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Journal Article

A Comparative Study of a Spark Ignition Engine Running on Hydrogen, Synthesis Gas and Natural Gas

This paper presents an experimental, numerical and theoretical study of the performance of the same spark ignition engine running on four different gaseous fuels: hydrogen, two synthesis gases and natural gas. Measurements of the brake thermal efficiency, the combustion variability, the engine out emissions and the indicated, pumping and friction mean effective pressures are first presented, with particular interest placed on the lean burn performance. Combustion analysis is then undertaken, with the crank angle resolved in-cylinder turbulence and the flame propagation plotted on the so-called ‘Bradley diagram’ for turbulent premixed combustion. The loci of the combustion events on the Bradley diagram are then used to explain the observed, relative performance of the engine running on these four fuels.
Technical Paper

A Comparison of Four Methods for Determining the Octane Index and K on a Modern Engine with Upstream, Port or Direct Injection

Combustion in modern spark-ignition (SI) engines is increasingly knock-limited with the wide adoption of downsizing and turbocharging technologies. Fuel autoignition conditions are different in these engines compared to the standard Research Octane Number (RON) and Motor Octane Numbers (MON) tests. The Octane Index, OI = RON - K(RON-MON), has been proposed as a means to characterize the actual fuel anti-knock performance in modern engines. The K-factor, by definition equal to 0 and 1 for the RON and MON tests respectively, is intended to characterize the deviation of modern engine operation from these standard octane tests. Accurate knowledge of K is of central importance to the OI model; however, a single method for determining K has not been well accepted in the literature.
Journal Article

An Integrated Model of Energy Transport in a Reciprocating, Lean Burn, Spark Ignition Engine

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.
Technical Paper

An Optical and Numerical Characterization of Directly Injected Compressed Natural Gas Jet Development at Engine-Relevant Conditions

Compressed natural gas (CNG) is an attractive, alternative fuel for spark-ignited (SI), internal combustion (IC) engines due to its high octane rating, and low energy-specific CO2 emissions compared with gasoline. Directly-injected (DI) CNG in SI engines has the potential to dramatically decrease vehicles’ carbon emissions; however, optimization of DI CNG fueling systems requires a thorough understanding of the behavior of CNG jets in an engine environment. This paper therefore presents an experimental and modeling study of DI gaseous jets, using methane as a surrogate for CNG. Experiments are conducted in a non-reacting, constant volume chamber (CVC) using prototype injector hardware at conditions relevant to modern DI engines. The schlieren imaging technique is employed to investigate how the extent of methane jets is impacted by changing thermodynamic conditions in the fuel rail and chamber.
Technical Paper

Comparison of Pfi and Di Superbike Engines

Gasoline Direct Injection (DI) is a technique that was successful in motor sports several decades ago and is now relatively popular in passenger car applications only. DI gasoline fuel injectors have been recently improved considerably, with much higher fuel flow rates and much finer atomization enabled by the advances in fuel pressure and needle actuation. These improved injector performance and the general interest in reducing fuel consumption also in motor sports have made this option interesting again. This paper compares Port Fuel Injection (PFI) and DI of gasoline fuel in a high performance, four cylinder spark ignition engine for super bike racing. Computations are performed with a code for gas exchange, heat transfer and combustion, simulating turbulent combustion and knock.
Journal Article

Development of a Direct Injection High Efficiency Liquid Phase LPG Spark Ignition Engine

Direct Injection (DI) is believed to be one of the key strategies for maximizing the thermal efficiency of Spark Ignition (SI) engines and meet the ever-tightening emissions regulations. This paper explores the use of Liquefied Petroleum Gas (LPG) liquid phase fuel in a 1.5 liter SI four cylinder gasoline engine with double over head camshafts, four valves per cylinder, and centrally located DI injector. The DI injector is a high pressure, fast actuating injector enabling precise multiple injections of the finely atomized fuel sprays. With DI technology, the injection timing can be set to avoid fuel bypassing the engine during valve overlap into the exhaust system prior to combustion. The fuel vaporization associated with DI reduces combustion chamber and charge temperatures, thereby reducing the tendency for knocking. Fuel atomization quality supports an efficient combustion process.
Technical Paper

Exploring the Charge Composition of SI Engine Lean Limits

In this paper the experimental performance of the lean limits is examined for two different types of engines the first a dedicated LPG high compression ratio 2-valve per cylinder engine (Ford of Australia MY 2001 AU Falcon) and the second a gasoline moderate compression 4-valve per cylinder variant of the same engine (Ford of Australia MY 2006 BF Falcon). The in-cylinder composition at the lean limit over a range of steady state operating conditions is estimated using a quasi-dimensional model. This makes it possible to take into account the effects of both residual fraction and fresh charge diluents (EGR and excess air) that allow the exploration of a modeled lean limit performance [1, 2]. The results are compared to the predictions from a model for combustion variability applied to the quasi-dimensional model operating in optimization mode.
Technical Paper

HAJI Operation in a Hydrogen-Only Mode for Emission Control at Cold Start

The HAJI (Hydrogen Assisted Jet Ignition) system for S.I. engines utilises direct injection of small amounts of hydrogen to enhance the combustion of a variety of automotive fuels. Although not the primary purpose of HAJI, the hardware, once in place, also lends itself to the possibility of hydrogen-only running during a cold start. Cold-start simulations have been performed using a single cylinder engine. Results are presented, comparing hydrogen-only tests with standard HAJI operation and normal spark-ignition operation. HAJI and spark ignition tests were carried out with gasoline as the main-chamber fuel. Emission levels and combustion stability characteristics were recorded as the engine warmed up. The differences between the various fueling/ignition scenarios are presented and the implications for possible automotive applications are discussed in light of current and proposed emissions legislation.
Technical Paper

Hydrocarbon Emissions from a HAJI Equipped Ultra-lean Burn SI Engine

Hydrogen Assisted Jet Ignition (HAJI) is a novel method of maintaining combustion stability during ultra-lean operation of conventional, homogeneously charged, SI engines. When operating with HAJI above λ=2, CO and NOx emissions fall to low levels while HC emissions rise to approximately double their stoichiometric value. HC emissions were investigated by operating a HAJI equipped, optically accessible, four-valve single cylinder engine at 600 r/min, wide open throttle (WOT), and from λ=1 to λ=2.4. A fast flame ionisation detector was used to collect real time hydrocarbon concentration data from behind one of the exhaust valves, inside the HAJI pre-chamber, and from near the combustion chamber wall. Flame images were also obtained. Exhaust port sampling shows that the HC concentration during blowdown and early exhaust is increased, but the concentration at the end of exhaust is decreased.
Technical Paper

Hydrogen as a Fuel in SI Engines - Towards Best Efficiency for Car Applications

The goal of hydrogen engine research is to achieve highest possible efficiency with low NOx emissions. This is necessary for the hydrogen car to remain competitive with the ever-improving efficiency of conventional fuel's use, to take advantage of the increased availability of hydrogen distribution for fuel cells and to achieve better range than battery electric vehicles. This paper examines the special problems of hydrogen engine combustion and ways to improve efficiency. Central to this are the effects of compression ratio (CR) and lambda (excess air ratio) and ignition system. The results demonstrate highest indicated thermal efficiency at ultra lean condition of lambda ≻ 2 and with central ignition. This need for this lean mixture is partly explained by the higher heat transfer losses.
Technical Paper

Lean Burn Performance of a Natural Gas Fuelled, Port Injected, Spark Ignition Engine

This paper presents a study of the performance of a lean burn, natural gas-fuelled, naturally aspirated, spark ignition engine for an E class vehicle. Engine performance and exhaust emissions (NO, CO, and UHC) data are first discussed. An energy balance of the engine operating at different loads and air-fuel ratios is then presented, and used to explain why engine efficiency varies with air-fuel ratio. Finally, the hot start drive cycle CO2e (CO2 equivalent) emissions are estimated for a vehicle with this engine. This shows a potential for significant reduction in vehicle greenhouse gas emissions compared to an equivalent gasoline-fuelled vehicle.
Technical Paper

Modeling of Trace Knock in a Modern SI Engine Fuelled by Ethanol/Gasoline Blends

This paper presents a numerical study of trace knocking combustion of ethanol/gasoline blends in a modern, single cylinder SI engine. Results are compared to experimental data from a prior, published work [1]. The engine is modeled using GT-Power and a two-zone combustion model containing detailed kinetic models. The two zone model uses a gasoline surrogate model [2] combined with a sub-model for nitric oxide (NO) [3] to simulate end-gas autoignition. Upstream, pre-vaporized fuel injection (UFI) and direct injection (DI) are modeled and compared to characterize ethanol's low autoignition reactivity and high charge cooling effects. Three ethanol/gasoline blends are studied: E0, E20, and E50. The modeled and experimental results demonstrate some systematic differences in the spark timing for trace knock across all three fuels, but the relative trends with engine load and ethanol content are consistent. Possible reasons causing the differences are discussed.
Technical Paper

Modeling the Effects of Mixture Composition on Cyclic Variability

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.
Technical Paper

Observation of the Effect of Swirl on Flame Propagation and the Derived Heat Release and Mass Burning Rates

A high speed research engine has optical access to over 80% of the combustion chamber volume through a piston with a quartz window. The engine has been used to study the effect of swirl on the spark-ignited combustion by means of high speed photography and analysis of combustion-time data. Results over the speed, swirl and mixture strength range show the flame travel derived from the pressure to agree with the measured flame travel to within 3% on average. Turbulent to laminar flame speed ratios as high as 45 occur under high swirl conditions. However it was not possible to find a predictive model which could explain the turbulent flame speed in terms of engine design variables.
Technical Paper

Optimization of All SI Engine Combustion Control and Related Events for Efficiency

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.
Technical Paper

Optimized Design of a Cyclic Variability Constrained Lean Limit SI Engine at Optimum NOx and Efficiency Using a PSO Algorithm

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.
Technical Paper

Performance of a Port Fuel Injected, Spark Ignition Engine Optimised for Hydrogen Fuel

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.
Technical Paper

Simulation of Spark Ignition Engine Combustion Using Lagrangian Code

A new method of solution is presented for the equations governing unsteady flow field during compression and combustion in a spark ignition. The Lagrangian approach, an application of a vortex method to the three-dimensional solution of the continuity and conservation equations, avoids the need for a turbulence model and wall laws close to the surfaces. Vorticity is introduced as blobs close to the wall which diffuse into the main flow. The potential equation is solved by the boundary element method. Combustion is treated as a thin sheet propagating at laminar flame speed using an extension of the simple line interface method to three-dimensions, now called a simple plane interface method. The code is demonstrated in application to a wedge shaped combustion chamber with surface irregularities closely approximating the actual shape.
Technical Paper

Spatial and Temporal Temperature Distributions in a Spark Ignition Engine Piston at WOT

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.
Technical Paper

The Always Lean Burn Spark Ignition (ALSI) Engine – Its Performance and Emissions

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.