Search Results

A prior study (Chon and Heywood, [1]) examined how the design and performance of spark-ignition engines evolved in the United States during the 1980s and 1990s. This paper carries out a similar analysis of trends in basic engine design and performance characteristics over the past decade. Available databases on engine specifications in the U.S., Europe, and Japan were used as the sources of information. Parameters analyzed were maximum torque, power, and speed; number of cylinders and engine configuration, cylinder displacement, bore, stroke, compression ratio; valvetrain configuration, number of valves and their control; port or direct fuel injection; naturally-aspirated or turbocharged engine concepts; spark-ignition and diesel engines. Design features are correlated with these engine’s performance parameters, normalized by engine and cylinder displacement.

Since the advent of the spark ignition engine, the maximum engine efficiency has been knock limited. Knock is a phenomena caused by the rapid autoignition of fuel/air mixture (endgas) ahead of the flame front. The propensity of a fuel to autoignite corresponds to its autoignition chemistry at the local endgas temperature and pressure. Since a fuel blend consists of many components, its autoignition chemistry is very complex. The octane index (OI) simplifies this complex autoignition chemistry by comparing a fuel to a Primary Reference Fuel (PRF), a binary blend of iso-octane and n-heptane. As more iso-octane is added into the blend, the PRF is less likely to autoignite. The OI of a fuel is defined as the volumetric percentage of iso-octane in the PRF blend that exhibits similar knocking characteristics at the same engine conditions.

This paper discusses the influences of several cylinder liner honing surface geometrical features on the interaction between the piston twin land oil control ring (TLOCR) and the cylinder liner by using the deterministic hydrodynamic model [1] and the twin land oil control ring model [2]. Additionally, the key design parameters of the TLOCR, including ring tension and land axial width are studied. The results show significant effects of three liner honing surface features beyond height distribution, including plateau wavelength, groove density and honing angle in hydrodynamic pressure generation. The study in oil control ring design parameters reveals that both ring tension and land axial width have important influences on friction and oil consumption, and their competing effects are discussed subsequently.

The way In which combustion chamber geometry affects combustion in SI engines was studied using a quasi-diraensional cycle simulation. Calculations were performed to investigate the following questions: (i) the sensitivity of geometric effects on combustion to engine operating conditions; (ii) the differences in burn duration between ten chamber geometries and spark plug locations; and (iii) the relative merits of improved chamber design and amplified turbulence as means to reduce burn duration. The results from these studies are presented and discussed.

As a part of the effort to comply with increasingly stringent emission standards, engine manufacturers strive to minimize engine oil consumption. This requires the advancement of the understanding of the characteristics, sources, and driving mechanisms of oil consumption. This paper presents a combined theoretical and experimental approach to separate and quantify different oil consumption sources in a production spark ignition engine at different speed and load conditions. A sulfur tracer method was used to measure the dependence of oil consumption on engine operating speed and load. Liquid oil distribution on the piston was studied using a Laser-Induced-Fluorescence (LIF) technique. In addition, important in-cylinder parameters for oil transport and oil consumption, such as liner temperatures and land pressures, were measured.

Engine Hydrocarbon (HC) emissions behaviors in the shut down and re-start processes were examined in a production 4-cylinder 2.4 L engine. Depending on when the power to the ECU was cut off relative to the engine events, there could be two or three mis-fired cylinders (i.e. cylinders with fuel injected but no ignition). The total HC pumped out by the engine into the catalyst in the stopping process was ∼ 4 mg (approximately equaled to the amount of one injection at idle condition). Because the size of the catalyst was larger than the total exhaust volume in the stopping process, this HC was not observed at the catalyst exit. The catalyst temperature was also not affected. When the engine was purged after shut down (by cranking the engine with the injectors and ignition disconnected), the total exit HC was 33 mg. In a restart 90 minutes after shut down, the integrated amount of HC emissions due to residual fuel from the stopping process was 16 mg.

This study examines the scaling between engine performance, engine configuration, and engine size and geometry, for modern spark-ignition engines. It focuses especially on design features that impact engine breathing. We also analyze historical trends to illustrate how changes in technology have improved engine performance. Different geometric parameters such as cylinder displacement, piston area, number of cylinders, number of valves per cylinder, bore to stroke ratio, and compression ratio, in appropriate combinations, are correlated to engine performance parameters, namely maximum torque, power and brake mean effective pressure, to determine the relationships or scaling laws that best fit the data. Engine specifications from 1999 model year vehicles sold in the United States were compiled into a database and separated into two-, three-, and four-valves-per-cylinder engine categories.

This paper presents a study of lubricating oil transport and exchange in a four-stroke spark ignition engine while undergoing transient load changes. The study consisted of experiments with a single cylinder test engine utilizing 2D LIF (Two Dimensional Laser Induced Fluorescence) techniques to view real time oil transport and exchange, along with computer modeling to describe certain phenomenon observed during the experiments. The computer modeling results included ring dynamics and corresponding gas flows through different regions of the power cylinder. Under steady-state conditions and constant speed during the experiments, more oil was observed on the piston at low load than at high load. Therefore, a transition from low load to high load resulted in oil leaving the piston, and a transition from high load to low load resulted in oil being added to the piston.

The lubrication of the piston ring-pack is directly related to the engine friction and oil consumption. Non-axisymmetric characteristics of the power cylinder system, most noticeably cylinder bore distortion, piston secondary motion, and ring gaps, can introduce circumferential variations to ring/liner lubrication and overall performance of the ring-pack in friction and oil consumption. In order to be able to optimize the piston ring-pack in a more fundamental way, it is necessary to develop physical understanding of the effects of these non-axisymmetric properties and effective numerical tools. In this study, a comprehensive model has been developed for the lubrication of a piston ring-pack. By employing a finite element analysis, this model is capable of evaluating the in-plane structural response of a ring to external forces. A newly developed one-dimensional hydrodynamic lubrication sub-model is implemented to calculate the lubrication force at each cross-section.

A model was developed to study engine oil vaporization and oil vapor transport in the piston ring pack of internal combustion engines. With the assumption that the multi-grade oil can be modeled as a compound of a number of distinct paraffin hydrocarbons, a set of equations governing the oil vapor density variations were derived by applying mass conservation law to the amount of oil vaporized from the piston and the amount of oil vapor transported within the piston ring pack. The model was applied to a heavy-duty diesel engine. First, the case with the maximum oil supply to all the piston regions was studied. The results showed that, under this condition, the oil consumption from piston vaporization alone was far greater than the typical oil consumption value measured in the engine.

The mixture preparation and hydrocarbon (HC) emissions behaviors for a single-cylinder port-fuel-injection SI engine were examined in an engine/dynamometer set up that simulated the first cycle of cranking. The engine was motored continuously at a fixed low speed with the ignition on, and fuel was injected every 8 cycles. Unlike the real engine cranking process, the set up provided a well controlled and repeatable environment to study the cranking process. The parameters were the Engine Coolant Temperature (ECT), speed, and the fuel injection pulse width. The in-cylinder and exhaust HC were measured simultaneously with two Fast-response Flame Ionization Detectors. A large amount of injected fuel (an order of magnitude larger than the normal amount that would produce a stoichiometric mixture in a warm-up engine) was required to form a combustible mixture at low temperatures.

Gasoline HCCI engine has the potential of providing better fuel economy and emissions characteristics than the current SI engines. However, management of HCCI operation for a vehicle is a challenging task. In this paper, the issues of mode transitions between the Spark Ignition and HCCI regimes, and the dynamic nature of the load trajectory within the HCCI regime are considered. Then the phenomena encountered in these operations are illustrated by the data from a single-cylinder engine with electromagnetic-variable-valve timing control. Mode transitions from the SI to HCCI regime may be categorized as robust and non-robust. In a robust transition, every intended HCCI cycle is successful. In a non-robust transition, one or more intended HCCI cycles misfire, although the cycles progress to a satisfactory HCCI operating point in steady state. (The spark ignition was kept on so that the engine could recover from a misfired cycle.)

Homogeneous-Charge-Compression-Ignition (HCCI) engine operation in a vehicle drive cycle is a very dynamic process. In this paper, a controller is devised on the premise that the vehicle is operating under Drive-By-Wire so that the driver commands the engine torque output according to the perceived vehicle speed. Thus a load-following controller is appropriate. Such a controller was developed for a single cylinder engine with electromagnetic variable valve timing control (also known as Controlled-Auto-Ignition (CAI) operation). Under open-loop operation within the CAI regime, the results indicated that the engine response was bipolar in nature: (a) the engine either responded quasi-statically to the open-loop control, or (b) the CAI combustion failed. The latter happened in a load increase process in which the per-cycle increment was too high.

Liquid fuel flow into the cylinder an important source of hydrocarbon (HC) emissions of an SI engine. This is an especially important HC source during engine warm up. This paper examines the phenomena that determine the inflow of liquid fuel through the intake valve during a simulated start-up procedure. A Phase Doppler Particle Analyzer (PDPA) was used to measure the size and velocity of liquid fuel droplets in the vicinity of the intake valve in a firing transparent flow-visualization engine. These characteristics were measured as a function of engine running time and crank angle position during four stroke cycle. Droplet characteristics were measured at 7 angular positions in 5 planes around the circumference of the intake valve for both open and closed-valve injection. Additionally the cone shaped geometry of the entering liquid fuel spray was visualized using a Planar Laser Induced Fluorescence (PLIF) setup on the same engine.

When hydrogen is added to a gasoline fueled spark ignition engine the lean limit of the engine can be extended. Lean running engines are inherently more efficient and have the potential for significantly lower NOx emissions. In the engine concept examined here, supplemental hydrogen is generated on-board the vehicle by diverting a fraction of the gasoline to a plasmatron where a partial oxidation reaction is initiated with an electrical discharge, producing a plasmatron gas containing primarily hydrogen, carbon monoxide, and nitrogen. Two different gas mixtures were used to simulate the plasmatron output. An ideal plasmatron gas (H2, CO, and N2) was used to represent the output of the theoretically best plasmatron. A typical plasmatron gas (H2, CO, N2, and CO2) was used to represent the current output of the plasmatron. A series of hydrogen addition experiments were also performed to quantify the impact of the non-hydrogen components in the plasmatron gas.

Previous research has shown the potential benefits of running an engine with excess air. The challenges of running lean have also been identified, but not all of them have been fundamentally explained. Under high dilution levels, a lean limit is reached where combustion becomes unstable, significantly deteriorating drivability and engine efficiency, thus limiting the full potential of lean combustion. This paper expands the understanding of lean combustion by explaining the fundamentals behind this rapid rise in combustion variability and how this instability can be reduced. A flame entrainment combustion model was used to explain the fundamentals behind the observed combustion behavior in a comprehensive set of lean gasoline and hydrogen-enhanced cylinder pressure data in an SI engine. The data covered a wide range of operating conditions including different compression ratios, loads, types of dilution, fuels including levels of hydrogen enhancement, and levels of turbulence.

Experiments were performed to identify the knock trends of lean hydrocarbon-air mixtures, and such mixtures enhanced with hydrogen (H2) and carbon monoxide (CO). These enhanced mixtures simulated 15% and 30% of the engine's gasoline being reformed in a plasmatron fuel reformer [1]. Knock trends were determined by measuring the octane number (ON) of the primary reference fuel (mixture of isooctane and n-heptane) supplied to the engine that just produced audible knock. Experimental results show that leaner operation does not decrease the knock tendency of an engine under conditions where a fixed output torque is maintained; rather it slightly increases the octane requirement. The knock tendency does decrease with lean operation when the intake pressure is held constant, but engine torque is then reduced.

The effects of the directed port flow produced by a Charge-Motion-Control-Valve (CMCV) on mixture preparation in a Port-Fuel-Injection engine were assessed under conditions typical of fast idle in a cold start process. The port fuel was found to comprise two components: a “valve” puddle (at the vicinity of the valve) that built up quickly, and that was mainly responsible for the delivery of the fuel to the cylinder charge; a “port” puddle located significantly upstream. The latter was mainly created by the reverse back flow process and built up slowly. Although the fuel amounts in these two components were roughly the same, the latter did not significantly interact with the fuel transport to the cylinder charge. The CMCV only weakly affected the purging or filling time of the valve puddle, hence the dynamics of the fuel delivery process was not materially affected.

In analyzing the processes inside the cylinder of an internal combustion engine, the principal diagnostic at the experimenter's disposal is a measured time history of the cylinder pressure. This paper develops, tests, and applies a heat release analysis procedure that maintains simplicity while including the effects of heat transfer, crevice flows and fuel injection. The heat release model uses a one zone description of the cylinder contents with thermodynamic properties represented by a linear approximation for γ(T). Applications of the analysis to a single-cylinder spark-ignition engine, a special square cross-section visualization spark-ignition engine, and a direct-injection stratified charge engine are presented.

A cycle by cycle analysis of engine behavior during the first few cycles of cranking and start-up was performed on a production four-cylinder engine. Experiments were performed to elucidate the effects of initial engine position (rest position after last engine shut-down), first and second cycle fueling, engine temperature, and spark timing on fuel delivery to the cylinder, engine-out Hydrocarbon (EOHC) emissions, and Gross Indicated Mean Effective Pressure (IMEPg). The most important effect of the piston starting position is on the first firing cycle engine rpm, which influences the IMEPg through combustion phasing. Because of the low rpm values for the first cycle, combustion is usually too advanced with typical production engine ignition timing. For both the hot start and the ambient start, the threshold for firing is at an in-cylinder air equivalence ratio (λ) of 1.1.