William Cannella

Effects of Ethanol and Different Type of Gasoline Fuels on Partially Premixed Combustion from Low to High Load

The behavior of Ethanol and seven fuels in the boiling point range of gasoline but with an Octane Number spanning from 69 to 99 was investigated in Partially Premixed Combustion. A load sweep was performed from 5 to 18 bar gross IMEP at 1300 rpm. The engine used in the experiments was a single cylinder Scania D12. To allow high load operations and achieve sufficient mixing, the compression ratio was decreased from the standard 18:1 to 14.3:1. It was shown that by using only 50% of EGR it is possible to achieve NOx below 0.30 g/kWh even at high loads. At 18 bar IMEP soot was in the range of 1-2 FSN for the gasoline fuels while it was below 0.06 FSN with Ethanol. The use of high boost combined with relatively short combustion duration allowed reaching gross indicated efficiencies in the range of 54 - 56%. At high load the partial stratified mixture allowed to keep the maximum pressure rise rate below 15 bar/CAD with most of the fuels. The brake parameters were estimated and it was found that brake NOx can be far below the EU VI target value and the brake efficiency higher than 48.5 %. According to emissions and efficiency considerations the fuels were classified and it was found that with this specific compression ratio the most suitable fuel for this combustion concept has to have a RON slightly below 90. (Less)

An Advanced Internal Combustion Engine Concept for Low Emissions and High Efficiency from Idle to Max Load Using Gasoline Partially Premixed Combustion

A Scania 13 1 engine modified for single cylinder operations was run using nine fuels in the boiling point range of gasoline, but very different octane number, together with PRF20 and MK1-diesel. The eleven fuels were tested in a load sweep between 5 and 26 bar gross IMEP at 1250 rpm and also at idle (2.5 bar IMEP, 600 rpm). The boost level was proportional to the load while the inlet temperature was held constant at 303 K. For each fuel the load sweep was terminated if the ignitibility limit was reached. A lower load limit of 15 and 10 bar gross IMEP was found with fuels having an octane number range of 93-100 and 80-89 respectively, while fuels with an octane number below 70 were able to run through the whole load range including idle. A careful selection of boost pressure and EGR in the previously specified load range allowed achieving a gross indicated efficiency between 52 and 55% while NOx ranged between 0.1 and 0.5 g/kWh. At high load, in the worst case, the nine gasolines showed 0.5 FSN of soot while diesel showed 2.8 FSN. In the paper it is shown that chemical reasons, rather than mixing, are behind this substantial gap. With the two best fuels, the brake parameters were estimated. It was found that soot was low, and in some cases below both the EU VI and US10 regulations. NOx was always below EU VI, and in some cases was only slight above US10 regulations. At high loads the estimated brake efficiency was roughly 50% in both cases. All the results were achieved keeping the maximum pressure rise rate within acceptable levels. (Less)

Effects of Different Type of Gasoline Fuels on Heavy Duty Partially Premixed Combustion

The effects of fuel properties on the performance and emissions of an engine running in partially premixed combustion mode were investigated using nine test fuels developed in the gasoline boiling point range. The fuels covered a broad range of ignition quality and fuel chemistry.The fuels were characterized by performing a load sweep between 1 and 12 bar gross IMEP at 1000 and 1300 rpm. A heavy duty single cylinder engine from Scania was used for the experiments; the piston was not modified thus resulting in the standard compression ratio of 18:1.In order to properly run gasoline type of fuels in partially premixed combustion mode, an advanced combustion concept was developed. The concept involved using a lot of EGR, very high boost and an advanced injection strategy previously developed by the authors.By applying this concept all the fuels showed gross indicated efficiencies higher than 50% with a peak of 57% at 8 bar IMEP. NOx were mostly below 0.40 g/kWh only in few operative points 0.50 g/kWh was reached. At high load the soot levels were mostly a function of the octane number; with RON higher than 95 it was possible to be below 0.5 FSN while for the more reactive fuels a peak value of 3 FSN was reached at 13 bar IMEP.The pressure rise rate reached a peak of 19 bar/CAD with fuels which had a RON above 95, when the octane number decreased below 90 the pressure rise rate was always below 14 bar/CAD. (Less)

Gasoline partially premixed combustion, the future of internal combustion engines?

Gasoline partially premixed combustion showed the potential of very high efficiency, emissions of nitrogen oxides (NO x ) and soot below future emission regulations, and acceptable acoustic noise from idle up to 26 bar gross indicated mean effective pressure. For instance, gross indicated efficiencies in the range of 53 to 55 per cent were achieved in the whole load range keeping NO x below 0.30 g/kWh, soot below 0.30 filter smoke number (FSN), and relative maximum pressure rise rate below 8 bar/crank angle degree. The goal was achieved by developing an appropriate EGR–λ (exhaust gas recirculation/relative excess of air) combination and an advanced injection strategy, and by making minor modifications to the engine layout. The current paper presents a summary of the advantages of using gasoline-type fuels (research octane number (RON) from 80 to 69) in a heavy-duty compression ignition engine. Low-octane-number gasoline fuels were chosen because they can run from idle to maximum load without any major modification to the engine layout and because low-load operations are achievable even when the engine is cold and the inlet temperature is low. Experiments were carried out in two single-cylinder engines, Scania D12 and Scania D13, using a total of three different engine setups. The influence of different types of gasoline (RON from 99 to 69) on this novel combustion concept was analysed. A comparison between gasoline and diesel fuels is presented and the viability of reaching 50 per cent brake efficiency while keeping low emissions of NO x and soot is shown.

Influence of Inlet Pressure, EGR, Combustion Phasing, Speed and Pilot Ratio on High Load Gasoline Partially Premixed Combustion

The current research focuses in understanding how inlet pressure, EGR, combustion phasing, engine speed and pilot main ratio are affecting the main parameters of the combustion (e.g. efficiency, NOx, soot, maximum pressure rise rate) in the novel concept of injecting high octane number fuels in partially premixed combustion. The influence of the above mentioned parameters was studied by performing detailed sweeps at 32 bar fuel MEP (c.a. 16-18 bar gross IMEP); three different kinds of gasoline were tested (RON: 99, 89 and 69). The experiments were ran in a single cylinder heavy duty engine; Scania D12. At the end of these sweeps the optimized settings were computed in order to understand how to achieve high efficiency, low emissions and acceptable maximum pressure rise rate. The least square optimization analysis showed that for all the three fuels at this load it is possible to achieve gross indicated efficiency higher than 54 %, maximum pressure rise rate below 15 bar/CAD, NOx below 0.25 g/kWh and soot below 1.50 FSN. Depending on the fuel type, the targets were achieved by using 46-52 % of EGR, single injection, combustion phasing between 2 and 4 TDC and lambda between 1.54 and 1.58. (Less)

Partial Fuel Stratification to Control HCCI Heat Release Rates: Fuel Composition and Other Factors Affecting Pre-Ignition Reactions of Two-Stage Ignition Fuels

Homogeneous charge compression ignition (HCCI) combustion with fully premixed charge is severely limited at high-load operation due to the rapid pressure-rise rates (PRR) which can lead to engine knock and potential engine damage. Recent studies have shown that two-stage ignition fuels possess a significant potential to reduce the combustion heat release rate, thus enabling higher load without knock.

Predicting Fuel Performance for Future HCCI Engines

The purpose of this research is to investigate the impact of fuel composition on auto-ignition in homogeneous charge compression ignition (HCCI) engines in order to develop a future metric for predicting fuel performance in future HCCI engine technology. A single-cylinder, variable compression ratio engine operating as an HCCI engine was used to test reference fuels and gasoline blends with octane numbers (ON) ranging from 60 to 88. Correlations between fuel composition, ON, and two existing methods for predicting fuel auto-ignition in HCCI engines (Kalghatgis octane index and Shibata and Urushiharas HCCI index) are investigated. Results show that octane index and HCCI index poorly predict the impact of fuel composition on auto-ignition for fuels with the same ON. The effect of ethanol in delaying auto-ignition depends on the composition of the original gasoline blend; the same is true for the addition of naphthenes. Low-temperature heat release (LTHR) correlates well with auto-ignition for gasoline fuels exhibiting LTHR.

Fuels for Advanced Combustion Engines Research Diesel Fuels: Analysis of Physical and Chemical Properties

The CRC Fuels for Advanced Combustion Engines working group has worked to identify a matrix of research diesel fuels for use in advanced combustion research applications. Nine fuels were specified and formulated to investigate the effects of cetane number aromatic content and 90% distillation fraction. Standard ASTM analyses were performed on the fuels as well as GC/MS and /u1H//u1/u3C NMR analyses and thermodynamic characterizations. Details of the actual results of the fuel formulations compared with the design values are presented, as well as results from standard analyses, such as heating value, viscosity and density. Cetane number characterizations were accomplished by using both the engine method and the Ignition Quality Tester (IQT/sT) apparatus.

Effects of refinery stream gasoline property variation on the auto-ignition quality of a fuel and homogeneous charge compression ignition combustion

The combination of in-cylinder thermal environment and fuel ignition properties plays a critical role in the homogeneous charge compression ignition engine combustion process. The properties of fuels available in the automotive market vary considerably and display different auto-ignition behaviors for the same intake charge conditions. Thus, in order for homogeneous charge compression ignition (HCCI) technology to become practically viable, it is necessary to characterize the impact of differences in fuel properties as a source of ignition/combustion variability. To quantify the differences, 15 gasolines composed of blends made from refinery streams were investigated in a single-cylinder homogeneous charge compression ignition engine. The properties of the refinery stream blends were varied according to research octane number, sensitivity (S = research octane number − motor octane number) and volumetric contents of aromatics and olefins. Nine fuels contained 10% ethanol by volume, and six more were blended with 20% ethanol. Pure ethanol (E100) and an un-oxygenated baseline fuel (RD3-87) were included too. For each fuel, a sweep of intake temperature at a consistent load and engine speed was conducted, and the combustion phasing given by the crank angle of 50% mass fraction burned was tracked to assess the sensitivity of auto-ignition to fuel chemical kinetics. The experimental results provided a wealth of information for predicting the HCCI combustion phasing from the given properties of a fuel. In this study, the original octane index correlation proposed by Kalghatgi based solely on fuel research octane number and motor octane number was found to be insufficient for characterizing homogeneous charge compression ignition combustion of refinery stream fuels. A new correlation was developed for estimation of auto-ignition properties of practical fuels in the typical HCCI engine. Fuel composition, captured by terms indicating the fraction of aromatics, olefins, saturates and ethanol, was added to generate the following formula: O I JKZ = RON − K ′ · S + κ · ( Aromatic s 2 ) ( Olefins + Saturates ) + ε · ( Aromatics · Ethanol ) . The results indicate a significantly improved estimation of combustion phasing for gasoline fuels of varying chemical composition under low-temperature combustion conditions. Quantitative findings of this investigation and the new octane index correlation can be used for designing robust HCCI control strategies, capable of handling the wide spectrum of fuel chemical compositions found in pump gasoline.

Multi Cylinder Partially Premixed Combustion Performance Using Commercial Light-Duty Engine Hardware

This work investigates the performance potential of an engine running with partially premixed combustion (PPC) using commercial diesel engine hardware. The engine was a 2.01 SAAB (GM) VGT turbocharged diesel engine and three different fuels were run - RON 70 gasoline, RON 95 Gasoline and MK1 diesel. With the standard hardware an operating range for PPC from idle at 1000 rpm up to a peak load of 1000 kPa IMEPnet at 3000 rpm while maintaining a peak pressure rise rate (PPRR) below 7 bar/CAD was possible with either RON 70 gasoline and MK1 diesel. Relaxing the PPRR requirements, a peak load of 1800 kPa was possible, limited by the standard boosting system. With RON 95 gasoline it was not possible to operate the engine below 400 kPa. Low pressure EGR routing was beneficial for efficiency and combined with a split injection strategy using the maximum possible injection pressure of 1450 bar a peak gross indicated efficiency of above 51% was recorded. The split injection strategy showed in general higher efficiency and did lead to noticeable smoother engine operation with a reduction of combustion noise. However, soot emissions did increase strongly when the time between injections was reduced.Compared to conventional diesel combustion, CDC, higher efficiency combined with low NOx and soot operation could be realized with gasoline PPC. Typically, soot levels were two orders of magnitude lower than for CDC. The injection pressure showed an unexpectedly strong correlation with efficiency. Idle operation was realized by closing the VGT and thus increasing the amount of trapped residual gases. Increasing swirl did not lead to any improvements but rather the opposite in terms of fuel consumption and NOx.The standard VGT was a limiting factor and pumping losses typically meant that the net indicated efficiency was limited to slightly above 45%. The results indicate, however, that a simple PPC engine using standard diesel hardware with the addition of LP-EGR and using RON 70 gasoline could be an interesting option trading off some efficiency for complexity and hardware cost. (Less)