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Finding a replacement for fossil fuels is critical for the future of automotive transportation. The compression ignition (CI) engine is an important aspect of everyday life by means of transportation and shipping of materials. Biodiesel is a viable augmentation for conventional diesel fuel in compression ignition engines. Biodiesel-fuelled diesel engines produce less particulate matter (PM) relative to conventional diesel and biodiesel has the ability to be a carbon dioxide (CO₂) neutral fuel, which may come under government regulation as a greenhouse gas. Although biodiesel is a viable diesel replacement and has certain emissions benefits, it typically also has a known characteristic of higher oxides of nitrogen (NOx) emissions relative to petroleum diesel. Advanced modes of combustion such as low temperature combustion (LTC) have attained much attention due to ever-increasing emission standards, and could also help reduce NOx in biodiesel.

In the wake of global focus shifting towards the health and conservation of the planet, greater importance is placed upon the hazardous emissions of our fossil fuels, as well as their finite supply. These two areas remain intense topics of research in order to reduce greenhouse gas emissions and increase the fuel efficiency of vehicles, a sector which is a major contributor to society's global CO₂ emissions and consumer of fossil-fuel resources. A particular solution to this problem is the diesel engine, with its inherently fuel-lean combustion, which gives rise to low CO₂ production and higher efficiencies than other potential powertrain solutions. Diesel engines, however, typically exhibit higher nitrogen oxides (NOx) and soot engine-out emissions than their gasoline counterparts. NOx is an ingredient to ground-level ozone production and smoke is a possible carcinogen, both of which are facing stricter emissions regulations.

Internal combustion engines have dealt with increasingly restricted emissions requirements. After-treatment devices are successful bringing emissions into compliance, but in-cylinder combustion control can reduce their burden by reducing engine-out emissions. For example, oxides of nitrogen (NOx) are diesel combustion exhaust species of notoriety for their difficulty in after-treatment removal. In-cylinder conditions can be controlled for low levels of NOx, but this produces high levels of soot particulate matter (PM). The simultaneous reduction of NOx and PM can be realized through a combustion process known as low temperature combustion (LTC). This paper presents an investigation into the manifestation of LTC in the calculated heat release profile. Such a study could be important since some extreme LTC conditions may exhibit a return to the soot-NOx tradeoff, rendering an emissions-based definition of LTC unhelpful.

The potential of biodiesel as a viable alternative to petroleum diesel has been driving experimental efforts to insure efficient, high-power, and low emissions operation for many years. Literature is rich with discussion about the differences in operation between biodiesel and petroleum diesel; often, however, these discussions focus on time averaged results that may not detect subtle differences in cycle-to-cycle operation. This aspect has motivated this research study, which compares certain combustion aspects of both fuels on a cycle-by-cycle basis. Thus, the objective of this experimental study is to link fuel property differences between biodiesel and petroleum diesel fuels to potential differences in cycle-to-cycle variability. Steady-state operation of a medium-duty diesel engine at nine different operating conditions, for each fuel, is discussed.

The often-observed differences in nitrogen oxides, or NOx, emissions between biodiesel and petroleum diesel fuels in diesel engines remain intense topics of research. In several instances, biodiesel-fuelled engines have higher NOx emissions than petroleum-fuelled engines; a situation often referred to as the "biodiesel NOx penalty." The literature is rich with investigations that reveal many fundamental mechanisms which contribute to (in varying and often inverse ways) the manifestation of differences in NOx emissions; these mechanisms include, for example, differences in ignition delay, changes to in-cylinder radiation heat transfer, and unequal heating values between the fuels. In addition to fundamental mechanisms, however, are the effects of "system-response" issues.

Due to its ease of use in diesel engines, its presumably lower carbon footprint, and its potential as a renewable fuel, biodiesel has attracted considerable attention in technological development and research literature. Much literature is devoted to evaluating the injection and combustion characteristics of biodiesel fuel using unit injectors, where injection pressure and timing are regulated within the same unit. The use of common rail fuel systems, where fuel pressure is now equally governed to each injector (of a multi-cylinder engine), may change the conventionally accepted impact of biodiesel on injection and combustion characteristics. The objectives of this study are to characterize the responses of an electronically-controlled common-rail fuel injector (in terms of timing and duration) when delivering either 100% palm olein biodiesel or 100% petroleum diesel for a diesel engine, and correlate potential changes in injector characteristics to changes in combustion.