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A production version of a V-8 engine was redesigned to run on partially premixed charge compression ignition (PCCI) combustion mode with conventional diesel fuel. The objective of the PCCI combustion experiments was to obtain low engine-out nitrogen oxide (NOx) and after-treatment tolerant soot emission level. Two fuel injection strategies were used during the PCCI combustion experiments: a) pilot-with-main injection strategy (Pil-M), b) pilot-with-main-and-post (PMP) injection strategy. In the Pil-M injection strategy, a significant fraction of the fuel was delivered early during the compression stroke. The early pilot helped to prepare a lean-mixture of enhanced homogeneity before the combustion was initiated. The combustion of this pilot injection followed by the main combustion helped to reduce soot for a constant NOx value. The pilot-injection timing and quantity had to be selected appropriately to retain the fuel-efficiency.

Dual-fuel combustion using liquid fuels with differing reactivity has been shown to achieve low-temperature combustion with moderate peak pressure rise rates, low soot and NOx emissions, and high indicated efficiency. Varying fractions of gasoline-type and diesel-type fuels enable operation across a range of low- and mid-load operating conditions. Expanding the operating range to cover the full operating range of a heavy-duty diesel engine, while maintaining the efficiency and emissions benefits, is a key objective. With dissimilar properties of the two utilized fuels lying at the heart of the dual-fuel concept, a tool for enabling this load range expansion is altering the properties of the two test fuels - this study focuses on altering the reactivity of the diesel fuel component. Tests were conducted on a 13L six-cylinder heavy-duty diesel engine modified to run dual-fuel combustion with port gasoline injection to supplement the direct diesel injection.

Low temperature combustion through in-cylinder blending of fuels with different reactivity offers the potential to improve engine efficiency while yielding low engine-out NOx and soot emissions. A Navistar MaxxForce 13 heavy-duty compression ignition engine was modified to run with two separate fuel systems, aiming to utilize fuel reactivity to demonstrate a technical path towards high engine efficiency. The dual-fuel engine has a geometric compression ratio of 14 and uses sequential, multi-port-injection of a low reactivity fuel in combination with in-cylinder direct injection of diesel. Through control of in-cylinder charge reactivity and reactivity stratification, the engine combustion process can be tailored towards high efficiency and low engine-out emissions. Engine testing was conducted at 1200 rpm over a load sweep.

Recognition of Dimethyl Ether (DME) as an alternative fuel has been growing recently due to its fast evaporation and ignition in application of compression-ignition engine. Most importantly, combustion of DME produces almost no particulate matter (PM). The current study provides a further understanding of the combustion process in DME reacting spray via experiment done in a constant volume combustion chamber. Formaldehyde (CH2O), an important intermediate species in hydrocarbon combustion, has received much attention in research due to its unique contribution in chemical pathway that leads to the combustion and emission of fuels. Studies in other literature considered CH2O as a marker for UHC species since it is formed prior to diffusion flame. In this study, the formation of CH2O was highlighted both temporally and spatially through planar laser induced fluorescence (PLIF) imaging at wavelength of 355-nm of an Nd:YAG laser at various time after start of injection (ASOI).

Extensive empirical work indicates that exhaust gas recirculation (EGR) is effective to lower the flame temperature and thus the oxides of nitrogen (NOx) production in-cylinder in diesel engines. Soot emissions are reduced in-cylinder by improved fuel/air mixing. As engine load increases, higher levels of intake boost and fuel injection pressure are required to suppress soot production. The high EGR and improved fuel/air mixing is then critical to enable low temperature combustion (LTC) processes. The paper explores the properties of the Fuels for Advanced Combustion Engines (FACE) Diesel, which are statistically designed to examine fuel effects, on a 0.75L single cylinder engine across the full range of load, spanning up to 15 bar IMEP. The lower cetane number (CN) of the diesel fuel improved the mixing process by prolonging the ignition delay and the mixing duration leading to substantial reduction of soot at low to medium loads, improving the trade-off between NOx and soot.

Diesel engine manufacturers have faced stringent emission regulations for oxides of nitrogen and particulate emissions for the last two decades. The emission challenges have been met with a host of technologies such as turbocharging, exhaust gas recirculation, high- pressure common rail fuel injection systems, diesel aftertreatment devices, and electronic engine controls. The next challenge for diesel engine manufacturers is fuel-economy regulations starting in 2014. As a prelude to this effort the department of energy (DOE) has funded the Supertruck project which intends to demonstrate 50% brake-thermal efficiency on the dynamometer while meeting US 2010 emission norms. In order to simultaneously meet the emission and engine efficiency goals in the cost effective manner engine manufacturer have adopted a systems approach, since individual fuel saving technologies can actually work against each other if fuel economy is not approached from a total vehicle perspective.

A 13 L HD diesel engine was converted to run as a flame propagation engine using the HEDGE™ Dual-Fuel concept. This concept consists of pre-mixed gasoline ignited by a small amount of diesel fuel - i.e., a diesel micropilot. Due to the large bore size and relatively high compression ratio for a pre-mixed combustion engine, high levels of cooled EGR were used to suppress knock and reduce the engine-out emissions of the oxides of nitrogen and particulates. Previous work had indicated that the boosting of high dilution engines challenges most modern turbocharging systems, so phase I of the project consisted of extensive simulation efforts to identify an EGR configuration that would allow for high levels of EGR flow along the lug curve while minimizing pumping losses and combustion instabilities from excessive backpressure. A potential solution that provided adequate BTE potential was consisted of dual loop EGR systems to simultaneously flow high pressure and low pressure loop EGR.

A production V-8 engine was redesigned to run on low temperature combustion (LTC) with conventional Diesel fuel. Two fuel injection strategies were used to attain reduction in soot and NOx; a) early premixed injection strategy: fuel injected early during the compression stroke and b) late premixed injection strategy: fuel injected close to TDC with heavy EGR. The early premixed injection strategy yielded low NOx and soot but struggled to vaporize the fuel as noted in unburned hydrocarbons readings. The late premixed injection strategy introduced the fuel at higher in-cylinder temperatures and densities, improving the fuel's vaporization and limited the unburned hydrocarbon and carbon monoxide. The use of high EGR and high injection pressure for late premixed injection strategy provided sufficiently long ignition delay that resulted in partially premixed cylinder charge before combustion, and thereby prevented high soot, even in presence of high EGR.

This paper investigates the effects of variable valve actuation on combustion in a Diesel engine. Early inlet valve closing (EIVC) lowered the pressure and temperature during the compression stroke, resulting in a longer ignition delay as the fuel mixed more homogenously with the charge air ahead of combustion. Combustion was characterized by prominent cool flame chemistry and a faster, more energetic, premixed combustion. Tests were performed on a 6.4L V8 engine at loads up to 5 bar BMEP. The use of EIVC showed significant reductions of soot (above 90%) and fuel efficiency improvements (of 5%) with NOx levels below the US 2010 standard of 0.2g/bhp-hr. The improvements in emissions and fuel economy came from controlling in-cylinder temperatures and optimizing combustion phasing. For a constant engine-out NOx emission, EIVC improved fuel economy as the amount of EGR and the engine back pressure requirement were reduced.

Natural gas quality, in terms of the volume fraction of higher hydrocarbons, strongly affects the auto-ignition characteristics of the air-fuel mixture, the engine performance and its controllability. The influence of natural gas composition on engine operation has been investigated both experimentally and through chemical kinetic based cycle simulation. A range of two component gas mixtures has been tested with methane as the base fuel. The equivalence ratio (0.3), the compression ratio (19.8), and the engine speed (1000 rpm) were held constant in order to isolate the impact of fuel autoignition chemistry. For each fuel mixture, the start of combustion was phased near top dead center (TDC) and then the inlet mixture temperature was reduced. These experimental results have been utilized as a source of data for the validation of a chemical kinetic based full-cycle simulation.

This paper discusses the compression ratio influence on maximum load of a Natural Gas HCCI engine. A modified Volvo TD100 truck engine is controlled in a closed-loop fashion by enriching the Natural Gas mixture with Hydrogen. The first section of the paper illustrates and discusses the potential of using hydrogen enrichment of natural gas to control combustion timing. Cylinder pressure is used as the feedback and the 50 percent burn angle is the controlled parameter. Full-cycle simulation is compared to some of the experimental data and then used to enhance some of the experimental observations dealing with ignition timing, thermal boundary conditions, emissions and how they affect engine stability and performance. High load issues common to HCCI are discussed in light of the inherent performance and emissions tradeoff and the disappearance of feasible operating space at high engine loads.

Homogeneous Charge Compression Ignition (HCCI) has been proposed for natural gas engines in heavy duty stationary power generation applications. A number of researchers have demonstrated, through simulation and experiment, the feasibility of obtaining high gross indicated thermal efficiencies and very low NOx emissions at reasonable load levels. With a goal of eventual commercialization of these engines, this paper sets forth some of the primary challenges in obtaining high brake thermal efficiency from production feasible engines. Experimental results, in conjunction with simulation and analysis, are used to compare HCCI operation with traditional lean burn spark ignition performance. Current HCCI technology is characterized by low power density, very dilute mixtures, and low combustion efficiency. The quantitative adverse effect of each of these traits is demonstrated with respect to the brake thermal efficiency that can be expected in real world applications.

Dimethyl Ether (DME) is considered a clean alternative fuel to diesel due to its soot-free combustion characteristics and its capability to be produced from renewable energy sources rather than fossil fuels such as coal or petroleum. To mitigate the effect of strong wave dynamics on fuel supply lines caused due to the high compressibility of DME and to overcome its low lubricity, a hydraulically actuated electronic unit injector (HEUI) with pressure intensification was used. The study focuses on high pressure operation, up to 2000 bar, significantly higher than pressure ranges reported previously with DME. A one-dimensional HEUI injector model is built in MATLAB/SIMULINK graphical software environment, to predict the rate of injection (ROI) profile critical to spray and combustion characterization.

In this work, an innovative piston bowl design that physically divides the combustion chamber into a central zone and a peripheral zone is employed to assist the control of the ethanol-diesel combustion process via heat release shaping. The spatial combustion zone partition divides the premixed ethanol-air mixture into two portions, and the combustion event (timing and extent) of each portion can be controlled by the temporal diesel injection scheduling. As a result, the heat release profile of ethanol-diesel dual-fuel combustion is properly shaped to avoid excessive pressure rise rates and thus to improve the engine performance. The investigation is carried out through theoretical simulation study and empirical engine tests. Parametric simulation is first performed to evaluate the effects of heat release shaping on combustion noise and engine efficiency and to provide boundary conditions for subsequent engine tests.

Diesel aided by gasoline low temperature combustion offers low NOx and low soot emissions, and further provides the potential to expand engine load range and improve engine efficiency. The diesel-gasoline operation however yields high unburned hydrocarbons (UHC) and carbon monoxide (CO) emissions. This study aims to correlate the chemical origins of the key hydrocarbon species detected in the engine exhaust under diesel-gasoline operation. It further aims to help develop strategies to lower the hydrocarbon emissions while retaining the low NOx, low soot, and efficiency benefits. A single-cylinder research engine was used to conduct the engine experiments at a constant engine load of 10 bar nIMEP with a fixed engine speed of 1600 rpm. Engine exhaust was sampled with a FTIR analyzer for speciation investigation.

This study investigates the impact of transient engine operation on the emissions formed during a tip-in procedure. A medium-duty production V-8 diesel engine is used to conduct experiments in which the rate of pedal position change is varied. Highly-dynamic emissions instrumentation is implemented to provide real-time measurement of NOx and particulate. Engine subsystems are analyzed to understand their role in emissions formation. As the rate of pedal position change increases, the emissions of NOx and particulates are affected dramatically. An instantaneous load increase was found to produce peak NOx values 1.8 times higher and peak particulate concentrations an order of magnitude above levels corresponding to a five-second ramp-up. The results provide insight into relationship between driver aggressiveness and diesel emissions applicable to development of drive-by-wire systems. In addition, they provide direct guidance for devising low-emission strategies for hybrid vehicles.

Low temperature combustion through in-cylinder blending of gasoline and diesel offers the potential to improve engine efficiency while yielding low engine-out soot and NOx emissions. This investigation utilized 3-D KIVA combustion simulation to guide the development of viable dual-fuel low temperature combustion strategies for heavy-duty applications. Model-based combustion optimization was performed at 1531rpm and 11 bar BMEP for a 12.4 L heavy-duty truck engine. Various engine operating parameters were explored through design of experiments (DoE). The parameters involved in the optimization process included compression ratio, air-fuel ratio, EGR rate, gasoline-to-diesel ratio, and diesel injection strategy (i.e., single-diesel injection vs. two-diesel injections, diesel injection timings, and the split ratio between two-diesel injections). Optimal cases showed near zero soot emissions and very low NOx emissions.

The use of gasoline fuels in compression ignition engines, with or without diesel pilots, has shown encouraging progress in engine efficiency and emissions. The dual fuel combustion of gasoline-diesel offers the flexibility of modulating the cylinder charge reactivity, but an accurate and reliable control over the ignition in the dual fuel applications is more challenging than in classical engines. In this work, the gasoline-diesel dual fuel operation is investigated on a single cylinder research engine. The effects of the intake boost, exhaust gas recirculation (EGR) rates, diesel/gasoline ratio, and diesel injection timing are studied in regard to the ignition control. The results indicate that at low load, a diesel pilot can improve the cylinder charge reactivity and reduce emissions of incomplete combustion products.

Modern diesel engines manufactured for commercial vehicles are calibrated to meet EPA emissions regulations. Many of the technologies and strategies typically incorporated to meet emissions targets compromise engine performance and efficiency. When used in military applications, however, engine performance and efficiency are of utmost importance in combat conditions or in remote locations where fuel supplies are scarce. This motivates the study of the potential to utilize the flexibility of emissions-reduction technologies toward optimizing engine performance while still keeping the emissions within tolerable limits. The study was conducted on a modern medium-duty International V-8 diesel engine with variable geometry turbocharger (VGT) and exhaust gas recirculation (EGR). The performance-emissions tradeoffs were explored using design of experiments and response surface methodology.

Paper details the design approach and performance of a high-pressure common rail fuel injection system used with Propane-DME mixtures targeting high injection pressures on a light duty 2.2L inline-4 compression ignition engine. The study estimates the bulk modulus of elasticity based on the hardware geometry and operating pressures to assess the compressibility of Propane and DME across a range of pressures typical of the LD engine application. The compressibility factor ranges from 500 to 3000 bar, significantly lower than the theoretical values for the conditions tested. The high-pressure pump performance is optimized via the implementation of an inlet metering valve operated on a crank-angle open/close sequence to control pressure at the common rail.