Auto-Ignition Quality of Practical Fuels and Implications for Fuel Requirements of Future SI and HCCI Engines

Design and Simulation of Two-Stroke Engines is a unique hands-on information source. The author, having designed and developed many two-stroke engines, offers practical and empirical assistance to the engine designer on many topics ranging from porting layout, to combustion chamber profile, to tuned exhaust pipes. The information presented extends from the most fundamental theory to pragmatic design, development, and experimental testing issues.

Design and Simulation of Two-Stroke Engines

We assessed the emissions response of a fleet of seven light-duty gasoline vehicles for gasoline fuel aromatic content while operating over the LA92 driving cycle. The test fleet consisted of model year 2012 vehicles equipped with spark-ignition (SI) and either port fuel injection (PFI) or direct injection (DI) technology. Three gasoline fuels were blended to meet a range of total aromatics targets (15%, 25%, and 35% by volume) while holding other fuel properties relatively constant within specified ranges, and a fourth fuel was formulated to meet a 35% by volume total aromatics target but with a higher octane number. Our results showed statistically significant increases in carbon monoxide, nonmethane hydrocarbon, particulate matter (PM) mass, particle number, and black carbon emissions with increasing aromatics content for all seven vehicles tested. Only one vehicle showed a statistically significant increase in total hydrocarbon emissions. The monoaromatic hydrocarbon species that were evaluated showed...

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Evaluating the Effects of Aromatics Content in Gasoline on Gaseous and Particulate Matter Emissions from SI-PFI and SIDI Vehicles.

Deposits, derived primarily from the fuel but with some contribution from the oil are formed inside the combustion chamber of a spark-ignition engine with use. The growth of combustion chamber deposits (CCD) is a dynamic and, to an extent, reversible process which at any given time reflects the balance between the formation and removal processes. Engine surface temperature is the most important parameter that affects their formation and changes in engine operation which tend to increase surface temperature, reduce deposit growth. At a fixed temperature, less volatile fuels tend to form more deposits than more volatile fuels. Some detergent additive packages tend to increase CCD levels. CCD reduce the heat lost to the coolant and increase charge temperature thereby increasing flame propagation rates but reducing volumetric efficiency; they might also affect the final phase of combustion by as yet undefined chemical means. This is reflected as an increase in octane requirement and NOx and a reduction in maximum power but an improvement in fuel economy and a reduction in CO2 emissions. They might also lead to higher HC emissions but not necessarily always since there might be competing mechanisms which come into play. CCD effect on CO emissions is not clearly established. They can also cause other interference problems like carbon rap. It is not known to what extent engine performance is affected by small changes in CCD levels. There is a large variation in deposit growth and its response to changes in fuel, additives and engine operating conditions across the combustion chamber and between different engines. Similarly, the performance of different engines will be affected to different extents by the deposits. While assessing the effects of different fuels or additives on engine performance and emissions through their effects on CCD, the simultaneous effects on other aspects such as inlet valve deposits which might have their own effects on engine operation, should also be considered. The paper reviews the literature on these topics.

Combustion Chamber Deposits in Spark-Ignition Engines: A Literature Review

Fuel Effects on Knock in a Highly Boosted Direct Injection Spark Ignition Engine

Studies of Knock in a Spark Ignition Engine with “CARS” Temperature Measurements and Using Different Fuels

Vehicle-based studies have shown that a reduction in the aromatic content of gasoline fuels can result in increased NOx emissions from catalyst-equipped vehicles. A study with simulated exhaust gas has shown that light paraffins, especially methane, are unreactive and cause substantial breakthrough of unreacted NO over the catalyst. However, unsaturated exhaust components including aromatics are effective reactants and play a large part in converting NO over the catalyst. Engine tests have shown that methane is predominantly produced by fuel paraffins and olefins, but hardly at all by aromatics. Thus it appears that methane generated during combustion of low aromatics fuels may be the cause, wholly or in part, of the poor NO conversion efficiency observed when catalyst-equipped cars are operated on such fuels. However, it cannot be excluded that low aromatics fuels are associated with increased air-to-fuel ratio which will also contribute to poor NO performance.

The influence of the fuel hydrocarbon composition on no conversion in 3-way catalysts : the nox/aromatics effect

The independent effects of fuel aromatic content and mid-range volatility on tailpipe emissions from current technology european vehicle fleets

A road test has been conducted to quantify the benefits provided by a high-performance gasoline additive package in a fleet of cars representative of Europe, SE Asia, and South America. The emissions, fuel consumption, and engine cleanliness benefits of additised versus untreated gasoline were compared in 15 pairs of cars. A further 6 cars were operated on a mixture of fuels to show the benefits of additised fuel versus mixed fuelling. The design of the experiment was based on a similar road test conducted in 1991. Through careful test design and execution, it has been possible to assess the performance of the package at a high statistical confidence level. The package provides a high level of inlet system cleanliness, a significant reduction in fuel consumption and reduced HC emissions.

C. R. McDonald

Papers

Studies of Knock in a Spark Ignition Engine with “CARS” Temperature Measurements and Using Different Fuels

The influence of the fuel hydrocarbon composition on no conversion in 3-way catalysts : the nox/aromatics effect

The independent effects of fuel aromatic content and mid-range volatility on tailpipe emissions from current technology european vehicle fleets

A Critical Road Test Evaluation of a High-Performance Gasoline Additive Package in a Fleet of Modern European and Asian Vehicles

The Role of Methane on Catalyst Conversion of NOx: A Study Based on FTIR