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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.

The Bishop Rotary Valve (BRV) has the opportunity for greater breathing capacity than conventional poppet valve engines. However the combustion chamber shape is different from conventional engine with no opportunity for a central spark plug. This paper reports the development of a combustion analysis and design model using KIVA-3V code to locate the ignition centers and to perform sensitivity analysis to several design variables. Central to the use of the model was the tuning of the laminar Arrhenius model constants to match the experimental pressure data over the speed range 13000-20000 rpm. Piston ring crevices lands and valve crevices is shown to be an important development area and connecting rod piston stretch has also been accommodated in the modeling. For the proposed comparison, a conventional 4 valve per cylinder poppet valve engine of nearly equal IMEP has been simulated with GT-POWER.

This paper extends previous development of the ALSI concept, by investigating the performance delivered with a turbocharged version of this engine. The research is based on extensive experimental research with lean burn, high compression ratio engines using hydrogen, LPG, CNG and gasoline fuels. It also builds on recent experience with highly boosted spark ignition gasoline and LPG engines and single cylinder engine research used extensively for model calibration. The final experimental foundation is the wide ranging evaluation of jet assisted ignition that generally allows a lean limit mixture shift of more than one unit of lambda with consequential benefits of improved thermal efficiency and close to zero NOx. The paper describes the capability of the ultra lean burn spark ignition engine with the mild boost needed provided by a Honeywell turbocharger.

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.

This paper explores through engine simulations the use of LPG and CNG gas fuels in a 1.5 liter Spark Ignition (SI) four cylinder gasoline engine with double over head camshafts, four valves per cylinder equipped with a novel mixture preparation and ignition system comprising centrally located Direct Injection (DI) injector and Jet Ignition (JI) nozzles. With DI technology, the fuel may be introduced within the cylinder after completion of the valve events. DI of fuel reduces the embedded air displacement effects of gaseous fuels and lowers the charge temperature. DI also allows lean stratified bulk combustion with enhanced rate of combustion and reduced heat transfer to the cylinder walls creating a bulk lean stratified mixture.

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).

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.

The application of a Scotch Yoke crank mechanism to a reciprocating internal combustion engine reduces the engine's size and weight and, with the sinusoidal piston motion it provides, it changes the combustion parameters and simplifies the requirements for perfect balancing of the engine. This paper makes a theoretical comparison between conventional and Scotch Yoke engines with dimensional similarity of individual components where possible such as bore and stroke, and justifiable differences appropriate to each engine design such as cylinder bore off-set, piston height, connecting rod length etc. Included are variations related to differences in piston motion (true sinusoidal versus conventional) such as exhaust emissions and balancing requirements.

This paper is based on extensive experimental research with lean burn, high compression ratio engines using LPG, CNG and gasoline fuels. It also builds on recent experience with highly boosted spark ignition gasoline and LPG engines and single cylinder engine research used for model calibration. The final experimental foundation is an evaluation of jet assisted ignition that generally allows a lean mixture shift of more than one unit in lambda with consequential benefits of improved thermal efficiency and close to zero NOx. The capability of an ultra lean burn spark ignition engine is described. The concept is operation at air-fuel ratios similar to the diesel engine but with essentially homogenous charge, although some stratification may be desirable. To achieve high thermal efficiency this engine has optimized compression ratio but with variable valve timing which enables reduction in the effective compression ratio when desirable.

Two coupled finite element analysis (FEA) programs were written to determine the transient and steady state temperature distribution in a spark ignition engine piston. The programs estimated the temperatures at each crank angle degree (CAD) through warm-up to thermal steady state. A commercial FEA code was used to combine the steady state temperature distribution with the mechanical loads to find the stress response at each CAD for one complete cycle. The first FEA program was a very fast and robust non-linear thermal code to estimate spatial and time resolved heat flux from the combustion chamber to the aluminum alloy piston crown. This model applied the energy conservation equation to the near wall gas and includes the effects of turbulence, a propagating heat source, and a quench layer allowing estimates of local, instantaneous near-wall temperature gradients and the resulting heat fluxes.

This paper presents a study of the performance of a 6-cylinder, spark-ignited, port-fuel-injected, production engine modified for hydrogen fueling. The engine modifications include turbo-charging, multiple fuel injectors per port and charge-dilution control techniques. Pumping losses are reduced through ultra-lean burn and throttle-less operation alongside high charge dilution ratio control achieved by twin independent variable cam timing without external EGR. Lean-burn combustion, engine-out emissions and brake thermal efficiency results are examined in detail. In particular, low NO emissions and brake thermal efficiencies near 38% are observed experimentally at the same operating conditions. The former is explained in terms of the usual thermal NOx pathway. Usage of throttle position, injection timings and cam timings for avoiding preignition and knock over the entire engine map are also discussed.

HAJI (Hydrogen Assisted Jet Ignition) is an advanced combustion initiation system for otherwise standard S.I engines. It utilises the fluid mechanics of a turbulent, chemically active jet, combined with the reliability of spark igniting rich hydrogen mixtures. The result is an extremely robust ignition system, capable of developing power from an engine charged with air-fuel mixtures as lean as λ = 5. Experiments have been performed using a single cylinder engine operating on gasoline in the speed range of 600-1800 r/min. Data are presented in the form of maps which describe fuel efficiency, combustion stability and emissions with respect to load, speed, air-fuel ratio and throttle. The results are incorporated into a model of a known engine and vehicle and this is used to estimate performance over the Federal drive-cycle.

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.

There are two parts to achieving the optimization reported here. The development of an engine simulation model and an optimization algorithm. The engine performance is evaluated using a quasi-dimensional engine combustion model with sub models to incorporate friction, heat losses and abnormal combustion, that is knocking. After extensive search and development a new Particle Swarm Optimizer (PSO), has been developed. Optimization includes, for the first time, the search of discontinuous design variables. The input variables considered for this investigation are manifold air pressure, air-fuel ratio, spark timing, compression ratio, valve timing events including valve open duration, maximum valve lift and engine speed. This enables the identification of the maximum thermal efficiency at a given power output at any engine operating speed.

Favorable and unfavorable properties of hydrogen as a combustion engine fuel have been accommodated in a design of a fuel efficient and clean engine providing similar to gasoline maximum torque and power. The advanced H2ICE being developed is a turbocharged engine fitted with cryogenic port hydrogen fuel injection and the hydrogen assisted jet ignition (HAJI). The combustion chamber is designed to produce a high compression ratio and therefore high thermal efficiency. A waste gated turbocharger provides pressure boosting for an increased power density running ultra lean for SULEV operation without after treatment. Thanks to the combustion properties of hydrogen further enhanced by the HAJI system, the engine load is mainly controlled throttle-less decreasing the fuel-to-air equivalence ratio from ultra lean ϕ=0.43 to ultra-ultra lean ϕ=0.18. The computational model developed for addressing the major design issues and the predicted engine performance and efficiency maps are included.

In spark ignited engine maximum thermal efficiency is found with lean mixtures. The authors' models for optimizing engine design show a preference for burning at the lean limit which to date has been found from experimental measurements. Hence ignoring combustion variability in the modeling can cause significant error in engine performance and emissions at or close to the lean limit. To aid in optimizing engine design, a model is needed that allows the inclusion of variability in the search for lean operation solutions. Here a useful addition to modeling is presented - a physically based lean limit model that can allow the lean limit to be set as non-dimensional COV of IMEP or as a variance in IMEP. The current work focuses on predicting the increase of cyclic variability due to the dilution of the mixture, whether by EGR and residual gas or by excess air.

Gas assisted jet ignition is a prechamber combustion initiation system for conventional spark ignition engines. With the system, a chemically active turbulent jet is used to initiate combustion in lean fuel mixtures enabling reliable combustion over a much broader range of air-fuel ratios. The extended range is due to the distributed ignition source provided by the jet, which can overcome the problems of poorly mixed main chamber charges and slower burning fuels. In addition, the ability to reliably ignite lean mixtures improves the thermal efficiency and enables ultra low emission levels. Experiments together with flame propagation modeling completed using STAR-CD with CHEMKIN Kinetics were done in order to examine the effects of numerous prechamber fuels on the ignition of the main fuel, which consisted of either liquefied petroleum gas (LPG) or gasoline.

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.

A high compression ratio, single cylinder, open chamber diesel engine was converted to operate on homogenously charged compressed natural gas (CNG) with the aim of minimising pollutant emissions such as oxides of nitrogen, particulate matter and carbon dioxide. Three ignition systems were tested including spark ignition (SI), diesel pilot ignition (DPI) and hydrogen assisted jet ignition (HAJI). Irrespective of ignition system used, the efficiency of the engine operating on CNG was significantly reduced at part load compared to diesel. This was predominantly due to a greater amount of unburnt hydrocarbons, higher cycle-by-cycle variability, slow and partial burns and increased heat transfer to the walls. DPI and HAJI systems were able to extend the lean limit to lambda 2.7 and 3.3 respectively, however this did not result in efficiency gains.