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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.

Synthetic fuels (e-fuels) synthesized from H2 and CO by renewable electricity are expected as the next- generation diesel fuels and two types of e-fuels have received extensive attention: Fischer-Tropsch (FT) fuel and Oxymethylene dimethyl ether (OME). In this study the effects of OME blending ratios with 0 to 50 vol.% in FT fuels on combustion, emissions and spray characteristics in diesel engines are investigated. The results suggest that the OME blends to FT fuels suppressed the deterioration in combustion efficiency under low intake oxygen concentration conditions. The smoke emissions of FT fuels and OME blended fuels were both lower than those of diesel fuel and decreased with the increase in the OME blend ratio, and the soot-NOx trade-off relation in diesel engines can be improved.

This study applies high-speed particle image velocimetry (HS-PIV) and flame image velocimetry (HS-FIV) to show flow fields under the effect of varied swirl ratios in a small-bore optical compression-ignition engine. The base swirl ratio and maximum swirl ratio conditions were applied to investigate structures, magnitude and turbulence distribution of the in-cylinder flow as well as the flow within the flame. For each swirl ratio, 100 individual cycles were measured for PIV analysis at motoring conditions and then another 100 cycles for FIV analysis at firing conditions. The derived flow fields were ensemble averaged to show flow structure evolution while the spatial filtering method was applied to extract high-frequency flow component for the analysis of turbulence distributions. The results showed that the intake air flow generates undefined, chaotic flow fields, which are followed by a gradual production of an asymmetric swirl flow.

The authors have reported significant smoke reduction in twin shaped semi-premixed diesel combustion with a newly designed combustion chamber to distribute the first and the second sprays into upper and lower layers. However, the first stage premixed combustion tends to advance far from the TDC, resulting in lowering of thermal efficiencies. In this report, improvement of thermal efficiency by optimizing the combustion phase with lower ignitability fuels was identified with the divided combustion chamber. The experiment was conducted with four fuels with different cetane numbers. The first stage premixed combustion can be retarded to the optimum phase with the fuel with cetane number 38, establishing high efficiencies.

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.

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.

Spark knock suppression with hydrogen addition was investigated at two engine speeds (2000 rpm and 4800 rpm). The experimental results showed that the spark knock is strongly suppressed with increasing hydrogen fraction at 2000 rpm while the effect is much smaller at 4800 rpm. To explain these results, chemical kinetic analyses with a two-zone combustion model were performed. The calculated results showed that the heat release in the end gas zone rises in two stages with a remarkable appearance of low temperature oxidation (LTO) at 2000 rpm, while a single stage heat release without apparent LTO process is presented at 4800 rpm due to the shorter residence time in the low temperature region.

This paper presents a study on the effects of the engine size and rotation speed on diesel combustion characteristics and engine performance of two differently sized diesel engines (85 mm and 135 mm bores). For simplification of the evaluation, the experimental conditions were set based on the similarity rules proposed by Chikahisa. The combustion characteristics and the indicated thermal efficiencies were compared for the small and the large engines at the same engine speed. To examine the effects of the velocities of the in-cylinder gas and the fuel spray on the combustion and the thermal efficiency, the engine speed was changed in the small engine, while maintaining a non-dimensional engine speed.

To improve the combustion characteristics in semi-premixed diesel combustion, consisting in the first-stage premixed combustion of the primary fuel injection and the second-stage spray combustion of the secondary injection, the effect of splitting the primary injection was investigated in a diesel engine and analyzed with a CFD. The indicated thermal efficiency improves due to reductions in heat transfer losses to the in-cylinder wall and the combustion noise is suppressed with the split primary injections. The CFD analysis showed that the reduction in heat transfer loss with the split primary injections is due to a decrease in the combustion quantity near the combustion chamber wall.

The Dual-Fuel (DF) combustion is a promising technology for efficient, low NOx and low exhaust particulate matter (PM) engine operation. To achieve equivalent performance to a DF engine with only the use of conventional liquid fuel, this study proposes the implementation of an on-board fuel reformation process by piston compression. For concept verification, DF combustion tests with representative reformed gas components were conducted. Based on the results, the controllability of the reformed gas composition by variations in the operating conditions of the reformer cylinder were discussed.

Semi-premixed diesel combustion with a twin peak shaped heat release with the two-stage fuel injection (twin combustion) has the potential to establish efficient, low emission, and low noise operation. However, with twin combustion at low loads the indicated thermal efficiencies are poorer than at medium loads due to the lower combustion efficiencies. In this report, to increase the combustion efficiencies at low loads, the thermal efficiency related parameters were investigated in a 0.55 L single cylinder diesel engine. The results show that the indicated thermal efficiency improves with increases in the intake gas temperatures at low loads. However, at the higher loads where the combustion efficiencies are somewhat higher the indicated thermal efficiencies decrease with increases in the intake gas temperatures due to increases in the cooling losses.

To extend the operational range of premixed diesel combustion, fuel reformation by piston induced compression of rich homogeneous air-fuel mixtures was conducted in this study. Reformed gas compositions and chemical processes were first simulated with the chemistry dynamics simulation, CHEMKIN Pro, by changing the intake oxygen content, intake air temperature, and compression ratio. A single cylinder diesel engine was utilized to verify the simulation results. With the simulation and experiments, the characteristics of the reformed gas with respect to the reformer cylinder operating condition were obtained. Further, the thermal decomposition and partial oxidation reaction mechanisms of the fuel in extremely low oxygen concentrations were obtained with the characteristics of the gas production at the various reaction temperatures.

To monitor emission-related components/systems and to evaluate the presence of malfunctioning or failures that can affect emissions, current diesel engine regulations require the use of on-board diagnostics (OBD). For diesel particulate filters (DPF), the pressure drop across the DPF is monitored by the OBD as the pressure drop is approximately linear related to the soot mass deposited in a filter. However, sudden acceleration may cause a sudden decrease in DPF pressure drop under cold start conditions. This appears to be caused by water that has condensed in the exhaust pipe, but no detailed mechanism for this decrease has been established. The present study developed an experimental apparatus that reproduces rapid increases of the exhaust gas flow under cold start conditions and enables independent control of the amount of water as well as the gas flow rate supplied to the DPF.

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.

Diesel particulate filters (DPF) are widely used in diesel engines, and forced regeneration is necessary to remove particulate matter (PM) accumulating on the DPF. This may be achieved with fuel injected after the main combustion is complete, the socalled “post fuel injection”, and supplied to the diesel oxidation catalyst (DOC) upstream of the DPF. This increases the exhaust gas temperature in the DOC and the DPF is regenerated with the high temperature gas flow. In most cases, the post fuel injection takes place at 30-90CA ATDC, and fuel may impinge on and adhere to the cylinder liner wall in some cases. Buddie and Pischinger [1] have reported a lubricant oil dilution with the post fuel injection by engine tests and simulations, and adhering fuel is a cause of worsening fuel consumption. In this paper, the impingement and adhesion of post diesel fuel injections on the cylinder liner was investigated by an optical method with a high pressure constant volume chamber (ϕ110mm, 883cm3).

The engine performance and the exhaust gas emissions in a dual fuel compression ignition engine with natural gas as the main fuel and a small quantity of pilot injection of diesel fuel with the ultra-high injection pressure of 250 MPa as an ignition source were investigated at 0.3 MPa and 0.8 MPa IMEP. With increasing injection pressure the unburned loss decreases and the thermal efficiency improves at both IMEP conditions. At the 0.3 MPa IMEP the THC and CO emissions are significantly reduced when maintaining the equivalence ratio of natural gas with decreasing the volumetric efficiency by intake gas throttling, but the NOx emissions increase and excessive intake gas throttling results in a decrease in the indicated thermal efficiency. Under the 250 MPa pilot injection condition simultaneous reductions in the NOx, THC, and CO emissions can be established with maintaining the equivalence ratio of natural gas by intake gas throttling.

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.