Progress and recent trends in homogeneous charge compression ignition (HCCI) engines

Conceptual models for partially premixed low-temperature diesel combustion

Fuel design and management for the control of advanced compression-ignition combustion modes

Evolution, challenges and path forward for low temperature combustion engines

Laser-induced incandescence: Particulate diagnostics for combustion, atmospheric, and industrial applications

Previous work has showed that it may be advantageous to use fuels of lower cetane numbers compared to today’s diesel fuels in compression ignition engines The benefits come from the longer ignition delays that these fuels have There is more time available for the fuel and air to mix before combustion starts which is favourable for achieving low emissions of NOx and smoke though premixing usually leads to higher emissions of CO and unburned hydrocarbons In the present work, operation of a single-cylinder lightduty compression ignition engine on four different fuels of different octane numbers, in the gasoline boiling range, is compared to running on a diesel fuel The gasoline fuels have research octane numbers (RON) of 91, 84, 78, and 72 These are compared at a low load/low speed condition (4 bar IMEP / 1200 rpm) in SOI sweeps as well as at a higher load and speeds (10 bar IMEP / 2000 and 3000 rpm) in EGR sweeps There is a NOx advantage for the 91 RON and 84 RON fuels at the lower load At the higher load, NOx levels can be reduced by increasing EGR for all gasolines while maintaining much lower smoke levels compared to the diesel In the conditions studied, the optimum RON range might be between 75 and 85

Fuel Octane Effects in the Partially Premixed Combustion Regime in Compression Ignition Engines

Much of the technology in advanced diesel engines, such as high injection pressures, is aimed at overcoming the short ignition delay of conventional diesel fuels to promote premixed combustion in order to reduce NOx and smoke. Previous work in a 2 l single-cylinder diesel engine with a compression ratio of 14 has demonstrated that gasoline fuel, because of its high ignition delay, is very beneficial for premixed compression-ignition compared with a conventional diesel fuel. We have now done similar studies in a smaller-0.537 l-single-cylinder diesel engine with a compression ratio of 15.8. The engine was run on three fuels of very different auto-ignition quality-a typical European diesel fuel with a cetane number (CN) of 56, a typical European gasoline of 95 RON and 85 MON with an estimated CN of 16 and another gasoline of 84 RON and 78 MON (estimated CN of 21). The previous results with gasoline were obtained only at 1200 rpm-here we compare the fuels also at 2000 rpm and 3000 rpm. At 1200 rpm, at low loads (similar to 4 bars indicated mean effective pressure (IMEP)) when smoke is negligible, NOx levels below 0.4 g/kWh can be easily attained with gasoline without using exhaust gas recirculation (EGR), while this is not possible with the 56 CN European diesel. At these loads, the maximum pressure-rise rate is also significantly lower for gasoline. At 2000 rpm, with 2 bars absolute intake pressure, NOx can be reduced below 0.4 g/kW h with negligible smoke (FSN < 0.1) with gasoline between 10 bars and 12 bars IMEP using sufficient EGR, while this is not possible with the diesel fuel. At 3000 rpm, with the intake pressure at 2.4 bars absolute, NOx of 0.4 g/kW h with negligible smoke was attainable with gasoline at 13 bars IMEP. Hydrocarbon and CO emissions are higher for gasoline and will require after-treatment. High peak heat release rates can be alleviated using multiple injections. Large amounts of gasoline, unlike diesel, can be injected very early in the cycle without causing heat release during the compression stroke and this enables the heat release profile to be shaped. [DOI: 10.1115/1.4000602] (Less)

Low NOx and Low Smoke Operation of a Diesel Engine Using Gasolinelike Fuels

A single-cylinder diesel engine has been run on gasolines of different octane numbers and on model fuels, mixtures of iso-octane, n-heptane and toluene, at different operating conditions. The autoignition quality of the fuel is best described by an Octane Index, OI = (1 - K) . RON + K . MON for fuels in the gasoline autoignition range where RON and MON are, respectively, the Research and Motor Octane numbers and K is an empirical constant which is measured to be negative. Hence for a given RON, a non-paraffinic fuel, of lower MON, will have higher OI and more resistance to autoignition. For a given operating condition, ignition delay increases non-linearly with OI and changes little over the autoignition range of practical diesel fuels. Heat release following the autoignition is influenced by the stratification which will increase as the time between the end of injection and start of combustion decreases and combustion phasing parameters such as Combustion Delay, the difference between the 50% burn time and the start of injection, become less correlated with fuel autoignition quality. Higher ignition delays facilitate premixed combustion in the diesel engine. If two fuels have similar combustion phasing at the same injection timing, their emissions performance is also similar. Hence a good surrogate for gasoline in partially premixed compression ignition engines is a mixture of toluene, iso-octane and n-heptane with the same RON and MON. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved. (Less)

Autoignition quality of gasoline fuels in partially premixed combustion in diesel engines

Some Effects of Fuel Autoignition Quality and Volatility in Premixed Compression Ignition Engines

Simultaneous OH- and formaldehyde LIF measurements have been performed in an HCCI engine using two laser sources working on 283 and 355 nm, respectively. Two ICCD camera systems, equipped with long-pass filters, were used to collect the LIF signals. The simultaneous images of OH and formaldehyde were compared with heat-release calculated from the pressure-trace matching the cycle for the LIF measurements. The measurements were performed on a 0.5-l, single-cylinder optical engine equipped with port-fuel injection system. A blend of iso-octane and n-heptane was used as fuel and the compression ratio was set to 12:1. The width of the laser sheet was 40 mm and hence covered approximately half of the cylinder bore. At some 20 CAD BTDC low temperature reactions are present and formaldehyde is formed. The formaldehyde signal is then rather constant until the main heat-release starts just before TDC, where the signal decreases rapidly to low values. From some 15 CAD to 5 CAD BTDC the formaldehyde is uniformly distributed in the imaged area. As formaldehyde decreases, OH increases and follows the main rate of heat release curve, though with a slight lag in phase. Thereafter OH is formed in the areas from which the formaldehyde has disappeared and the OH signal is present to some 20 CAD ATDC. (Less)

/pdf/simultaneous-oh-and-formaldehyde-lif-measurements-in-an-hcci-51qaxga0rr.pdf

Leif Hildingsson

Papers

Fuel Octane Effects in the Partially Premixed Combustion Regime in Compression Ignition Engines

Low NOx and Low Smoke Operation of a Diesel Engine Using Gasolinelike Fuels

Autoignition quality of gasoline fuels in partially premixed combustion in diesel engines

Some Effects of Fuel Autoignition Quality and Volatility in Premixed Compression Ignition Engines

Simultaneous OH- and Formaldehyde-LIF Measurements in an HCCI Engine