Showing papers in "SAE International Journal of Fuels and Lubricants in 2012"

Dual-Injection as a Knock Mitigation Strategy Using Pure Ethanol and Methanol

Abstract: For spark ignition (SI) engines, the optimum spark timing is crucial for maximum efficiency. However, as the spark timing is advanced, so the propensity to knock increases, thus compromising efficiency. One method to suppress knock is to use high octane fuel additives. However, the blend ratio of these additives cannot be varied on demand. Therefore, with the advent of aggressive downsizing, new knock mitigation techniques are required. Fortuitously, there are two well-known lower alcohols which exhibit attractive knock mitigation properties: ethanol and methanol. Both not only have high octane ratings, but also result in greater charge-cooling than with gasoline. In the current work, the authors have exploited these attractive properties with the dual-injection, or the dual-fuel concept (gasoline in PFI and fuel additive in DI) using pure ethanol and methanol. The single cylinder engine results at 1500 rpm (λ=1) show benefits to indicated efficiency and emissions (HC, CO and CO2) at almost every load (4.5 bar to 8.5 bar IMEP) compared to GDI. This is because the spark timing can be significantly advanced despite the use of relatively low blends (≤50%, by volume), which lowers the combustion duration and improves the conversion of fuel energy into useful work. Overall, these results reinforce the potential of the dual-injection concept to provide a platform for aggressive downsizing, whilst contributing to a renewable energy economy. Copyright © 2012 SAE International.

Soot and Ash Deposition Characteristics at the Catalyst-Substrate Interface and Intra-Layer Interactions in Aged Diesel Particulate Filters Illustrated using Focused Ion Beam (FIB) Milling

Abstract: The accumulation of soot and lubrication-derived ash particles in a diesel particulate filter (DPF) increases exhaust flow restriction and negatively impacts engine efficiency. Previous studies have described the macroscopic phenomenon and general effects of soot and ash accumulation on filter pressure drop. In order to enhance the fundamental understanding, this study utilized a novel apparatus, that of a dual beam scanning electron microscope (SEM) and focused ion beam (FIB), to investigate microscopic details of soot and ash accumulation in the DPF. Specifically, FIB provides a minimally invasive technique to analyze the interactions between the soot, ash, catalyst/washcoat, and DPF substrate with a high degree of measurement resolution. The FIB utilizes a gallium liquid metal ion source which produces Ga+ ions of sufficient momentum to directionally mill away material from the soot, ash, and substrate layers on a nm-μm scale. As the FIB cuts into the sample, uncovering intra-layer details, the coupled high resolution SEM imaging and energy dispersive x-ray (EDX) analysis provide both morphological and chemical data. This tool was applied to investigate soot and ash accumulation in the DPF, with a specific focus on characterizing interactions between the soot/ash/DPF interfaces, such as soot penetration into the ash layer, as well as soot and ash accumulation in the DPF surface pores. In particular, ash and soot particle size, layer pore structure, and the extent of penetration or intra-layer mixing, are all parameters directly impacting DPF pressure drop, which may be quantified using this technique. The work in this study leveraged existing databases of aged DPFs containing various levels of soot and ash, originating from field trials and controlled laboratory testing. Results obtained with this technique provide a fresh and complementary perspective, as well as additional details useful to understand the macroscopic observations of the combined ash and soot effects on diesel particulate filter pressure drop.

Effects of Combustion Phasing, Injection Timing, Relative Air-Fuel Ratio and Variable Valve Timing on SI Engine Performance and Emissions using 2,5-Dimethylfuran

Abstract: Ethanol has long been regarded as the optimal gasoline-alternative biofuel for spark-ignition (SI) engines. It is used widely in Latin and North America and is increasingly accepted as an attractive option across Europe. Nevertheless, its low energy density requires a high rate of manufacture; in areas which are deficient of arable land, such rates might prove problematic. Therefore, fuels with higher calorific values, such as butanol or 2,5-dimethylfuran (DMF) deserve consideration; a similar yield to ethanol, in theory, would require much less land. This report addresses the suitability of DMF, to meet the needs as a biofuel substitute for gasoline in SI engines, using ethanol as the biofuel benchmark. Specific attention is given to the sensitivity of DMF to various engine control parameters: combustion phasing (ignition timing), injection timing, relative air-fuel ratio and valve timing (intake and exhaust). Focus is given to the window for optimization; the parameter range which sustains optimal IMEP (within 2%) but provides the largest reduction of emissions (HC or NOx). The test results using a single cylinder SI research engine at 1500rpm show how DMF is less sensitive to key engine parameters, compared to gasoline. This allows a wider window for emissions optimization because the IMEP remains optimal across a greater parameter range. Copyright © 2012 SAE International.

The effect of the position of oxygen group to the aromatic ring to emission performance in a heavy-duty diesel engine

Abstract: In this paper the soot-NOx trade-off and fuel efficiency of various aromatic oxygenates is investigated in a modern DAF heavy-duty diesel engine. All oxygenates were blended to diesel fuel such that the blend oxygen concentration was 2.59 wt.-%. The oxygenates in question, anisole, benzyl alcohol and 2-phenyl ethanol, have similar heating values and cetane numbers, but differ in the position of the functional oxygen group relative to the aromatic ring. The motivation for this study is that in lignin, a widely available and low-cost biomass feedstock, similar aromatic structures are found with varying position of the oxygen group to the aromatic ring. From the results it becomes clear that both the soot-NOx trade-off and the volumetric fuel economy (i.e. ml/kWh) is improved for all oxygenates in all investigated work points. In general, the improvement in the soot-NOx trade-off correlated with the position of the functional oxygen group to the ring, with better overall emission behavior observed as the oxygen group was further from the ring. No distinct trend was observed with respect to fuel economy