CO and CO2 emissions matches between FACE I gasoline and PRF70 at PPC and CI condition, while CO emission is lower for PRF70 at HCCI condition.

Analysis of transition from HCCI to CI via PPC with low octane gasoline fuels using optical diagnostics and soot particle analysis

In-cylinder visualization, combustion stratification, and engine-out particulate matter (PM) emissions were investigated in an optical engine fueled with Haltermann straight-run naphtha fuel and corresponding surrogate fuel. The combustion mode was transited from homogeneous charge compression ignition (HCCI) to conventional compression ignition (CI) via partially premixed combustion (PPC). Single injection strategy with the change of start of injection (SOI) from early to late injections was employed. The high-speed color camera was used to capture the in-cylinder combustion images. The combustion stratification was analyzed based on the natural luminosity of the combustion images. The regulated emission of unburned hydrocarbon (UHC), carbon monoxide (CO) and nitrogen oxides (NOX) were measured to evaluate the combustion efficiency together with the in-cylinder rate of heat release. Soot mass concentration was measured and linked with the combustion stratification and the integrated red channel intensity of the high-speed images for the soot emissions. The nucleation nanoscale particle number and the particle size distribution were sampled to understand the effect of combustion mode switch.

Diethyl Ether as an Ignition Enhancer for Naphtha Creating a Drop in Fuel for Diesel

The research reported in this publication was supported by Saudi Aramco under the FUELCOM program and by the King Abdullah University of Science and Technology (KAUST) with competitive research funding given to the Clean Combustion Research Center (CCRC). Finally, we would like to express our gratitude to our Research Technician, Adrian. I. Ichim for his support in carrying out the engine experiments at KAUST engine lab.

Improving Vegetable Oil Fueled CI Engine Characteristics Through Diethyl Ether Blending

The research reported in this publication was supported by Saudi Aramco under the FUELCOM program and by the King Abdullah University of Science and Technology (KAUST) with competitive research funding given to the Clean Combustion Research Center (CCRC). Finally, we would like to express our gratitude to our Research Technician, Adrian. I. Ichim for his support in carrying out the engine experiments at KAUST engine lab.