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Turbocharged gasoline direct injection (GDI) engines are quickly becoming more prominent in light-duty automotive applications because of their potential improvements in efficiency and fuel economy. While EGR dilute and lean operation serve as potential pathways to further improve efficiencies and emissions in GDI engines, they also pose challenges for stable engine operation. Tests were performed on a single-cylinder research engine that is representative of current automotive-style GDI engines. Baseline cases were performed under steady-state operating conditions where combustion phasing and dilution were varied to determine the effects on indicated efficiency and combustion stability. Sensitivity studies were then carried out by introducing binary low-high perturbation of spark timing and injection duration on a cycle-by-cycle basis under EGR dilute and lean operation to determine dominant feedback mechanisms.

Large cyclic variability along with increased combustion noise present in low temperature combustion (LTC) modes of internal combustion engines has driven the need for fast response, robust sensors for diagnostics and feedback control. Accelerometers have been shown as a possible technology for diagnostics and feedback control of advanced LTC operation in internal combustion engines. To make better use of this technology, an improved understanding is necessary of the effect of energy release from the combustion process on engine surface vibrations. This study explores the surface acceleration response for a single-cylinder engine operating with homogeneous charge compression ignition (HCCI) combustion. Preliminary investigation of the engine surface accelerations is conducted using a finite element analysis of the engine cylinder jacket along with consideration of cylindrical modes of the engine cylinder.

This study investigated the effects of soybean- and coconut-derived biodiesel fuels on combustion characteristics in a 1.7-liter direct injection, common rail diesel engine. Five sets of fuels were studied: 2007 ultra low sulfur diesel (ULSD), 5% and 20% volumetric blends of soybean biodiesel with ULSD (soybean B5 and B20), and 5% and 20% volumetric blends of coconut biodiesel with ULSD (coconut B5 and B20). In conventional diesel combustion mode, particulate matter (PM) and nitrogen oxides (NOx) emissions were similar for all fuels studied except soybean B20. Soybean B20 produced the lowest PM but the highest NOx emissions. Compared with conventional diesel combustion mode, high efficiency clean combustion (HECC) mode, achieved by increased EGR and combustion phasing, significantly reduced both PM and NOx emissions for all fuels studied at the expense of higher hydrocarbon (HC) and carbon monoxide (CO) emissions and an increase in fuel consumption (less than 4%).

Current political and environmental concerns are driving renewed efforts to develop techniques for improving the efficiency of internal combustion engines. A detailed thermodynamic analysis of an engine and its components from a 1st and 2nd Law perspective is necessary to characterize system losses and to identify efficiency opportunities. We have developed a method for performing this analysis using simulation results from commercially available engine-modeling software packages such as WAVE® from Ricardo, Inc., and GT-Power™ from Gamma Technologies, Inc. Results from the simulation are post-processed to compute thermodynamic properties such as internal energy, enthalpy, entropy, and availability (or exergy) which are required to perform energy and availability balances for the system. This analysis is performed for all major engine components (turbocharger, intercooler, EGR cooler, etc.) and for the engine as a whole as a function of crank angle over an entire engine cycle.

High-efficiency clean combustion (HECC) modes provide simultaneous reductions in diesel particulate matter and nitrogen-oxides emissions while retaining efficiencies characteristic of normal diesel engines. Fuel parameters may have significant impacts on the ability to operate in HECC modes and on the emissions produced in HECC modes. In this study, 3 diesel-range fuels and 2 oxygenated blends are burned in both normal and HECC modes at 3 different engine conditions. The results show that fuel effects play an important role in the emissions of hydrocarbons, particulate matter, and carbon monoxide but do not significantly impact NOx emissions in HECC modes. HECC modes are achievable with 5% biodiesel blends in addition to petroleum-based and oil-sands derived fuels. Soot precursor and oxygenated compound concentrations in the exhaust were observed to generally increase with the sooting tendency of the fuel in HECC modes.

We report experimental observations of cyclic combustion variability during the transition between propagating flame combustion and homogeneous charge compression ignition (HCCI) in a single-cylinder, stoichiometrically fueled, spark-assisted gasoline engine. The level of internal EGR was controlled with variable valve actuation (VVA), and HCCI combustion was achieved at high levels of internal EGR using the VVA system. Spark-ignition was used for conventional combustion and was optionally available during HCCI. The transition region between purely propagating combustion and HCCI was mapped at multiple engine speeds and loads by incrementally adjusting the internal EGR level and capturing data for 2800 sequential cycles. These measurements revealed a complex sequence of high COV, cyclic combustion variations when operating between the propagating flame and HCCI limits.

Internal combustion engines are operated under conditions of high exhaust gas recirculation (EGR) to reduce NOx emissions and promote enhanced combustion modes such as HCCI. However, high EGR under certain conditions also promotes nonlinear feedback between cycles, leading to the development of combustion instabilities and cyclic variability. We employ a two-zone phenomenological combustion model to simulate the onset of combustion instabilities under highly dilute conditions and to illustrate the impact of these instabilities on emissions and fuel efficiency. The two-zone in-cylinder combustion model is coupled to a WAVE engine-simulation code through a Simulink interface, allowing rapid simulation of several hundred successive engine cycles with many external engine parametric effects included.

Thermal conductivity detection has long been used in gas chromatography to detect hydrogen and other diatomic gases in a gas sample. Thermal conductivity instruments that are not coupled to gas chromatographs are useful for detecting hydrogen in binary gas mixtures, but suffer from significant cross-interference from other gas species that are separated when the detector is used with a gas chromatograph. This study reports a method for using a commercially-available thermal conductivity instrument to detect and quantify hydrogen in a diesel exhaust stream. The instrument time response of approximately 40 seconds is sufficient for steady-state applications. Cross-interference from relevant gas species are quantified and discussed. Measurement uncertainty associated with the corrections for the various species is estimated and practical implications for use of the instrument and method are discussed.

We investigate lean-fueling cyclic dispersion in spark ignition engines in terms of experimental nonlinear mapping functions representing the connection between past and future combustion events. Nonlinear mapping functions provide a relatively easy method for identifying the deterministic dynamics associated with lean combustion instability, even in the presence of very high levels of noise. Observed experimental maps appear to have strong similarities to those predicted by an existing nonlinear spark ignition engine model. Differences between the observed map and model predictions become more pronounced at very lean fueling and high residual fraction. Map function details are shown to be useful in model validation, identifying model deficiencies, and comparing the characteristics of different engines. We expect that such maps will also be useful for developing real-time control strategies.