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Smoke emission from compression ignition (CI) engines is directly tied to fuel atomization, vaporization, mixing and combustion processes. Engine boundary conditions such as ambient pressures and temperatures, particularly at higher altitudes, have significant impacts on both available ignition energy and on the mixing-controlled combustion process. However, the effects of boundary conditions are difficult to explore without thorough pressure and temperature control of the engine intake air and exhaust gas at higher altitude conditions. The objective of this research is to investigate the relationship between engine smoke emission and engine power in a CI engine fueled with jet fuel at various ambient conditions including higher altitudes. A multi-cylinder compression-ignition engine was operated on a jet fuel at various ambient pressure and temperature conditions, as low as 60 kPa and -12°C, respectively. Single and multi-injection strategies were applied depending on engine power.

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.

Airborne compression-ignition engine operations differ significantly from those in ground vehicles, both in mission requirements and in operating conditions. Unique challenges exist in the aviation space, and electrification technologies originally developed for ground applications may be leveraged to address these considerations. One such technology, electrically assisted turbochargers (EATs), have the potential to address the following: increase the maximum system power output, directly control intake manifold air pressure, and reignite the engine at altitude conditions in the event of an engine flame-out. Sea-level experiments were carried out on a two-liter, four-cylinder compression-ignition engine with a commercial-off-the-shelf EAT that replaced the original turbocharger. The objective of these experiments was to demonstrate the technology, assess the performance, and evaluate control methods at sea level prior to altitude experimentation.

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.

A non-intrusive sensing technique to determine start of combustion for mixing-controlled compression-ignition engines was developed based on an accelerometer mounted to the engine block of a 4-cylinder automotive turbo-diesel engine. The sensing approach is based on a physics-based conceptual model for the signal generation process that relates engine block acceleration to the time derivative of heat release rate. The frequency content of the acceleration and pressure signals was analyzed using the magnitude-squared coherence, and a suitable filtering technique for the acceleration signal was selected based on the result. A method to determine start of combustion (SOC) from the acceleration measurements is presented and validated.

The applications of unmanned aerial vehicles (UAV) are growing exponentially with advances in hybrid powertrain architecture design tools. The thermal management system (TMS) as an integral part of the powertrain architecture greatly affects the system performance of aerial vehicles. In this study, a comparative analysis of two types of thermal management technologies for a UAV with a series-hybrid powertrain architecture was performed. Conventional TMS based on single-phase (no phase change) cooling technologies using air and liquid (e.g., antifreeze water mixture and oil) as heat transfer fluid has been commonly used because of simple design and operation, although it is considered to be inefficient and bulky. As advanced designs, phase change-based TMS is being slowly adopted although it promises superior cooling capabilities.

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.

An experimental investigation of non-intrusive combustion sensing was performed using a tri-axial accelerometer mounted to the engine block of a small-bore high-speed 4-cylinder compression-ignition direct-injection (CIDI) engine. This study investigates potential techniques to extract combustion features from accelerometer signals to be used for cycle-to-cycle engine control. Selection of accelerometer location and vibration axis were performed by analyzing vibration signals for three different locations along the block for all three of the accelerometer axes. A magnitude squared coherence (MSC) statistical analysis was used to select the best location and axis. Based on previous work from the literature, the vibration signal filtering was optimized, and the filtered vibration signals were analyzed. It was found that the vibration signals correlate well with the second derivative of pressure during the initial stages of combustion.

The objective of the study was to investigate the spray and combustion characteristics of Jet Propellant-8 (JP-8) using a high-pressure fuel injector which is capable of up to 250-MPa fuel injection pressure. Experiments were performed in a constant-pressure flow-through combustion chamber at the ambient conditions of 825 K and 6 MPa for the oxygen concentration of 0 and 21%. JP-8 was injected over a range of fuel injection pressures from 50 to 250 MPa for single injection events to establish a baseline operation. Pilot and post injections were used to study the effect of multiple injections on spray and combustion of the high-pressure fuel injector. Both pilot and post injection separation times and quantities were systematically varied. JP-8 spray and combustion events were imaged at 75 kHz using a combination of Mie scattering and OH* chemiluminescence imaging.

This research compares the spray development and combustion characteristics of jet propellant 8 (JP-8) and iso-paraffinic kerosene (IPK) through a range of diesel engine in-cylinder operating conditions. Non-reacting spray experiments were performed in a constant-pressure flow chamber with 99% nitrogen gas composition at constant temperature (900 K) and densities ranging from 11-56 kg/m3. Near-simultaneous, high-speed Mie and schlieren images of the spray were acquired to measure the liquid and vapor penetration lengths of the non-reacting jet. Reacting experiments, consisting of photodiode measurements and intensified high-speed movies of OH* chemiluminescence, were performed at the same thermodynamic conditions as the non-reacting experiments, except with a 21%/79% oxygen/nitrogen ambient gas composition. Measurements of the rate of injection, issued from a single-hole axial common-rail fuel injector, showed negligible differences between the fuels.

The objective of the study is to characterize combustion and performance of a multi-cylinder turbocharged direct-injection (DI) diesel engine at altitude conditions according to the International Standard Atmosphere (ISA). Experiments were performed on the 6.6-liter turbocharged DI diesel engine, a model similar to that of the Army’s Joint Light Tactical Vehicle. The engine was installed in the US Army Research Laboratory Small Engine Altitude Research Facility. Outside air temperature (OAT) and outside air pressure were independently controlled to match the ISA-OAT at selected altitude conditions: sea level, 1524, 3048, and 4572 m. The test engine is equipped with a single-stage variable nozzle turbocharger and Bosch CRIN 3 common-rail injection system. Three load conditions (i.e., low, mid, and high) were selected at 1400 rpm to investigate combustion and performance of the engine using Jet Propellant-8 (JP-8) fuel.

As published, Figures 4, 6, 22, and 26 contained errors and are corrected in the erratum.

The objective of this study is to optimize the injector power drive system for improved fuel injection quantity and timing control. The power drive system was optimized for improved injection repeatability under different operating conditions such as fuel supply pressures. A coupled simulation of injector electromagnetic, pintle (needle) rigid body motion and computational fluid dynamics (CFD) model was employed to generate the optimal values of the 1st stage current, the 1st stage on-time and the 2nd stage current. The simulation results were validated against the experimental data measured with a photo detector measurement system.

The objective of this study is to measure high-frequency, short-duration, actual liquid fuel spray events using a simple photo detector and validate the results with high-speed camera measurements. This paper presents an optical approach for detecting bulk fuel injection's temporal characteristics, i.e. opening delay and duration times. A key component in the measurement system is a commercially available low-cost photo detector which is shown to be highly effective for detecting high frequency, short duration spray events. The paper provides an in-depth discussion of a photo detector based measurement system, a test fixture, and its validation. Test results with a two-stage pulse-width-modulation (PWM) current controlled approach are provided for various operation parameter settings. Its effectiveness is validated by comparing with the results obtained with a high-speed camera.

Current regulations stipulate acceptable levels of particulate emissions based on the mass collected on filters obtained by sampling in diluted exhaust. Although precise, this gives us only aggregated information. If in addition to the mass based measurements, detailed chemical analysis of the particulate matter (PM) is performed, additional subtle information about the combustion process can be revealed. This paper reports the results of detailed chemical analysis of trace metal in the PM emitted from a single cylinder heavy-duty diesel engine. The trace metal concentrations are used as an indicator of oil consumption. Two techniques were used to make the trace metal concentration measurements. PM was captured on filters and trace metals were quantified with an Inductively Coupled Plasma Mass Spectrometer (ICPMS), and also an Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) was used to perform particle size and composition measurements in real time.

Significant amounts of particle-phase organic compounds are present in the exhaust of diesel vehicles. It is believed that some of these compounds have a greater impact on human health and the environment than other compounds. Therefore, it is of significant importance to speciate particle-phase organic compounds of diesel particulate matter (PM) to clarify the effects of PM on human health and the environment, and to understand the mechanisms of organic compounds formation in PM. A dilution source sampling system was incorporated into the exhaust measurement system of a single-cylinder heavy-duty direct-injection (D.I.) diesel engine. This system was designed specifically to collect fine organic aerosols from diesel exhaust. The detailed system is described in Kweon et al. [27].

A dilution source sampling system has been incorporated into the exhaust measurement system of a research single-cylinder diesel engine. To allow more detailed assessment of the individual chemical components of the diesel particulate matter (PM) the exhaust dilution system includes a residence time chamber (RTC) to allow for residence times of 30 to 60 seconds in the second stage of dilution before sampling. Samples are collected on a range of different filters where mass loading, elemental and organic carbon (ECOC), trace metals, sulfate ions (SO4), particle-phase organic compounds, and semi-volatile organic compounds are evaluated. In addition, particle size distributions have been determined using a scanning mobility particle sizer (SMPS). Results show that the chemical composition of the particulate matter is highly dependent on the engine operating conditions.

A study was performed in which the effects on the regulated emissions from a commercial small DI diesel engine were measured for different refinery-derived fuel blends. Seven different fuel blends were tested, of which two were deemed to merit more detailed evaluation. To investigate the effects of fuel properties on the combustion processes with these fuel blends, two-color pyrometry was used via optically accessible cylinderheads. Additional data were obtained with one of the fuel blends with a heavy-duty DI diesel engine. California diesel fuel was used as a baseline. The fuel blends were made by mixing the components typically found in gasoline, such as methyl tertiary-butyl ether (MTBE) and whole fluid catalytic cracking gasoline (WH-FCC). The mixing was performed on a volume basis. Cetane improver (CI) was added to maintain the same cetane number (CN) of the fuel blends as that of the baseline fuel.