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Many applications of liquefied petroleum gas (LPG) to commercial vehicles have used their corresponding diesel engine counterparts for their basic architecture. Here a review is made of the application to commercial vehicle operation of a robust 4 L, light-duty, 6-cylinder in-line engine produced by Ford Australia on a unique long-term production line. Since 2000 it has had a dedicated LPG pick-up truck and cab-chassis variant. A sequence of research programs has focused on optimizing this engine for low carbon dioxide (CO₂) emissions. Best results (from steady state engine maps) suggest reductions in CO₂ emissions of over 30% are possible in New European Drive Cycle (NEDC) light-duty tests compared with the base gasoline engine counterpart. This has been achieved through increasing compression ratio to 12, running lean burn (to λ = 1.6) and careful study (through CFD and bench tests) of the injected LPG-air mixing system.

Turbulent Jet Ignition is an advanced pre-chamber initiated combustion system for an otherwise standard spark ignition engine found in current on-road vehicles. This next-generation pre-chamber design overcomes previous packaging obstacles by simply replacing the spark plug in a modern four-valve, pent roof spark ignition engine. Turbulent Jet Ignition enables very fast burn rates due to the ignition system producing multiple, distributed ignition sites, which consume the main charge rapidly and with minimal combustion variability. The fast burn rates allow for increased levels of dilution (lean burn and/or EGR) when compared to conventional spark ignition combustion, with dilution levels being comparable to other low temperature combustion technologies (homogeneous charge compression ignition - HCCI) without the complex control drawbacks.

This paper provides some insight into the future direction for developing smaller capacity downsized engines, which will be needed to meet tight CO₂ targets and the world's future powertrain requirements. This paper focuses on the combustion system development and combustion analysis results for a downsized 0.43-liter highly turbocharged engine. The inline two-cylinder engine used in experiments was specifically designed and constructed to enable 25 bar BMEP. Producing this specific output is one way forward for future passenger vehicle powertrains, enabling in excess of 50% swept capacity reduction whilst maintaining comparable vehicle performance. Previous experiments and analysis have found that the extent to which larger engines can be downsized while still maintaining equal performance is combustion limited.

Turbulent jet ignition is a pre-chamber ignition enhancement method that produces a distributed ignition source through the use of a chemically active turbulent jet which can replace the spark plug in a conventional spark ignition engine. In this paper combustion visualization and characterization was performed for the combustion of a premixed propane/air mixture initiated by a pre-chamber turbulent jet ignition system with no auxiliary fuel injection, in a rapid compression machine. Three different single orifice nozzles with orifice diameters of 1.5 mm, 2 mm, and 3 mm were tested for the turbulent jet igniter pre-chamber over a range of air to fuel ratios. The performance of the turbulent jet ignition system based on nozzle orifice diameter was characterized by considering both the 0-10 % and the 10-90 % burn durations of the pressure rise due to combustion.

Autoignition delay times of two full blend gasoline fuels (high and low RON) were explored in a rapid compression machine. CO2 dilution by mass was introduced at 0%, 15%, and 30% levels with the O2:N2 mole ratio fixed at 1:3.76. This dilution strategy is used to represent exhaust gas recirculation (EGR) substitution in spark ignition (SI) engines by using CO2 as a surrogate for major EGR constituents(N2, CO2, H2O). Experiments were conducted over the temperature range of 650K-900K and at 10 bar and 20 bar compressed pressure conditions for equivalence ratios of (Φ =) 0.6-1.3. The full blend fuels were admitted directly into the combustion chamber for mixture preparation using the direct test chamber (DTC) approach. CO2 addition retarded the autoignition times for the fuels studied here. The retarding effect of the CO2 dilution was more pronounced in the NTC region when compared to the lower and higher temperature range.

This paper presents a combined experimental and numerical method for analysing energy flows within a spark ignition engine. Engine dynamometer data is combined with physical models of in-cylinder convection and the engine's thermal impedances, allowing closure of the First Law of Thermodynamics over the entire engine system. In contrast to almost all previous works, the coolant and metal temperatures are not assumed constant, but rather are outputs from this approach. This method is therefore expected to be most useful for lean burn engines, whose temperatures should depart most from normal experience. As an example of this method, the effects of normalised air-fuel ratio (λ), compression ratio and combustion chamber geometry are examined using a hydrogen-fueled engine operating from λ = 1.5 to λ = 6. This shows large variations in the in-cylinder wall temperatures and heat transfer with respect to λ.

Lean combustion is a promising combustion technology that has the potential to improve engine efficiency while decreasing emissions. One reason why lean combustion has not been more widely implemented is that as the air-fuel ratio increases, the resulting flame propagation speed becomes slower and combustion becomes unstable. Turbulent jet ignition is a pre-chamber ignition enhancement concept that facilitates ultra-lean combustion by using a hot combusting jet as a distributed ignition source. The jet penetration allows for shorter flame travel distances, which decreases the overall burn duration and improves stability. By using a rich mixture in the pre-chamber, the pre-chamber mixture is easily ignitable and the transport of chemically active radical species and unburned fuel into the main-chamber charge improves ignition quality.

Previous studies have shown that several facility dependent factors can influence ignition delay times measured in a rapid compression machine. Compression ratio variation represents one such aspect of many facility-to facility differences in RCMs, and can have a major impact on measured ignition delay times due to changes in surface-area-to-volume ratio, initial conditions and compression duration even when the same compressed conditions are maintained. In this study, iso-octane, which exhibits two stage ignition delay and has a pronounced negative temperature coefficient (NTC) region, is used to investigate the effects of changing compression ratio on ignition delay. Resulting trends are also compared to previous results obtained with ethanol, which has very different combustion properties. Experiments were carried out for rich mixtures (ϕ = 1.3) of iso-octane and air over a compressed temperature range of 675-900 K at 20 bar compressed pressure.

This paper presents a comparison of the influence of different mixture preparation strategies on gaseous fuel combustion in SI engines. Three mixture preparation strategies are presented for a dedicated LPG fuelled engine, showing varying results - gaseous phase port injection (PFI-G), liquid-phase port injection (PFI-L) and gaseous-phase throttle-body injection (TBI-G). Previous work by the authors has shown considerable differences in emissions and thermal efficiency between different fuelling strategies. This paper extends this work to the area of combustion characteristics and lean limit operation and closer analyses the differences between these systems. A dedicated LPG in-line six cylinder engine with compression ratio increased to 11.7:1 (up from the standard 9.65:1) was tested over a range of speed/torque conditions representing most of the steady-state parts of the Euro drive-cycle for light duty-vehicles. The air-fuel ratio was varied from lambda 1.0 to the lean limit.

This study focuses on the combustion visualization of spark ignition combustion in an optical single cylinder engine using natural gas and propane at several air to fuel ratios and speed-load operating points. Propane and natural gas fuels were compared as they are the most promising gaseous alternative fuels for reciprocating powertrains, with both fuels beginning to find wide market penetration on the fleet level across many regions of the world. Additionally, when compared to gasoline, these gaseous fuels are affordable, have high knock resistance and relatively low carbon content and they do not suffer from the complex re-fueling and storage problems associated with hydrogen.

This paper describes the mechanical component design, lubrication, tuning and control aspects of a restricted, odd fire, highly turbocharged (TC) engine for Formula SAE competition. The engine was specifically designed and configured for the purpose, being a twin cylinder inline arrangement with double overhead camshafts and four valves per cylinder. Most of the engine components were specially cast or machined from billets. A detailed theoretical analysis was completed to determine engine specifications and operating conditions. Results from the analysis indicated a new engine design was necessary to sustain highly TC operation. Dry sump lubrication was implemented after initial oil surge problems were found with the wet sump system during vehicle testing. The design and development of the system is outlined, together with brake performance effects for the varying systems.

Hydrogen assisted jet ignition (HAJI) is a pre-chamber ignition system for otherwise standard gasoline fueled spark ignition engines that involves the use of a chemically active turbulent jet to initiate combustion in lean fuel mixtures. HAJI burns the lean main charge rapidly and with almost no combustion variability, which allows for low hydrocarbon emissions and almost zero NOx, due to lower peak temperatures. This paper focuses on the effects of different pre-chamber fuels on combustion stability, lean limit and emissions in a single cylinder, HAJI equipped, CFR engine under a worst case, light load condition. Results indicate that the choice of pre-chamber fuel affects the main chamber lean limit but that emissions are not largely affected before this lean limit is reached. The lean limit was extended furthest, to λ = 2.5 with hydrogen, followed by λ = 2.35 with LPG, λ = 2.25 with CNG and λ = 2.15 with carbon monoxide.

In this paper, performance, efficiency and emission experimental results are presented from a prototype 434 cm3, highly turbocharged (TC), two cylinder engine with brake power limited to approximately 60 kW. These results are compared to current small engines found in today's automobile marketplace. A normally aspirated (NA) 1.25 liter, four cylinder, modern production engine with similar brake power output is used for comparison. Results illustrate the potential for downsized engines to significantly reduce fuel consumption while still maintaining engine performance. This has advantages in reducing vehicle running costs together with meeting tighter carbon dioxide (CO2) emission standards. Experimental results highlight the performance potential of smaller engines with intake boosting. This is demonstrated with the test engine achieving 25 bar brake mean effective pressure (BMEP).

Several race car competitions seek to limit engine power through a rule that requires all of the engine combustion air passes through a hole of prescribed diameter. As the approach and departure wall shapes to this hole, usually termed orifice or restrictor are not prescribed, there is opportunity for innovation in these shapes to obtain maximum flow and therefore power. This paper reports measurements made for a range of restrictor types including venturis with conical inlets and outlets of various angles and the application of slotted throats of the ‘Dall tube’ type. Although normal venturis have been optimized as subsonic flow measuring devices with minimum pressure losses, at the limit the flow in the throat is sonic and the down stream shocks associated with flow transition from sub-sonic to sonic are best handled with sudden angular changes and the boundary layer minimized by the corner slots between the convergent and divergent cones.

In recent times new tools have emerged to aid the optimization of engine design. The particle swarm optimizer, used here is one of these tools. However, applying it to the optimization of the S.I. engine for high efficiency and low NOx emission has shown the preference of ultra lean burn strategy combined with high compression ratios. For combined power, efficiency and emissions benefits, there are two restricting factors, limiting the applicability of this strategy, knocking and cyclic variability. In the ultra lean region, knocking is not an important issue but the variability is a major concern. This paper demonstrates the application of a variability model to limit the search domain for the optimization program. The results show that variability constrains the possible gains in fuel consumption and emission reduction, through optimizing cam phasing, mixture and spark timing. The fuel consumption gain is reduced by about 11% relative.

This paper reports comparative results for liquid phase versus gaseous phase port injection in a single cylinder engine. It follows previous research in a multi-cylinder engine where liquid phase was found to have advantages over gas phase at most operating conditions. Significant variations in cylinder to cylinder mixture distribution were found for both phases and leading to uncertainty in the findings. The uncertainty was avoided in this paper as in the engine used, a high speed Waukesha ASTM CFR, identical manifold conditions could be assured and MBT spark found for each fuel supply system over a wide range of mixtures. These were extended to lean burn conditions where gaseous fuelling in the multi-cylinder engine had been reported to be at least an equal performer to liquid phase. The experimental data confirm the power and efficiency advantages of liquid phase injection over gas phase injection and carburetion in multi-cylinder engine tests.

This paper compares the performance, efficiency, emissions and combustion parameters of a prototype two cylinder 430 cm3 engine which has been tested in a variety of normally aspirated (NA) modes with compression ratio (CR) variations. Experiments were completed using 98-RON pump gasoline with modes defined by alterations to the induction system, which included carburetion and port fuel injection (PFI). The results from this paper provide some insight into the CR effects for small NA spark ignition (SI) engines. This information provides future direction for the development of smaller engines as engine downsizing grows in popularity due to rising oil prices and recent carbon dioxide (CO2) emission regulations. Results are displayed in the engine speed, manifold absolute pressure (MAP) and CR domains, with engine speeds exceeding 10000 rev/min and CRs ranging from 9 to 13. Combustion analysis is also included, allowing mass fraction burn (MFB) comparison.

Hydrogen assisted jet ignition (HAJI) is a pre-chamber ignition system for standard gasoline fueled engines that involves the use of a chemically active turbulent jet to initiate combustion in lean fuel mixtures. HAJI burns the lean main charge rapidly and with almost no combustion variability, which allows for low hydrocarbon emissions and almost zero NOx, due to lower peak temperatures. This paper focuses on the effects of internal and cooled external exhaust gas recirculation (EGR) on combustion parameters, emissions and thermal efficiency in a single cylinder HAJI equipped CFR engine. Experimental results indicate that replacing air with EGR in λ=2 mixtures can shift the lean limit at which NOx is negligible to mixtures as rich as λ=1.3, without a large penalty in hydrocarbon emissions and thermal efficiency.

New concepts in oxygen enrichment of the inlet air have been examined in tests on two direct injection diesel engines, showing: significant reduction in particulate emissions (nearly 80% at full load), increased thermal efficiency if injection timing control is employed, substantial reductions in exhaust smoke under most conditions, ability to burn inferior quality fuels which is economically very attractive and achivement of turbo-charged levels of output with consequential benefits of increased power/mass and improved thermal efficiency. The replacement of an engine's turbocharger and intercooling system with a smaller turbocharger and polymeric membrane elements to supply the oxygen enriched stream should allow improved transient response. NOx emission remain a problem and can only be reduced to normally aspirated engine levels at some efficiency penalty.

This paper compares the performance of a small two cylinder, 430 cm3 engine which has been tested in a variety of normally aspirated (NA) and forced induction modes on 98-RON pump gasoline. These modes are defined by variations in the induction system and associated compression ratio (CR) alterations needed to avoid knock and maximize volumetric efficiency (ηVOL). These modes included: (A) NA with carburetion (B) NA with port fuel injection (PFI) (C) Mildly Supercharged (SC) with PFI (D) Highly Turbocharged (TC) with PFI The results have significant relevance in defining the limitations for small downsized spark ignition (SI) engines, with power increases needed via intake boosting to compensate for the reduced swept volume. Performance is compared in the varying modes with comparisons of brake mean effective pressure (BMEP), brake power, ηVOL, brake specific fuel consumption (BSFC) and brake thermal efficiency (ηTH).