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ABSTRACTThe combustion of straight vegetable oil (SVO) in internal combustion engines has shown conflicting results in emissions, power, and engine longevity. Many early studies suggested that SVO should not be considered for long term use in diesel engines. However, waste vegetable oil has been fueling adapted vehicles in progressive communities for years. The issues involved in the combustion of SVO or pure plant oils are complex. Engine injection systems, oil type, lipid acid ratio, and fuel temperature all have significant impact on the engine performance and emissions. A review of published studies of SVO combustion with a focus on known SVO composition and chemical structure reveals trends which merit further study. Future engine tests with known vegetable oil profiles will add significantly to the progression of SVO use in engines.
Water requirements throughout the electricity generation life cycle have important implications for the electricity sector. Thermoelectric power plant operations are estimated as responsible for around 36% [1] to 41% [2] of total freshwater withdrawals in the United States and 3% of total freshwater consumption [1,3]. However, the life cycle of electricity generation consists of many stages besides power plant operation, including component manufacturing, fuel acquisition, processing, and transport, and power plant decommissioning. The water requirements associated with choices along this life cycle, such as the selection of fuel type or cooling technology, are not well understood.
Straight Vegetable Oil (SVO) is a promising biofuel with a low energy input to energy output ratio. Successful use of SVO in engines depends on engine performance, wear and emissions. This study focuses on short-term engine emissions and performance. The primary objective is to compare engine efficiency and emissions from SVO, biodiesel, and petroleum diesel using vegetable oil from four locally produced oilseed species. This research uses oils produced in Colorado as a full diesel fuel substitute in a modified single cylinder engine. This engine testing was conducted in the laboratory. The test engine was a Yanmar TF140E, which is naturally aspirated and uses low-pressure (∼140 bar) mechanical direct injection. The engine fuel system was modified to accommodate a 2-tank custom SVO kit. The SVO was heated to 75˚C. Fuel economy and emissions measurements were performed for petroleum diesel, four different vegetable oils (sunflower, canola, camelina, and soybean) and their biodiesel derivatives. Fuel mass flow, oxides of nitrogen (NOx), total hydrocarbons (THC), carbon monoxide (CO), and particulate matter were measured. Overall engine emissions for SVO and biodiesel, with the exception of THC for biodiesel, were higher than petroleum diesel. More favorable biofuel emissions comparisons to diesel are expected with other engine designs based on data from various literature sources. Data comparing raw and refined SVO indicate that refined vegetable oil produces lower Particulate Matter (PM) emissions. General trends were observed showing that oils with higher levels of polyunsaturated fats (e.g. C18:1, C18:2, and C18:3) produce higher levels of NOx and THC's.
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