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Lean-burn combustion is an effective method for increasing the thermal efficiency of gasoline engines fueled with stoichiometric fuel-air mixture, but leads to an unacceptable level of high cyclic variability before reaching ultra-low nitrogen oxide (NOx) emissions emitted from conventional gasoline engines. Multi-point micro-flame ignited (MFI) hybrid combustion was proposed to overcome this problem, and can be can be grouped into double-peak type, ramp type and trapezoid type with very low frequency of appearance. This research investigates the micro-flame ignition stages of double-peak type and ramp type MFI combustion captured by high speed photography. The results show that large flame is formed by the fast propagation of multi-point flame occurring in the central zone of the cylinder in the double-peak type. However, the multiple flame sites occur around the cylinder, and then gradually propagate and form a large flame accelerated by the independent small flame in the ramp type.

A multi-cycle three-dimensional CFD engine simulation programme has been developed and applied to analyze the Controlled autoignition (CAI) combustion, also known as homogeneous charge compression ignition (HCCI), in a direct injection gasoline engine. CAI operation was achieved through the negative valve overlap method by means of a set of low lift camshafts. The effect of single injection timing on combustion phasing and underlying physical and chemical processes involved was examined through a series of analytical studies using the multi-cycle 3D engine simulation programme. The analyses showed that early injection into the trapped burned gases of a lean-burn mixture during the negative valve overlap period had a large effect on combustion phasing, due to localized heat release and the production of chemically reactive species. As the injection was retarded to the intake stroke, the charge cooling effect tended to slow down the autoignition process.

A fuel stratification concept has been developed in a three-valve twin-spark spark ignition engine. This concept requires that two fuels or fuel components of different octane numbers (ON) be introduced into the cylinder separately through two independent inlet ports. They are then stratified into two regions laterally by a strong tumbling flow and ignited by the spark plug located in each region. This engine can operate in the traditional stratified lean-burn mode at part loads to obtain a good part-load fuel economy as long as one fuel is supplied. At high loads, an improved fuel economy might also be obtained by igniting the low ON fuel first and leaving the high ON fuel in the end gas region to resist knock. This paper gives a detailed description of developing the fuel stratification concept, including optimization of in-cylinder flow, mixture and combustion.

CAI combustion has the potential to be the most clean combustion technology in internal combustion engines and is being intensively researched. Following the previous research on CAI combustion of gasoline fuel, systematic investigation is being carried out on the application of bio-fuels in CAI combustion. As part of an on-going research project, CAI combustion of methanol and ethanol was studied on a single-cylinder direct gasoline engine with an air-assisted injector. The CAI combustion was achieved by trapping part of burnt gas within the cylinder through using short-duration camshafts and early closure of the exhaust valves. During the experiment the engine speed was varied from 1200rpm to 2100rpm and the air/fuel ratio was altered from the stoichiometry to the misfire limit. Their combustion characteristics were obtained by analysing cylinder pressure trace.

In order to take advantage of different properties of fuel components or fractions, a new concept of fuel stratification has been proposed by the authors. This concept requires that two fractions of standard gasoline (e.g., light and heavy fractions) or two different fuels in a specially formulated composite be introduced into the cylinder separately through two separate intake ports. The two fuels will be stratified into two regions in the cylinder by means of strong tumble flows. In order to verify and optimize the fuel stratification, a two-tracer Laser Induced Fluorescence (LIF) technique was developed and applied to visualize fuel stratification in a three-valve twin-spark SI engine. This was realized by detecting simultaneously fluorescence emissions from 3-pentanone in one fuel (hexane) and from N,N-dimethylaniline (DMA) in the other fuel (iso-octane).

In-cylinder flow was optimised in a three-valve twin-spark-plug SI engine in order to obtain good two-zone fuel fraction stratification in the cylinder by means of tumble flow. First, the in-cylinder flow field of the original intake system was measured by Particle Image Velocimetry (PIV). The results showed that the original intake system did not produce large-scale in-cylinder flow and the velocity value was very low. Therefore, some modifications were applied to the intake system in order to generate the required tumble flow. The modified systems were then tested on a steady flow rig. The results showed that the method of shrouding the lower part of the intake valves could produce rather higher tumble flow with less loss of the flow coefficient than other methods. The optimised intake system was then consisted of two shroud plates on the intake valves with 120° angles and 10mm height. The in-cylinder flow of the optimised intake system was investigated by PIV measurements.

An experimental test of a non-contact method for determining simultaneously the pressure in each cylinder of a reciprocating engine is reported. The method exploits a pattern recognition technique to compare crankshaft speed fluctuations to reference patterns in a knowledge base. The crankshaft speed is measured by timing the passage of gear teeth on the engine's flywheel. The experiment was carried out on a Detroit Diesel Corporation 6V-92TA engine. The baseline operating condition was 75 percent rated load at 1200 rpm. The engine's six cylinders were individually under-fuelled from the baseline operating condition to achieve peak pressure reductions of 5 to 20 percent. The required reference angular velocity waveforms were obtained by measuring the effect of under-fuelling individual cylinders to reduce their peak pressures by 10 percent. The experimental results show that the method evaluates the cylinder pressures with an RMS error of less than 6 percent.

The loss mechanisms associated with engine downsizing, boosting and compression ratio change are assessed. Of interest are the extents of friction loss, pumping loss, and crevice loss. The latter does not scale proportionally with engine size. These losses are deconstructed via a cycle simulation model which encompasses a friction model and a crevice loss model for engine displacement of 300 to 500 cc per cylinder. Boost pressure is adjusted to yield constant torque. The compression ratio is varied from 8 to 20. Under part load, moderate speed condition (1600 rpm; 13.4 Nm/cylinder brake torque), the pumping work reduces significantly with downsizing while the work loss associated with the crevice volume increases. At full load (1600 rpm; 43.6 Nm/cylinder brake torque), the pumping work is less significant. The crevice loss (normalized to the fuel energy) is essentially the same as in the part load case. The sensitivities of the respective loss terms to downsizing are reported.

Direct injection gasoline engines have the potential for improved fuel economy through principally the engine down-sizing, stratified charge combustion, and Controlled Auto Ignition (CAI). However, due to the limited time available for complete fuel evaporation and the mixing of fuel and air mixture, locally fuel rich mixture or even liquid fuel can be present during the combustion process of a direct injection gasoline engine. This can result in significant increase in UHC, CO and Particulate Matter (PM) emissions from direct injection gasoline engines which are of major concerns because of the environmental and health implications. In order to investigate and develop a more efficient DI gasoline engine, a camless single cylinder DI gasoline engine has been developed. Fully flexible electro-hydraulically controlled valve train was used to achieve spark ignition (SI) and Controlled Autoignition (CAI) combustion in both 4-stroke and 2-stroke cycles.

An accurate prediction of residual burned gas within the combustion chamber is important to quantify for development of modern engines, especially so for those with internally recycled burned gases and HCCI operations. A wall-guided GDI engine has been fitted with an in-cylinder sampling probe attached to a fast response NDIR analyser to measure in-situ the cycle-by-cycle trapped residual gas. The results have been compared with a model which predicts the trapped residual gas fraction based on heat release rate calculated from the cylinder pressure data and other factors. The inlet and exhaust valve timings were varied to produce a range of Residual Gas Fraction (RGF) conditions and the results were compared between the actual measured CO2 values and those predicted by the model, which shows that the RGF value derived from the exhaust gas temperature and pressure measurement at EVC is consistently overestimated by 5% over those based on the CO2 concentrations.

In this paper, an experimental study was performed to investigate characteristics of flame propagation and knocking combustion of hydrous (10% water content) and anhydrous ethanol at different air/fuel ratios in comparison to RON95 gasoline. Experiments were conducted in a full bore overhead optical access single cylinder port-fuel injection spark-ignition engine. High speed images of total chemiluminescence and OH* emission was recorded together with the in-cylinder pressure, from which the heat release data were derived. The results show that under the stoichiometric condition anhydrous ethanol and wet ethanol with 10% water (E90W10) generated higher IMEP with at an ignition timing slightly retarded from MBT than the gasoline fuel for a fixed throttle position. Under rich and stoichiometric conditions, the knock limited spark timing occurred at 35 CA BTDC whereas both ethanol and E90W10 were free from knocking combustion at the same operating condition.

A model which converts flame arrival times at a head gasket ionization probe, used in a spark-ignition engine, into flame contours has been developed. The head gasket was manufactured at MIT using printed circuit board techniques. It has eight electrodes symmetrically spaced around the circumference (top of cylinder liner) and it replaces the conventional head gasket. The model is based on engine flame propagation rate data taken from the literature. Data from optical studies of S.I. engine combustion or studies utilizing optical fiber or ionization probe diagnostics were analyzed in terms of the apparent flame speed and the entrainment speed (flame speed relative to the fluid ahead of the flame). This gives a scaling relationship between the flame speed and the mass fraction burned which is generic and independent of the chamber shape.

This paper presents the simulation study on the effects of mechanical turbo-compounding on a turbocharged diesel engine. A downstream power-turbine has been coupled to the exhaust manifold after the main turbocharger, in the aim to recover waste heat energy. The engine in the current study is Scania DC13-06, which 6 cylinders and 13 litre in capacity. The possibilities, effectiveness and working range of the turbo compounded system were analyzed in this study. The system was modeled in AVL BOOST, which is a one dimensional (1D) engine code. The current study found that turbo compounding could possibly recover on average 11.4% more exhaust energy or extra 3.7kW of power. If the system is mechanically coupled to the engine, it could increase the average engine power by up to 1.2% and improve average BSFC by 1.9%.

CAI-combustion was achieved in a 4-cylinder four-stroke gasoline DI engine, with all cylinders running in CAI-mode. Standard components were used, with the exception of the camshafts which had been modified in order to restrict the gas exchange process. Results shown in the paper are between a load of 1.45 - 2.65 bar, an engine speed of 1500rpm and at a lambda value of 1.2. As is typical with this type of combustion, reductions in emissions of NOx were recorded as well as a slight decrease in HC emissions, also there was a reduction in the brake specific fuel consumption. The effect that injection timing on factors such as start of combustion, combustion duration and heat release rate are also investigated.

Three fuels with cetane numbers of 45, 36 and 29 have been run at four load levels at each of three speeds in a Detroit: Diesel 3–71 engine with standard injectors. Measurements of temperatures, pressures, Load, fuel flow, cylinder pressure in one cylinder, strain gauge measurements from the rocker arm operating one injector and exhaust emissions were all recorded. Comparisons show little change in operation except for increases in ignition delay and rate of cylinder pressure rise with the low cetane fuels. It was concluded, on the basis of these short runs, that the intermediate fuel probably would not cause major difficulties but the lowest cetane fuel could possibly present problems with noise and engine durability.

Six experimental fuels representative of Canadian future fuel options were tested against a reference fuel in a Bombardier 12 cylinder, 4 stroke, 3000 hp, medium speed diesel. The reference fuel was a straight run ASTM #2-D. The first test fuel blend consisted of heavy atmospheric gas oil that extended the distillation range (higher end point) of the other blend component ASTM #2-D. The second fuel was a blend of a distillate cut from a mixture of conventional and tar sands crude with hydrogen treated cracked stock. This provided a fuel with substantial levels of aromatic and cracked components. The third fuel was gas oil side stream: a low cetane number, high aromatics level tar sands distillate. The fourth fuel was an equal portion blend of tar sands crude components, gas oil side-stream and heavy unifined gas oil. The fifth fuel was a blend of ASTM #2-D heating oil and a substantial portion of stabilized cracked stock.

Two Canadian tar sands derived experimental diesel fuels with cetane numbers of 26 and 36 and a reference fuel with a cetane number of 47 were tested in a Deutz (F1L511D), single cylinder, A stroke, naturally aspirated research engine. The fuels were tested at intake and cooling air temperatures of 30 and 0°C. The 36 cetane number fuel was tested with advanced, rated and retarded injection timings. Poor engine speed stability at light loads and excessive rates of combustion pressure rise were experienced with the lowest cetane number fuel. Detailed performance/combustion behavior is presented and a correlation with fuel structural composition is made. The analytical techniques used to characterize the fuels included liquid chromatography, gas chromatography mass spectrometry (GC-MS) and proton nuclear magnetic resonance spectrometry (PNMR).

Controlled Auto-Ignition (CAI), also known as Homogeneous Charge Compression Ignition (HCCI), has the potential to improve gasoline engines’ efficiency and simultaneously achieve ultra-low NOx emissions. Two of the primary obstacles for applying CAI combustion are the control of combustion phasing and the maximum heat release rate. To solve these problems, dimethyl ether (DME) was directly injected into the cylinder to generate multi-point micro-flame through compression in order to manage the entire heat release of gasoline in the cylinder through port fuel injection, which is known as micro-flame ignited (MFI) hybrid combustion.

Pumping Mean Effective Pressure (PMEP) is the main factor limiting the improvement of thermal efficiency in a spark-ignition (SI) engine under low load. One of the ways to reduce the pumping loss under low load is to use Cylinder DeActivation (CDA). The CDA aims at reducing the firing density (FD) of the SI engine under low load operation and increasing the mass of air-fuel mixture within one cycle in one cylinder to reduce the throttling effect and further reducing the PMEP. The multi-stroke cycles can also reduce the firing density of the SI engine after some certain reasonable design, which is feasible to improve the thermal efficiency of the engine under low load in theory. The research was carried out on a calibrated four-cylinder SI engine simulation platform. The thermal efficiency improvements of the 6-stroke cycle and 8-stroke cycle to the engine performance were studied compared with the traditional 4-stroke cycle under low load conditions.