Search Results

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.

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.

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.

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.

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.

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 presents experimental and computational results obtained on an in line, six cylinder, naturally aspirated, gasoline engine. Steady state measurements were first collected for a wide range of cam and spark timings versus throttle position and engine speed at part and full load. Simulations were performed by using an engine thermo-fluid model. The model was validated with measured steady state air and fuel flow rates and indicated and brake mean effective pressures. The model provides satisfactory accuracy and demonstrates the ability of the approach to produce fairly accurate steady state maps of BMEP and BSFC. However, results show that three major areas still need development especially at low loads, namely combustion, heat transfer and friction modeling, impacting respectively on IMEP and FMEP computations. Satisfactory measurement of small IMEP and derivation of FMEP at low loads is also a major issue.

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).

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.

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 describes the turbocharger development of a restricted 430 cm3 odd firing two cylinder engine. The downsized test engine used for development was specifically designed and configured for Formula SAE, SAE's student Formula race-car competition. A well recognised problem in turbocharging Formula SAE engines arises from the rules, which dictate that the throttle and air intake restrictor must be on the suction side of the compressor. As a consequence of upstream throttling, oil from the compressor side seal assembly is drawn into the inlet manifold. The development process used to solve the oil consumption issue for a Garrett GT-12 turbocharger is outlined, together with cooling and control issues. The development methodology used to achieve high pressure ratio turbocharging is discussed, along with exhaust manifold development and operating limitations. This includes experimental and modeling results for both pulse and constant pressure type turbocharging.

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.

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).

This paper describes the design and development of a gasketless interface, which was used successfully to couple an aluminium cylinder head to an open deck design cylinder block. The cylinder block was manufactured from aluminium, featuring shrink fit dry cast iron liners. Extensive CAE modelling was employed to implement the gasketless interface and thus avoid using a conventional metal or fiber based cylinder head gasket. The engine was specifically designed and configured for the purpose, being a 430 cm3, highly turbocharged (TC) twin cylinder in-line arrangement with double overhead camshafts and four valves per cylinder. Most of the engine components were specially cast or machined from billets. The new design removed the conventional head gasket and relied on the correct amount of face pressure generated by interference between the cylinder head and block to seal the interface. This had advantages in improving the structural integrity of the weak open deck design.

This paper describes the design and development of an engine with constant power for SAE's student Formula race-car competition, allowing the avoidance of gear shifting for much of the Autocross event. To achieve constant power for over 50% of the speed range, turbocharging was adopted with a boost pressure ratio of 2.8 at mid-range speeds and applied to an engine capacity of 430 cc. This engine was specifically designed and configured for the purpose, being a twin cylinder in-line arrangement with double overhead camshafts. Most of the engine components were specially cast or machined from billets. The capacity was selected to minimise frictional losses and thus increase delivered power along with dry sump lubrication and a three speed gear box. The engine manifolds and plenums were designed using a CAE application and proved to be well suited to the task resulting in excellent agreement between predicted and actual performance.

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.

Diesel engines are used in heavy duty applications because of their high efficiency and reliability. However, their high diesel particulates and NOx emissions remain major concerns. An eight cylinder direct injection diesel engine was connected to a partial flow particulate sampling mini-dilution tunnel. Six different grades of diesel fuels were studied for their regular emissions as well as smoke and particulate emissions. Each fuel was tested at three engine speeds and full load. This paper presents the results of these tests which includes analysis of the effects of load, cetane number, 90% distillation temperature, and density for steady state conditions. A correlation was developed for converting smoke numbers in Hartridge Smoke Units (HSU) to the specific particulate emissions by evaluating results of all fuels tests. Another correlation was also developed for diesel particulates and NOx emissions trade-off.

An adaptive air fuel ratio (AFR) control system has been implemented on a modern high performance fuel injected four cylinder engine. A pressure transducer in the combustion chamber is used to measure the indicated mean effective pressure (IMEP) for efficiency and cyclic variability feedback. The controller tunes the relative AFR, λ, in the range λ = 1 to λ = 1.5, to maximise the thermal efficiency in real time. The system adaptively accounts for changes in operating conditions such as ambient temperatures and user demands. The IMEP feedback allows the closed loop control system to update every few revolutions with short tune in times in the order of seconds. Open and closed loop test results are presented, demonstrating the incremental efficiency gains over fixed or mapped AFR control. The system continually adjusts the fuelling for maximum efficiency given its constraints and provides a basis for optimisation of future lean burn technologies.

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.