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The effect of direct-injected fuel on particle size distributions (PSDs) of particulate matter emitted from dual-fuel combustion strategies was investigated. The PSD data were acquired from a light-duty single-cylinder diesel engine operated using conventional diesel combustion (CDC) and two diesel/natural gas dual-fuel combustion strategies. Three different direct-injection (DI) fuels (diesel, 2,6,10-trimethyldodecane, and a primary reference fuel blend) and two different injector nozzles were studied. The DI fuels were chosen to have similar energy and ignition characteristics (heat of combustion and cetane number) but different physical and chemical properties (volatility, aromatics %, viscosity, density). The two nozzles (with different orifice diameter and spray angle) allowed a wide range in DI fuel quantity for the dual-fuel combustion strategies.

The effect of fuel physical properties on the ignition and combustion characteristics of diesel fuels was investigated in a heavy-duty 2.52 L single-cylinder engine. Two binary component fuels, one comprised of farnesane (FAR) and 2,2,4,4,6,8,8-heptamethylnonane (HMN), and another comprised of primary reference fuels (PRF) for the octane rating scale (i.e. n-heptane and 2,2,4-trimethylpentane), were blended to match the cetane number (CN) of a 45 CN diesel fuel. The binary mixtures were used neat, and blended at 25, 50, and 75% by volume with the baseline diesel. Ignition delay (ID) for each blend was measured under identical operating conditions. A single injection was used, with injection timing varied from −12.5 to 2.5 CAD. Injection pressures of 50, 100, and 150 MPa were tested. Observed IDs were consistent with previous work done under similar conditions with diesel fuels. The shortest IDs were seen at injection timings of −7.5 CAD.

The effects of jet fuel properties on compression ignition engine operation were investigated under high-load conditions for jet fuels with varying cetane number. A single-cylinder oil-test engine (SCOTE) with 2.44 L displacement was used to test a baseline #2 diesel fuel with a cetane number of 43, a Jet-A fuel with a cetane number of 47, and two mixtures of Jet-A and a Fishcer-Tropsch JP-8 with cetane numbers of 36 and 42, respectively. The engine was operated under high-load conditions corresponding to traditional diesel combustion, using a single injection of fuel near TDC. The fuels were tested using two different intake camshafts with closing times of -143 and -85 CAD BTDC. Injection timing sweeps were performed over a range of injection timings near TDC for each camshaft. The apparent net heat release rate (AHRR) data showed an increase in the premixed burn magnitude as cetane number decreased in agreement with previous work.

Detailed properties of particulate matter (PM) emissions from a gasoline direct injection (GDI) engine were analyzed in terms of size, morphology, and nanostructures, as gasoline and its ethanol blend E20 were used as a fuel. PM emissions were sampled from a 0.55L single-cylinder GDI engine by means of a scanning mobility particle sizer (SMPS) for size measurements and a self-designed thermophoretic sampling device for the subsequent analyses of size, morphology and nanostructures using a transmission electron microscope (TEM). The particle sizes were evaluated with variations of air-fuel equivalence ratio and fuel injection timing. The most important result from the SMPS measurements was that the number of nucleation-mode nanoparticles (particularly those smaller than 10 - 15 nm) increased significantly as the fuel injection timing was advanced to the end-of-injection angle of 310° bTDC.

The effect of equivalence ratio on the particulate size distribution (PSD) in a spark-ignited, direct-injected (SIDI) engine was investigated. A single-cylinder, four-stroke, spark-ignited direct-injection engine fueled with certification gasoline was used for the measurements. The engine was operated with early injection during the intake stroke. Equivalence ratio was swept over the range where stable combustion was achieved. Throughout this range combustion phasing was held constant. Particle size distributions were measured as a function of equivalence ratio. The data show the sensitivity of both engine-out particle number and particle size to global equivalence ratio. As equivalence ratio was increased a larger fraction of particles were due to agglomerates with diameters ≻ 100 nm. For decreasing equivalence ratio smaller particles dominate the distribution. The total particle number and mass increased non-linearly with increasing equivalence ratio.

This work experimentally investigates the impact of premixed fuel composition (methane/ethane, methane/propane, and methane/hydrogen mixtures having equivalent chemical energy) and pilot reactivity (cetane number) on diesel-pilot injection (DPI) combustion performance and emissions, with an emphasis on the pilot ignition delay (ID). To support the experimental pilot ignition delay trends, an analysis technique known as Mixing Line Concept (MLC) was adopted, where the cold diesel surrogate and hot premixed charge are envisioned to mix in a 0-D constant volume reactor to account for DPI mixture stratification. The results show that the dominant effect on pilot ignition is the pilot fuel cetane number, and that the premixed fuel composition plays a minor role. There is some indication of a physical effect on ignition for cases containing premixed hydrogen.

Local deposition of thermal energy can be used to assist the combustion process of low cetane number (CN) fuels in compression-ignition engines, here termed energy-assisted compression ignition (EACI). In the current work, a commercial ceramic glow plug, operated beyond its conventional operation range, was used as the ignition assistant (IA) and sensitivity of fuel jet ignition to operation parameters was studied for two fuels using EACI in an optical engine. A design-of-experiments (DoE) study was devised to determine which engine parameters influenced the energy-assisted pilot injection ignition process the most. The DoE was constructed with four parameters: injection pressure, injected mass, injection timing, and ignition assistant temperature. The fuels used were F24 (Jet-A with military additives) with a cetane number of 48 and a cetane number 35 fuel mixture consisting of 60% F24 and 40% of an alcohol-to-jet fuel (ATJ), blended on a volumetric basis.

In this study, the impacts of fuel volatility and reactivity on combustion stability and emissions were studied in a light-duty single-cylinder research engine for a three-injection catalyst heating operation strategy with late post-injections. N-heptane and blends of farnesane/2,2,4,4,6,8,8-heptamethylnonane were used to study the impacts of volatility and reactivity. The effect of increased chemical reactivity was also analysed by comparing the baseline #2 diesel operation with a pure blend of mono-ether components (CN > 100) representative of potential high cetane oxygenated bioblendstocks and a 25 vol.% blend of the mono-ether blend and #2 diesel with a cetane number (CN) of 55. At constant reactivity, little to no variation in combustion performance was observed due to differences in volatility, whereas increased reactivity improved combustion stability and efficiency at late injection timings.

The combined impacts of engine speed and fuel reactivity on energy-assisted compression-ignition (EACI) combustion using a commercial off-the-shelf (COTS) ceramic glow plug for low-load operation werexxz investigated. The COTS glow plug, used as the ignition assistant (IA), was overdriven beyond its conventional operation range. Engine speed was varied from 1200 RPM to 2100 RPM. Three fuel blends consisting of a jet-A fuel with military additives (F24) and a low cetane number alcohol-to-jet (ATJ) sustainable aviation fuel (SAF) were tested with cetane numbers (CN) of 25.9, 35.5, and 48.5. The ranges of engine speed and fuel cetane numbers studied are significantly larger than those in previous studies of EACI or glow-plug assisted combustion, and the simultaneous variation of engine speed and fuel reactivity are unique to this work. For each speed and fuel, a single-injection of fixed mass was used and the start of injection (SOI) was swept for each IA power.

Experiments were performed on a small-bore optically accessible engine to investigate diesel pilot ignition (DPI) and reactivity controlled compression ignition (RCCI) dual-fuel combustion strategies with direct injection of natural gas and diesel. Parametric variations of pilot ratio were performed. Natural luminosity and OH chemiluminescence movies of the combustion processes were captured at 28.8 and 14.4 kHz, respectively. These data were used to create ignition maps, which aided in comparing the propagation modes of the two combustion strategies. Lower pilot ratios resulted in lower initial heat release rates, and the initial ignition sites were generally smaller and less luminous; for increased pilot ratios the initial portion of the heat release was larger, and the ignition sites were large and bright. Comparisons between diesel pilot ignition and reactivity controlled compression ignition showed differences in combustion propagation mechanisms.

The influence of a split-injection strategy on energy-assisted compression-ignition (EACI) combustion of low-cetane number sustainable aviation fuels was investigated in a single-cylinder direct-injection compression-ignition engine using a ceramic ignition assistant (IA). Two low-cetane number fuels were studied: a low-cetane number alcohol-to-jet (ATJ) sustainable aviation fuel (SAF) with a derived cetane number (DCN) of 17.4 and a binary blend of ATJ with F24 (Jet-A fuel with military additives, DCN 45.8) with a blend DCN of 25.9 (25 vol.% F24, 75 vol.% ATJ). A pilot injection mass sweep (3.5-7.0 mg) with constant total injection mass and an injection dwell sweep (1.5-3.0 ms) with fixed main injection timing was performed. Increasing pilot injection mass was found to reduce cycle-to-cycle combustion phasing variability by promoting a shorter and more repeatable combustion event for the main injection with a shorter ignition delay.