Tailoring Charge Reactivity Using In-Cylinder Generated Reformate for Gasoline Compression Ignition Strategies

In-cylinder reforming of injected fuel during an auxiliary negative valve overlap (NVO) period can be used to optimize main-cycle combustion phasing for low-load Low-Temperature Gasoline Combustion, where highly dilute mixtures can lead to poor combustion stability. The objective of this work is to examine the effects of reformate composition on main-cycle engine performance for a research gasoline. A custom alternate-fire sequence with nine pre-conditioning cycles was used to generate a common exhaust temperature and composition boundary condition for a cycle-of-interest. Performance metrics such as main-period combustion stability and total cycle efficiency were collected for these custom cycles. The NVO-produced reformate stream was also separately collected using a dump valve apparatus and characterized in detail using both gas chromatography and photoionization mass spectroscopy. To facilitate gas sample analysis, sampling experiments were conducted using a five-component gasoline surrogate (iso-octane, n-heptane, ethanol, 1-hexene, and toluene) that matched the molecular composition, 50% boiling point, and ignition characteristics of the research gasoline. For the gasoline, it was found that the most advanced NVO start-of-injection (SOI) led to the most advanced main-cycle 10% burn angle. The effect was more pronounced as the fraction of total fuel injected in the NVO period increased. With the most retarded NVO SOI, shorter residence times and piston spray impingement limited the opportunity for injected fuel decomposition. For the gasoline surrogate, the most advanced NVO SOI had reduced reactivity relative to more intermediate NVO SOI, which was attributed to rapid in-cylinder mixing that led to a large amount of fuel quench in the piston crevice. For all NVO periods, combustion phasing advanced as the main-period fueling decreased. Slower kinetics for leaner mixtures were offset by a combination of increased bulk-gas temperature from higher charge specific heat ratios and increased fuel reactivity due to higher charge reformate fractions.

Electric Turbo Compounding Applied to a CI Engine: A Numerical Evaluation of Different Layouts

At present, the application of turbocharging in compression ignition (CI) engines represents almost all of the applications, especially for transportation where fuel efficiency and low emissions are the main targets. Following this approach, the possibility to couple an electric drive to the turbocharger (electric turbo compound, ETC) to recover the residual energy of the exhaust gases is becoming more and more attractive, as demonstrated by several studies around the world. The present paper shows the first numerical results of a research program under way which is focused on the comparison of the benefits resulting from the application of two ETC configurations to a four cylinders CI engine (1561 cm3). In the first configuration, called single-ETC, a variable geometry turbocharger (VGT) is coupled to an electric generator (mechanic connection); in the second, called dual ETC, the two turbomachines (the variable nozzle turbine and the compressor) are separated and each one is coupled to its own electric machine. Starting from the experimental maps of the turbine and compressor, the complete engine model was created using the AVL BOOST one-dimension code. Compared with the no-ETC engine, the adoption of the single-ETC shows interesting benefits in term of energy recovery at the highest engine speeds and loads, with consequent decrease of fuel consumption. Dual ETC allows the operation of turbine and compressor at different speeds with further reduction of the total brake specific fuel consumption.

Effects of Fuel Quantity on Soot Formation Process for Biomass-Based Renewable Diesel Fuel Combustion

Soot formation process was investigated for biomass-based renewable diesel fuel, such as biomass to liquid (BTL), and conventional diesel combustion under varied fuel quantities injected into a constant volume combustion chamber. Soot measurement was implemented by two-color pyrometry under quiescent type diesel engine conditions (1000 K and 21% O2 concentration). Different fuel quantities, which correspond to different injection widths from 0.5 ms to 2 ms under constant injection pressure (1000 bar), were used to simulate different loads in engines. For a given fuel, soot temperature and KL factor show a different trend at initial stage for different fuel quantities, where a higher soot temperature can be found in a small fuel quantity case but a higher KL factor is observed in a large fuel quantity case generally. Another difference occurs at the end of combustion due to the termination of fuel injection. Additionally, BTL flame has a lower soot temperature, especially under a larger fuel quantity (2 ms injection width). Meanwhile, average soot level is lower for BTL flame, especially under a lower fuel quantity (0.5 ms injection width). BTL shows an overall low sooting behavior with low soot temperature compared to diesel, however, trade-off between soot level and soot temperature needs to be carefully selected when different loads are used.

Rapidly Pulsed Reductants for Diesel NOx Reduction With Lean NOx Traps: Comparison of Alkanes and Alkenes as the Reducing Agent

Lean NOx Traps (LNTs) are often used to reduce NOx on smaller diesel passenger cars where urea-based Selective Catalytic Reduction (SCR) systems may be difficult to package. However, the performance of LNTs at temperatures above 400°C needs to be improved. The use of Rapidly Pulsed Reductants (RPR) is a process in which hydrocarbons are injected in rapid pulses ahead of the LNT in order to improve its performance at higher temperatures and space velocities. This approach was developed by Toyota and was originally called Di-Air (Diesel NOx aftertreatment by Adsorbed Intermediate Reductants) [1]. There is a vast parameter space that needs to be explored in order to maximize the NOx conversion at high temperatures and flow rates while minimizing the fuel penalty associated with the hydrocarbon injections. Four parameters were identified as important for RPR operation: (1) the flow field and reductant mixing uniformity; (2) the pulsing parameters including the pulse frequency, duty cycle, and rich magnitude; (3) the reductant type; and (4) the catalyst composition, including the type and loading of precious metal, the type and loading of NOx storage material, and the amount of oxygen storage capacity (OSC). In this study, RPR performance was assessed between 150°C and 650°C with several reductants including dodecane, propane, ethylene, propylene, H2, and CO. A novel injection and mixer system was designed that allowed for the investigation of previously unexplored areas of high frequency injections up to f = 100Hz. Under RPR conditions, H2, CO, dodecane, and C2H4 provided approximately 80% NOx conversion at 500°C, but at 600°C the conversions were significantly lower, ranging from 40 to 55%. The NOx conversion with C3H8 was low across the entire temperature range, with a maximum conversion of 25% near 300°C and essentially no conversion at 600°C. In contrast, C3H6 provided greater than 90% NOx conversion over a broad range of temperature between 280°C and 630°C. Among the hydrocarbons, this suggested that the high temperature NOx conversion with RPR improves as the reactivity of the hydrocarbon increases.

Scavenged Pre-Chamber on a Gas Engine for Light Duty Truck

This work presents an experimental investigation of advanced combustion of extremely lean natural gas / air mixture in a gas fueled automotive engine with a scavenged pre-chamber. The pre-chamber, which was designed and manufactured in-house, is scavenged with natural gas and is installed into a modified cylinder head of a gas fueled engine for a light duty truck. For initial pre-chamber ignition tests and optimizations, the engine is modified into a single cylinder one. The pre-chamber is equipped with a spark plug, fuel supply and a miniature pressure transducer. This arrangement allows a simultaneous crank angle resolved pressure measurement in the pre-chamber and in the main combustion chamber and provides important validation data for computational fluid dynamics (CFD) simulations. The results of the tests and initial optimizations show that the pre-chamber engine is able to operate within a significantly wider range of mixture composition than the conventional spark ignition engine. Full load operation of the pre-chamber engine is feasible with stoichiometric mixture (compatible with a three-way catalyst), without excessive thermal loading of components. At low load operation, the results show low NOx emissions with a high potential to fulfil current and future NOx limits without lean NOx exhaust gas after-treatment. The scavenged pre-chamber helps to increase the combustion rate mainly in the initial phase of combustion. However, significant unburned hydrocarbons emissions due to incomplete combustion need further optimizations. Thermal efficiency of lean operation of the engine with the pre-chamber compared to the conventional spark ignition system operated in stoichiometric conditions shows approximately 13% improvement.

Lubricant Flow Optimization of Large Two Stroke Marine Diesel Engine Piston Ring Packs

Approaching a characterization of different contributors to the lube oil balance of an engine becomes important when aiming at enhancing lubrication performance and reducing its contribution to exhaust gas emissions. It is essential to quantify relevant data helping to determine lubrication losses related to particular tribosystem components. Recent activities focused on rating distinct tribosystem component effects on their contribution to total lube oil consumption and the possibility to most effectively modify those. This paper thus describes the most effective tribosystem component modifications, consisting of the application of a substantially modified piston ring pack and the introduction of lube oil accumulating grooves in order to considerably enhance lubrication performance. A proper prediction of piston ring pack dynamics and tribodynamic effects on the lube oil film is essential to design a superior piston ring pack in terms of an optimized piston running behaviour and lube oil transportation. One major step designing such a ring pack is based on the consequent application of a novel 3D piston ring pack simulation tool to enhance lube oil transportation characteristics and distribution. Lube oil accumulating grooves are introduced to reduce lubrication losses due to so called ring pack spray. The ring pack spray is a result of accumulated lubricant in the pressurized piston ring pack expanding into the scavenge air receiver during the scavenging phase. Mentioned effect was analysed in detail in order to determine the amount of related lubricant losses. Investigations in this context lead to the application of lube oil accumulating grooves and hence can be considered an important design aspect to reduce total lube oil consumption. Tribosystem performance validation was performed on the basis of the application of an SO2 tracing technology on a full scale engine test in order to determine relevant tribosystem component modifications in real time. The sulphur content of fuel and lube oil considerably influences the formation of particulate matter in the exhaust gas, following chemical reactions of sulphur oxidation. Hence detecting SO2 in the exhaust gas is a direct measure to determine the amount of lubricant in the exhaust gas composition. Finally this report demonstrates measurement results describing the superior performance of the modified tribosystem.

Evaluation of Spark Plug and Timing Configurations on the Fuel Consumption, Combustion Stability, and Emissions of a Large-Bore, Two-Stroke, Natural Gas Engine

Emissions compliance is a driving factor for internal combustion engine research pertaining to both new and old technologies. New standards and compliance requirements for off-road spark ignited engines are currently under review and include greenhouse gases. To continue operation of legacy natural gas engines, research is required to increase or maintain engine efficiency, while reducing emissions of carbon monoxide, oxides of nitrogen, and volatile organic compounds such as formaldehyde. A variety of technologies can be found on legacy, large-bore natural gas engines that allow them to meet current emissions standards — these include exhaust after-treatment, advanced ignition technologies, and fuel delivery methods. The natural gas industry uses a variety of spark plugs and tuning methods to improve engine performance or decrease emissions of existing engines. The focus of this study was to examine the effects of various spark plug configurations along with spark timing to examine any potential benefits. Spark plugs with varied electrode diameter, number of ground electrodes, and heat ranges were evaluated against efficiency and exhaust emissions. Combustion analyses were also conducted to examine peak firing pressure, location of peak firing pressure, and indicated mean effective pressure. The test platform was an AJAX-E42 engine. The engine has a bore and stroke of 0.216 × 0.254 meters (m), respectively. The engine displacement was 9.29 liters (L) with a compression ratio of 6:1. The engine was modified to include electronic spark plug timing capabilities along with a mass flow controller to ensure accurate fuel delivery. Each spark plug configuration was examined at ignition timings of 17, 14, 11, 8, and 5 crank angle degrees before top dead center. The various configurations were examined to identify optimal conditions for each plug comparing trade-offs among brake specific fuel consumption, oxides of nitrogen, methane, formaldehyde, and combustion stability.

TWC-SCR Aftertreatment System Evaluation for a Lean Burn Gasoline Engine Operating in HCCI, SACI, and SI Combustion Modes

Low temperature and dilute Homogenous Charge Compression Ignition (HCCI) and Spark Assisted Compression Ignition (SACI) can improve fuel economy and reduce engine-out NOx emissions to very low values, often less than 30 ppm. However, these combustion modes are unable to achieve stringent future regulations such as SULEV 30 without the use of lean aftertreatment. Though active selective catalytic reduction (SCR) with urea injection and lean NOx traps (LNT) have been investigated as options for lean gasoline engines, a passive TWC-SCR system is investigated in this work because it avoids the urea storage and dosing hardware of a urea SCR system, and the high precious metal cost of an LNT. The TWC-SCR concept uses periodic rich operation to produce NH3 over a TWC to be stored on an SCR catalyst for subsequent NOx conversion during lean operation. In this work a laboratory study was performed with a modified 2.0 L gasoline engine that was cycled between lean HCCI and rich SACI operation, or between lean and rich SI (spark ignited) combustion, to evaluate NOx conversion and reduced fuel consumption. Different lambda values during rich operation and different times held in rich operation were investigated. Results are compared to a baseline case in which the engine is always operated at stoichiometric conditions. SCR system simulations are also presented that compare system performance for different levels of stored NH3. With the configuration used in this study, lean/rich HCCI/SACI operation showed a maximum NOx conversion efficiency of 10%, while lean/rich SI operation showed a maximum NOx conversion efficiency of 60%. However, if the low conversion efficiency of lean/rich HCCI/SACI operation could be improved through higher brick temperatures or additional SCR bricks, simulation results indicate TWC-SCR aftertreatment has the potential to provide near-zero SCR-out NOx concentration and increased system fuel efficiency. In these simulations, fuel efficiency improvement relative to stoichiometric SI were 7 to15% for lean/rich HCCI/SACI with zero tailpipe NOx and −1 to 5% for lean/rich SI with zero tailpipe NOx emissions. Although previous work indicated increased time for NH3 to start forming over the TWC during rich operation, less NH3 production over the TWC per fuel amount, and increased NH3 slip over the SCR catalyst for advanced combustion systems, if NOx conversion efficiency could be enhanced, improvements in fuel economy and low engine-out NOx from advanced combustion modes would more than make up for these disadvantages.

Effects of Ammonia Gas Mixed Into Intake Air on Combustion and Emissions Characteristics in Diesel Engine

This paper reports on the experimental results of the combustion and emission characteristics of a conventional diesel engine mixed ammonia (NH3) gas into the intake air, and discusses its usability. In the experiments, NH3 gas was injected into the intake pipe of the diesel engine by a gas injector. The diesel engine has a natural aspiration single cylinder with 7.7 kW rated power at 1500 rpm and a diesel injection system to inject diesel fuel into the cylinder. As experimental results on the combustion characteristics, it was confirmed that the compression and maximum pressures in the cylinder decreased and the ignition timing delayed with increasing the NH3 gas injection quantity. On the emission characteristics in the exhaust gas, NH3, water (H2O) and nitrous oxide (N2O) increased and carbon dioxide (CO2) decreased proportionally to the NH3 gas injection quantity. In contract, the nitrogen oxide (NO) was nearly the same. Moreover, it was confirmed that NH3 can be reduced by reacting with NO in a selective catalytic reduction (SCR) system.

Effects of Gas Composition on Combustion, Emission and Knocking Characteristics of Marine Lean Burn Gas Engine

The present study has experimentally investigated the effect of fuel gas composition on the combustion, emission and knocking characteristics of a marine lean burn gas engine. The experiments was carried out using the lean burn gas engine, which has the rated power output of 400 kW with spark ignition pre-chamber system. The various compositions of the base fuel gas (Japanese city gas) changed by supplying propane-based LPG (liquefied petroleum gas), butane-based LPG and hydrogen. This paper reports in detail the experimental results on the combustion and emission characteristics of the lean burn gas engine affected by the fuel gas composition. The experimental results showed that the composition of fuel gas mixed with P-LPG and B-LPG has a small effect on the combustion characteristics, and the operation of the engine is hardly affected. However, the addition of hydrogen causes the rise of the maximum combustion pressure and the attention should be paid on the ratio of hydrogen in the fuel gas. With regard to the emission characteristics, the NOx emission increased with increasing the ratio of P-LPG, B-LPG and hydrogen in the base fuel gas. The CO emission increased with increasing the ratio of P-LPG and B-LPG and decreased with increasing the ratio of hydrogen in the base fuel gas. It is expected that such the tendencies depended on the carbon quantity in the fuel gas. In addition, it was found that the knocking characteristics are associated with the methane number of fuel gas.