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Technical Paper

An Experimental Investigation of Fischer-Tropsch Fuels in a Light-Duty Diesel Engine

Experiments were performed using a Light-Duty, single-cylinder, research engine in which the emissions, fuel consumption and combustion characteristics of two Fischer-Tropsch (F-T) Diesel fuels derived from natural gas and two conventional Diesel fuels (Swedish low sulfur Diesel and European EN 590 Diesel) were compared. Due to their low aromatic contents combustion with the F-T Diesel fuels resulted in lower soot emissions than combustion with the conventional Diesel fuels. The hydrocarbon emissions were also significantly lower with F-T fuel combustion. Moreover the F-T fuels tended to yield lower CO emissions than the conventional Diesel fuels. The low emissions from the F-T Diesel fuels, and the potential for producing such fuels from biomass, are powerful reason for future interest and research in this field.
Technical Paper

Ion Current Sensing in an Optical HCCI Engine with Negative Valve Overlap

Ion current sensors have high potential utility for obtaining feedback signals directly from the combustion chamber in internal combustion engines. This paper describes experiments performed in a single-cylinder optical engine operated in HCCI mode with negative valve overlap to explore this potential. A high-speed CCD camera was used to visualize the combustion progress in the cylinder, and the photographs obtained were compared with the ion current signals. The optical data indicate that the ions responsible for the chemiluminescence from the HCCI combustion have to be in contact with the sensing electrode for an ion current to start flowing through the measurement circuit. This also means that there will be an offset between the time at which 50% of the fuel mass has burned and 50% of the ion current peak value is reached, which is readily explained by the results presented in the paper.
Technical Paper

Spray Shape and Atomization Quality of an Outward-Opening Piezo Gasoline DI Injector

The spray formation and consequent atomization of an outward opening piezo-electric gasoline DI injector have been experimentally investigated in a constant pressure spray chamber. The sizes and velocities of the droplets and the resulting spray shape were evaluated, under different boundary conditions, using Planar Mie scattering and Planar Laser-induced Fluorescence (PLIF) in combination with Phase Doppler Anemometry (PDA) analyses and high-speed video photography. The use of piezo-electric actuation for gasoline DI injectors provides an additional means to control the atomization and spray shape that is not available with solenoid-driven injectors such as swirling and multi-hole type injectors. For instance, with piezo injectors up to four injections per cycle are possible, and the fuel flow rate can be controlled by adjusting needle lift. The captured high-speed video images show that a hollow-cone spray forms as the fuel exits the outward-opening nozzle.
Technical Paper

Influence of Fuel Parameters on Deposit Formation and Emissions in a Direct Injection Stratified Charge SI Engine

This work investigates the influence of fuel parameters on deposit formation and emissions in a four-cylinder direct injection stratified charge (DISC) SI engine. The engine tested is a commercial DISC engine with a wall-guided combustion system. The combustion chamber deposits (CCDs) were analyzed with gas chromatography / mass spectrometry as well as thickness and mass measurements. Intake valve deposits (IVDs) were analyzed for mass, while internal injector deposits were evaluated using spray photography. The CCD build-up was obtained with the CEC1 F-020-A-98 performance test for evaluation of the influence of fuels and additives on IVDs and CCDs in port fuel injected SI engines. The 60 h test is designed to simulate city driving. Four fuels were compared in the study: a base gasoline, with and without a fuel additive, a specially blended high volatility gasoline, and a fuel representing the worst case of European gasolines; neither of the latter two had additives.
Technical Paper

A Four Stroke Camless Engine, Operated in Homogeneous Charge Compression Ignition Mode with Commercial Gasoline

A single cylinder, naturally aspirated, four-stroke and camless (Otto) engine was operated in homogeneous charge compression ignition (HCCI) mode with commercial gasoline. The valve timing could be adjusted during engine operation, which made it possible to optimize the HCCI engine operation for different speed and load points in the part-load regime of a 5-cylinder 2.4 liter engine. Several tests were made with differing combinations of speed and load conditions, while varying the valve timing and the inlet manifold air pressure. Starting with conventional SI combustion, the negative valve overlap was increased until HCCI combustion was obtained. Then the influences of the equivalence ratio and the exhaust valve opening were investigated. With the engine operating on HCCI combustion, unthrottled and without preheating, the exhaust valve opening, the exhaust valve closing and the intake valve closing were optimized next.
Technical Paper

Heat Release in the End-Gas Prior to Knock in Lean, Rich and Stoichiometric Mixtures With and Without EGR

SI Engine knock is caused by autoignition in the unburnt part of the mixture (end-gas) ahead of the propagating flame. Autoignition of the end-gas occurs when the temperature and pressure exceeds a critical limit when comparatively slow reactions-releasing moderate amounts of heat-transform into ignition and rapid heat release. In this paper the difference in the heat released in the end-gas-by low temperature chemistry-between lean, rich, stochiometric, and stoichiometric mixtures diluted with cooled EGR was examined by measuring the temperature in the end-gas with Dual Broadband Rotational CARS. The measured temperature history was compared with an isentropic temperature calculated from the cylinder pressure trace. The experimentally obtained values for knock onset were compared with results from a two-zone thermodynamic model including detailed chemistry modeling of the end-gas reactions.
Technical Paper

The Effect of Knock on Heat Transfer in SI Engines

Heat transfer to the walls of the combustion chamber is increased by engine knock. In this study the influence of knock onset and knock intensity on the heat flux is investigated by examining over 10 000 individual engine cycles with a varying degree of knock. The heat transfer to the walls was estimated by measuring the combustion chamber wall temperature in an SI engine under knocking conditions. The influence of the air-fuel ratio and the orientation of the oscillating cylinder pressure-relative to the combustion chamber wall-were also investigated. It was found that knock intensities above 0.2 Mpa influenced the heat flux. At knock intensities above 0.6 Mpa, the peak heat flux was 2.5 times higher than for a non-knocking cycle. The direction of the oscillations did not affect the heat transfer.
Technical Paper

Numerical Evaluation of Direct Injection of Urea as NOx Reduction Method for Heavy Duty Diesel Engines

The effect of ammoniac deoxidizing agent (Urea) on the reduction of NOx produced in the Diesel engine was investigated numerically. Urea desolved in water was directly injected into the engine cylinder during the expansion stroke. The NOx deoxidizing process was described using a simplified chemical kinetic model coupled with the comprehensive kinetics of Diesel oil surrogate combustion. If the technology of DWI (Direct Water Injection) with the later injection timing is supposed to be used, the deoxidizing reactants could be delivered in a controlled amount directly into the flame plume zones, where NOx are forming. Numerical simulations for the Isotta Fraschini DI Diesel engine are carried out using the KIVA-3V code, modified to account for the “co-fuel” injection and reaction with combustion products. The results showed that the amount of NOx could be substantially reduced up to 80% with the injection timing and the fraction of Urea in the solution optimized.
Technical Paper

Reduction of Soot Emissions from a Direct Injection Diesel Engine using Water-in-Diesel Emulsion and Microemulsion Fuels

The emissions from a direct injection diesel engine measured according to the ECE R49 13-mode cycle and as a function of exhaust gas recirculation are compared for diesel fuel without water addition, and for water-in-diesel as emulsion and microemulsion. The effect of water addition on the soot emissions was remarkably strong for both the emulsion and microemulsion fuels. The average weighted soot emission values for the 13-mode cycle were 0.0024 and 0.0023 g/kWh for the two most interesting emulsion and microemulsion fuels tested, respectively; 5-fold lower than the US 2007 emission limit.
Technical Paper

Performance of a Heavy Duty DME Diesel Engine - an Experimental Study

Combustion characteristics of dimethyl ether, DME, have been investigated experimentally, in a heavy duty single cylinder engine equipped with an adapted common rail fuel injection system, and the effects of varying injection timing, rail pressure and exhaust gas recirculation on the combustion and emission parameters. The results show that DME combustion does not produce soot and with the use of exhaust gas recirculation NOX emissions can also be reduced to very low levels. However, high injection pressure and/or a DME adopted combustion system is required to improve the mixing process and thus reduce the combustion duration and carbon monoxide emissions.
Technical Paper

Optical study of HCCI Combustion using NVO and an SI Stratified Charge

The effects of using an SI stratified charge in combination with HCCI combustion on combustion phasing, rate of heat release and emissions were investigated in engine experiments to identify ways to extend the operational range of HCCI combustion to lower loads. In the experiments an optical single-cylinder engine equipped with a piezo electric outward-opening injector and operated with negative valve overlap (NVO) and low lift, short duration, camshaft profiles, was used to initiate HCCI combustion by increasing the exhaust gas recirculation (EGR) and thus retaining sufficient thermal energy to reach auto-ignition temperatures. Two series of experiments with full factorial designs were performed, to investigate how the tested parameters (amounts of fuel injected in pilot injections and main injections, stratification injection timing and spark-assistance) influenced the combustion.
Technical Paper

Combustion of Fischer-Tropsch, RME and Conventional Fuels in a Heavy-Duty Diesel Engine

This investigation includes a comparison of two Fischer Tropsch (FT) fuels derived from natural gas and a Rapeseed Methyl Ester (RME) fuel with Swedish low sulfur Diesel in terms of emissions levels, fuel consumption and combustion parameters. The engine used in the study was an AVL single cylinder heavy-duty engine, equipped with a cylinder head of a Volvo D12 engine. Two loads (25% and 100%) were investigated at a constant engine speed of 1200 rpm. The engine was calibrated to operate in different levels of EGR and with variable injections timings. A design of experiments was constructed to investigate the effects of these variables, and to identify optimal settings. The results showed that the soot emissions yielded by FT and RME fuels are up to 40 and 80 percent lower than those yielded by the Swedish Diesel. In addition the FT fuel gave slightly lower, and the RME significant higher NOx emissions than the Swedish Diesel.
Technical Paper

Influence of Ethanol Content in Gasoline on Speciated Emissions from a Direct Injection Stratified Charge SI Engine

The influence of ethanol content in gasoline on speciated emissions from a direct injection stratified charge (DISC) SI engine is assessed. The engine tested is a commercial DISC one that has a wall guided combustion system. The emissions were analyzed using both Fourier transform infrared (FTIR) spectroscopy and conventional emission measurement equipment. Seven fuels were compared in the study. The first range of fuels was of alkylate type, designed to have 0, 5, 10 and 15 % ethanol in gasoline without changing the evaporation curve. European emissions certification fuel was tested, with and without 5 % ethanol, and finally a specially blended high volatility gasoline was also tested. The measurements were conducted at part-load, where the combustion is in stratified mode. The engine used a series engine control unit (ECU) that regulated the fuel injection, ignition and exhaust gas recirculation (EGR).
Technical Paper

Modelling Gasoline Spray-wall Interaction -a Review of Current Models

A literature survey was carried out to examine the advances in knowledge regarding spray impingement on surfaces over the last five years. Published experiments indicate that spray impingement is controlled by various spray parameters, surface conditions, and liquid properties. One disadvantage of the published results is that the experiments have mainly been conducted with water droplets or diesel fuel, often at atmospheric conditions. A sensitivity analysis was performed for one common impingement model. The purpose was to investigate how the model described different phenomena when different parameters were changed, including wall temperature, wall roughness and injection velocity of the spray. The model tested showed sensitivity to surface roughness, whereas changes in wall temperature only resulted in increased evaporation from the surface. The increase of injection velocity resulted in a decrease of fuel on the wall by 70%.
Technical Paper

The Effect of Knock on the Heat Transfer in an SI Engine: Thermal Boundary Layer Investigation using CARS Temperature Measurements and Heat Flux Measurements

It is generally accepted that knocking combustion influences the heat transfer in SI engines. However, the effects of heat transfer on the onset of knock is still not clear due to lack of experimental data of the thermal boundary layer close to the combustion chamber wall. This paper presents measurements of the temperature in the thermal boundary layer under knocking and non-knocking conditions. The temperature was measured using dual-broadband rotational Coherent anti-Stokes Raman Spectroscopy (CARS). Simultaneous time-resolved measurements of the cylinder pressure, at three different locations, and the heat flux to the wall were carried out. Optical access to the region near the combustion chamber wall was achieved by using a horseshoe-shaped combustion chamber with windows installed in the rectangular part of the chamber. This arrangement made CARS temperature measurements close to the wall possible and results are presented in the range 0.1-5 mm from the wall.
Technical Paper

The Effect of Charge Air and Fuel Injection Parameters on Combustion with High Levels of EGR in a HDDI Single Cylinder Diesel Engine

When increasing EGR from low levels to levels corresponding to low temperature combustion, soot emissions first start to increase (due to reductions in soot oxidation), before decreasing to almost zero (due to very low rates of soot formation). At the EGR level where soot emissions start to increase, the NOx emissions are still low, but not low enough to comply with future emission standards. The purpose of this study was therefore to investigate the possibilities for moving the so-called “soot bump” (increase in soot) to higher EGR levels or reducing the magnitude of the soot bump. This involved an experimental investigation of parameters affecting the combustion and thus the engine-out emissions. The parameters investigated were: charge air pressure, injection pressure, EGR temperature and post injection (with different dwell times) for a wide range of EGR rates.
Technical Paper

Experimental and Numerical Investigation of Split Injections at Low Load in an HDDI Diesel Engine Equipped with a Piezo Injector

In order to investigate the effects of split injection on emission formation and engine performance, experiments were carried out using a heavy duty single cylinder diesel engine. Split injections with varied dwell time and start of injection were investigated and compared with single injection cases. In order to isolate the effect of the selected parameters, other variables were kept constant. In this investigation no EGR was used. The engine was equipped with a common rail injection system with a piezo-electric injector. To interpret the observed phenomena, engine CFD simulations using the KIVA-3V code were also made. The results show that reductions in NOx emissions and brake specific fuel consumption were achieved for short dwell times whereas they both were increased when the dwell time was prolonged. No EGR was used so the soot levels were already very low in the cases of single injections.
Technical Paper

Low Temperature Combustion in a Heavy Duty Diesel Engine Using High Levels of EGR

The possibilities for extending the range of engine loads in which soot and NOx emissions can be minimised by using low temperature combustion in conjunction with high levels of EGR was investigated in a series of experiments with a single cylinder research engine. The results show that very low levels of both soot and NOx emissions can be achieved at engine loads up to 50 % by reducing the compression ratio to 14 and applying high levels of EGR (up to approximately 60 %). Unfortunately, the low temperature combustion is accompanied by increases in fuel consumption and emissions of both HC and CO. However, these drawbacks can be reduced by advancing the injection timing. The research engine was a 2 litre direct injected (DI), supercharged, heavy duty, single cylinder diesel engine with a geometry based on Volvo's 12 litre engine, and the amount of EGR was increased by adjusting the exhaust back pressure while keeping the charge air pressure constant.
Technical Paper

Low Soot, Low NOx in a Heavy Duty Diesel Engine Using High Levels of EGR

The objective of the study presented here was to examine the possibility of simultaneously reducing soot and nitrogen oxide (NOx) emissions from a heavy duty diesel engine, using very high levels of EGR (exhaust gas recirculation). The investigation was carried out using a 2 litre DI single cylinder diesel engine. Two different EGR strategies were examined. One entailed maintaining a constant charge air pressure with a varied exhaust back pressure in order to change the amount of EGR. In the other strategy a constant pressure difference was maintained over the engine, resulting in different equivalence ratios at similar EGR levels. EGR levels of 60 % or more significantly reduced both soot and NOx emissions at 25 % engine load with constant charge air pressure and increasing exhaust back pressure. However, combustion under these conditions was incomplete, resulting in high emissions of carbon monoxide (CO), unburned hydrocarbons (HC) and high fuel consumption.
Technical Paper

HCCI Operation of a Passenger Car Common Rail DI Diesel Engine With Early Injection of Conventional Diesel Fuel

The possibilities of operating a direct injection Diesel engine in HCCI combustion mode with early injection of conventional Diesel fuel were investigated. In order to properly phase the combustion process in the cycle and to prevent knock, the geometric compression ratio was reduced from 17.0:1 to 13.4:1 or 11.5:1. Further control of the phasing and combustion rate was achieved with high rates of cooled EGR. The engine used for the experiments was a single cylinder version of a modern passenger car type common rail engine with a displacement of 480 cc. An injector with a small included angle was used to prevent interaction of the spray and the cylinder liner. In order to create a homogeneous mixture, the fuel was injected by multiple short injections during the compression stroke. The low knock resistance of the Diesel fuel limited the operating conditions to low loads. Compared to conventional Diesel combustion, the NOx emissions were dramatically reduced.