Timothy J. Jacobs

Method and Detailed Analysis of Individual Hydrocarbon Species From Diesel Combustion Modes and Diesel Oxidation Catalyst

An undiluted exhaust hydrocarbon (HC) speciation method, using flame ionization detector (FID) gas chromatographs (GC), is developed to investigate HC species from conventional and low-temperature premixed charge compression ignition (PCI) combustion, from pre- and post-diesel oxidation catalyst (DOC) exhaust. This paper expands on previously reported work by describing in detail the method and effectiveness of undiluted diesel exhaust speciation and providing a more detailed analysis of individual HC species for conventional and PCI diesel combustion processes. The details provided regarding the effectiveness of the undiluted diesel exhaust speciation method include the use of a fuel response factor (RF) for HC species quantification and demonstration of its linearity, detection limit, accuracy and precision. The listing of individual HC species provides not only the information needed to design surrogate exhaust mixtures used in reactor tests and modeling studies, but also sheds light on PCI combustion and DOC characteristics. Significantly increased engine-out concentrations of acetylene, benzene and toluene support the theory that net soot reduction associated with PCI combustion occurs due to the reduction of soot formation from soot precursors. DOC oxidation behavior differs depending on the combustion characteristics, which change exhaust species and temperature.Copyright

Cylinder-to-cylinder variation sources in diesel low temperature combustion and the influence they have on emissions

Cylinder-to-cylinder variation in a multi-cylinder diesel engine was found to increase substantially when transitioning to a low-temperature combustion mode. This study was started to investigate the potential influence this effect could have on the emissions levels. Initial testing showed an imbalance in the fuel distribution that prompted this article to focus on data from before and after swapping two injectors under both conventional and low-temperature combustion modes. A significant improvement is observed in cylinder variation based both on visual heat release inspection and on mean effective pressure variation. This is likely a result of a changing combination of exhaust gas recirculation and fuel distribution such that less cylinder-to-cylinder variation is present (e.g. high dilution and low fuel, switched to low dilution and low fuel). Interestingly, despite the reduced cylinder-to-cylinder variation, the results show that the emissions levels are actually not affected. Despite the lack of influence on emissions results, the cylinder-to-cylinder variation in low-temperature combustion modes is still a critical factor that could impact its ability to be implemented in a commercial setting. Further cylinder balancing was attempted and achieved by introducing small (microsecond) adjustments to each cylinder start of injection and injection duration. The balancing is effective, but due to exhaust gas recirculation imbalance, a single adjustment setting does not apply to both conventional and low-temperature combustion modes. Additionally, day-to-day ambient conditions also negate the effectiveness. This supports the idea that some type of consumer-based real-time automatic balancing system may be needed in the future.

Deactivation of a diesel oxidation catalyst due to exhaust species from rich premixed compression ignition combustion in a light-duty diesel engine

Abstract Low-temperature premixed-charge compression ignition (PCI) can significantly reduce both nitric oxide and nitrogen dioxide (NO x ) and particulate matter emissions in compression ignition engines through a range of engine operating conditions. Exhaust hydrocarbons and carbon monoxide can be removed with a diesel oxidation catalyst (DOC). Although PCI normally utilizes a globally fuel-lean mixture, it is independent of equivalence ratio provided that local combustion temperatures are sufficiently low. A more fuel-rich PCI mode of operation could be useful in exhaust after-treatment strategies such as providing carbon monoxide and hydrocarbons for regeneration of a lean NO x trap (LNT). In a previous study, it was found that a rich PCI strategy deactivates a platinum-based DOC within seconds and may allow excessive harmful emissions to be passed into the environment. This study attempts to quantify the effects of different species representative of those found in rich PCI exhaust on a platinum-based DOC in a background of exhaust from an engine operating in a lean PCI regime. Excess carbon monoxide, propane, propylene, and methane were injected in varying concentrations while catalyst outlet temperature, carbon monoxide, and hydrocarbon conversion were measured for a period of 200 s. Of the injected species, it is shown that propylene has the greatest deactivation effect on the catalyst followed by carbon monoxide, both in terms of time and concentration. Propane is found not to deactivate the catalyst even in very globally fuel-rich conditions whereas methane acts as an inert gas over the catalyst in the temperature range of interest. It is concluded from the study that high concentrations of carbon monoxide do not act alone in the poisoning process for the rich PCI condition. The presence of some partial oxidation products such as unsaturated hydrocarbons can also have an adverse effect on DOC performance.

The role of system responses on biodiesel nitric oxide emissions in a medium-duty diesel engine

The often-observed higher emission of nitrogen oxides with biodiesel, relative to petroleum diesel, is well-reported in the literature. Upon review of the literature, there seem to be two broad contributors that cause such a trend: those that are manifested by the effects of fuel property differences directly on in-cylinder processes and those that are manifested by the effects of fuel property differences on engine systems, thus rendering an indirect effect on in-cylinder processes. In this article, the former manifestations are called fundamental issues while the latter manifestations are called system response issues. Both can have significant impact on the magnitude and direction of nitrogen oxides emission differences between biodiesel and petroleum diesel fuels. This article has the objective to identify the distinction between fundamental and system response issues on nitric oxide emissions of biodiesel combustion in a diesel engine. It is noted that the article focuses mostly on the system response issues of a production-type engine, and will only briefly summarize some of the fundamental issues believed to most strongly contribute toward differences in nitric oxide emissions between fuels. Consequently, it is important to note (in fact, a major theme of the article) that many of the specific observations of this study will not necessarily transcend to generality across all engine platforms due to differences in engine technology and calibration; instead, the emphasis on the important role of potential system responses manifested by the use of different fuels of any engine system is meant to be the general contribution of this study. The study generally observes that biodiesel, in the absence of system response issues, emits higher NO x than petroleum diesel. System response issues, however, can have a dramatic impact on biodiesel NO x emissions. In some cases, system response issues may cause biodiesel NO x to be lower than petroleum diesel. Such system response issues highlight potential opportunities to mitigate or decrease biodiesel NO x emissions relative to petroleum diesel.

Investigation Into the Use of Ignition Delay as an Indicator of Low-Temperature Diesel Combustion Attainment

The authors evaluated the attainment of low-temperature diesel combustion in a medium-duty diesel engine apparatus. Attainment of low temperature combustion is determined by the simultaneous and substantial decreases in nitric oxide (NO) and smoke concentrations. The extreme low-temperature combustion condition results in greater than 50% reductions in both NO and smoke concentrations relative to a baseline conventional combustion mode. Combustion development occurs at a low speed (1400 rev/min) and nominally light load (nominally 68 N-m torque, or 1.9 bar brake mean effective pressure). The authors conclude that determination of low-temperature combustion attainment is not universally possible using phenomenologically based ignition delay calculations. Evaluations of two methods to determine start of combustion, which render a definition for ignition delay and for engine ignition delay, reveal that neither provides a consistent metric to determine low-temperature combustion attainment.

Efficiency improvements with low heat rejection concepts applied to diesel low temperature combustion

There is a strong motivation to decrease the production and release of harmful substances such as oxides of nitrogen (NOX) and particulate matter from internal combustion engines. Simultaneously, there are on-going efforts to increase fuel efficiency to curb usage of natural resources and emission of carbon. In general, improvements in one of these areas come at the cost of the other; however, the results of a previous computational study have indicated that emissions can be decreased while simultaneously increasing efficiency through the application of low heat rejection techniques to low temperature combustion. The goal of this study is to experimentally confirm these findings using a light-duty, multi-cylinder diesel engine. Low temperature combustion is realized through high levels of exhaust gas recirculation and retarded injection timings while different degrees of low heat rejection are achieved by means of higher coolant temperatures which should serve to decrease the temperature gradients across the cylinder walls. By applying low heat rejection techniques to diesel low temperature combustion operation, the undesirable side effects of low temperature combustion such as lower combustion and energy conversion efficiencies were found to be mitigated. Specifically, the emissions of carbon monoxide and unburned hydrocarbons were reduced and the loss in fuel conversion efficiency was also diminished. NOX and smoke (an indicator of particulate matter) emissions did increase but they remained at acceptably low levels and below those of conventional combustion. While the full potential of improvements in low temperature combustion was not explored, these results point to the viability of further research into low heat rejection–low temperature combustion concepts.

Biodiesel Effects on Influencing Parameters of Brake Fuel Conversion Efficiency in a Medium Duty Diesel Engine

Biodiesel remains an alternative fuel of interest for use in diesel engines. A common characteristic of biodiesel, relative to petroleum diesel, is a lowered heating value (or per mass energy content of the fuel). For same torque engine comparisons, the lower heating value translates into a higher brake specific fuel consumption (amount of fuel consumed per unit of power produced). The efficiency at which fuel energy converts into work energy, however, may remain unchanged. In this experimental study, evaluating nine unique engine operating conditions, the brake fuel conversion efficiency (an assessor of fuel energy to work energy efficiency) remains unchanged between 100% petroleum diesel fuel and 100% biodiesel fuel (palm olein) at all conditions, except for high load conditions. Several parameters may affect the brake fuel conversion efficiency, including heat loss, mixture properties, pumping work, friction, combustion efficiency, and combustion timing. This article describes a study that evaluates how the aforementioned parameters may change with the use of biodiesel and petroleum diesel, and how these parameters may result in differences in the brake fuel conversion efficiency.

Biodiesel Fuel’s Effects on Influencing Parameters of Brake Fuel Conversion Efficiency in a Medium Duty Diesel Engine

Biodiesel remains an alternative fuel of interest for use in diesel engines. A common characteristic of biodiesel, relative to petroleum diesel, is a lowered heating value (or per mass energy content of the fuel). For same-torque engine comparisons, the lower heating value translates into a higher brake specific fuel consumption (amount of fuel consumed per unit of power produced). The efficiency at which fuel energy converts into work energy, however, may remain unchanged. In this experimental study, evaluating nine unique engine operating conditions, brake fuel conversion efficiency (an assessor of fuel energy to work energy efficiency) remains unchanged between 100% petroleum diesel fuel and 100% biodiesel fuel (palm olein) at all conditions except for high load conditions. Several parameters may affect brake fuel conversion efficiency, including heat loss, mixture properties, pumping work, friction, combustion efficiency, and combustion timing. This article describes a study that evaluates how the aforementioned parameters may change with the use of biodiesel and petroleum diesel, and how these parameters may result in differences in brake fuel conversion efficiency.© 2009 ASME

Particulate Matter Emissions From Late Injection High EGR Low Temperature Diesel Combustion

Low temperature combustion (LTC) is an advanced mode of combustion that has attained much attention due to ever increasing emission standards. LTC simultaneously reduces soot and nitric oxide (NO) emissions by having combustion take place at, for example bulk gas temperatures below 1200K (as observed in this study) so that soot and NO formation is substantially reduced. Soot is typically considered a building block for particulate matter (PM); both PM and NO are heavily regulated emissions by government agencies due to their potential effects on human and environmental health. Although LTC is believed to substantially reduce soot, it is not clear what is the end effect on PM. Because PM is composed of other agents, such as condensed liquid and solid hydrocarbons, there could potentially be non-negligible emission of PM from LTC combustion. This study will compare the gravimetric-based PM data from 3 different modes of combustion in a direct injection diesel engine; specifically: conventional combustion, combustion with high exhaust gas recirculation (EGR) at conventional injection timing, and combustion with high EGR and late injection timing (all other control parameters are the same, including fuel flow rate and engine speed). The objective of this study is to quantify PM emissions of LTC and assess potential differences relative to the soot concentration (the latter as assessed by a smokemeter). PM is gravimetrically measured using a mini-dilution tunnel. Further, chemical analysis of the collected PM is analyzed by an independent laboratory to develop an understanding of the constituent species composing conventional and LTC PM. PM results show that there are differences among the three modes of combustion. The PM differs in appearance as well as composition, and due to the change in appearance FSN may not correlate with PM when running LTC modes of combustion.Copyright

Efficiency Considerations of Later-Phased Low Temperature Diesel Combustion

Low temperature diesel combustion offers an opportunity to simultaneously and substantially reduce exhaust nitrogen oxides and particulate matter emissions. One issue that remains an area of investigation is the improvement of engine efficiency (i.e., specific fuel consumption) for the novel mode of combustion. The objective of this article is to assess the several parameters (i.e., friction, pumping work, combustion phasing, heat transfer rate, and combustion efficiency) that affect the brake fuel conversion efficiencies of a medium-duty diesel engine as its combustion mode is transitioned from conventional to low temperature. The analysis reveals that, in this study’s development of low temperature combustion, late combustion phasing is the primary factor causing a decrease in brake fuel conversion efficiency. To enable low temperature combustion, combustion is retarded to a point where peak rate of heat release occurs at around 24° after top dead center. Such late combustion misses the opportunity to utilize the full expansion stroke of the piston. Although exhaust hydrocarbon and carbon monoxide concentrations increase as a result of the later-phased low temperature combustion mode, combustion efficiency only drops to around 90%. This decrease in combustion efficiency accounts for only about 18.7% of the corresponding decrease in brake fuel conversion efficiency (the balance decrease being caused by the later-phased combustion). Other factors that typically deteriorate brake fuel conversion efficiency (i.e., pumping work, friction, and rate of heat transfer) are all decreased with this study’s development of low temperature combustion. It is important to note that other implementations of low temperature combustion (e.g., advanced timing low temperature combustion) may not necessarily realize the same reductions in brake fuel conversion efficiency, or reductions may not necessarily be caused by the same dominant factors that are observed in this study’s later-phased low temperature combustion mode.Copyright