Investigating Fuel Condensation Processes in Low Temperature Combustion Engines

Condensation of gaseous fuel is investigated in a low temperature combustion engine fueled with double direct-injected diesel and premixed gasoline at two load conditions. Possible condensation is examined by considering real gas effects with the Peng-Robinson equation of state and assuming thermodynamic equilibrium of the two fuels. The simulations show that three representative condensation events are observed. The first two condensations are found in the spray some time after the two direct injections, when the evaporative cooling reduces the local temperature until phase separation occurs. The third condensation event occurs during the late stages of the expansion stroke, during which the continuous expansion sends the local fluid into the two-phase region again. Condensation was not found to greatly affect global parameters, such as the average cylinder pressure and temperature mainly because, before the main combustion event, the condensed phase was converted back to the vapor phase due to compression and/or first stage heat release. However, condensed fuel is shown to affect the emission predictions, including engine-out particulate matter and unburned hydrocarbons.

Dynamic Identification of Thermodynamic Parameters for Turbocharger Compressor Models

A novel experimental procedure is presented which allows simultaneous identification of heat and work transfer parameters for turbocharger compressor models. The method introduces a thermally transient condition and uses temperature measurements to extract the adiabatic efficiency and internal convective heat transfer coefficient simultaneously, thus capturing the aerodynamic and thermal performance. The procedure has been implemented both in simulation and experimentally on a typical turbocharger gas stand facility. Under ideal conditions, the new identification predicted adiabatic efficiency to within 1%point and heat transfer coefficient to within 1%. A sensitivity study subsequently showed that the method is particularly sensitive to the assumptions of heat transfer distribution pre and post compression. If 20% of the internal area of the compressor housing is exposed to the low pressure intake gas, and this is not correctly assumed in the identification process, errors of 7–15%points were observed for compressor efficiency. This distribution in heat transfer also affected the accuracy of heat transfer coefficient which increased to 20%. Thermocouple sensors affect the transient temperature measurements and in order to maintain efficiency errors below 1%, probes with diameter of less than 1.5mm should be used. Experimentally, the method was shown to reduce the adiabatic efficiency error at 90krpm and 110krpm compared to industry standard approach from 6% to 3%. However at low speeds, where temperature differences during the identification are small, the method showed much larger errors.

The Evolution of Diesel Engine Performance Prediction

Thermodynamic system performance modeling has become an integral part of the engine development process. The modeling tools used for this type of analysis have evolved from fairly simple calculations of limited scope into detailed simulations with ever-increasing complexity. These analytical tools are based on the combination of basic concepts, physical phenomena and experimental correlations. As with other categories of analysis, their evolution has also been closely coupled with the advances in computer technology. This document provides a historic view of thermodynamic system simulation and revisits some of the developments in modeling techniques, engine measurements, data acquisition systems and computer hardware that have contributed to the understanding of engine performance prediction.

Predictions of Flow Separation at the Valve-Seat for Steady-State Port-Flow Simulation

Steady-state port-flow simulations with static valve lift are often utilized to optimize the performance of intake system of an internal combustion engine. Generally, increase in valve lift results in higher mass flow rate through the valve. But in certain cases, mass flow rate can actually decrease with increased valve lift, caused by separation of turbulent flow at the valve-seat. Prediction of this phenomenon using computational fluid dynamics (CFD) models is not trivial. It is found that the computational mesh significantly influences the simulation results. A series of steady-state port flow simulation are carried out using a commercial CFD code. Several mesh topologies are applied for the simulations. The predicted results are compared with available experimental data from flow bench measurements. It is found that the flow separation and reduction in mass flow rate with increased valve lift can be predicted when high mesh density is used in the proximity of the valve seat and the walls of the intake port. Higher mesh density also gives better predictions of mass flow rate compared to the experiments, but only for high valve lifts. For low valve lifts, the error in predicted flow rate is close to 13%.

Effects of Multi-Grade Oils in Modeling Non-Newtonian Rheology Between Piston and Cylinder Surfaces in Engine Initial Start Up Conditions

This paper presents the results of a transient analysis of hydrodynamic lubrication between piston and cylinder surfaces in engine Initial startup conditions with a Non Newtonian lubricant under oscillatory motion. Effects of different multi-grade oil viscosities are also investigated in the simulation. The time dependent Reynolds equations use a Maxwell type model to analyze fluid rheology. A perturbation scheme is used to derive coupled non linear partial differential equations to obtain the fluid velocity. The oil film profile is predicted by solving the two-dimensional Reynolds equations using the finite difference computational method. The piston velocities in engine secondary motion are adjusted by using fourth order Runge-Kutta technique. Using different oil viscosities, the effect of viscoelasticity on lubricant velocity and pressure fields is examined and the influence of film thickness on lubricant characteristics is investigated. Numerical simulations show that piston eccentricities and film thickness profiles vary under different multi grade oils at engine start up conditions.

Fast Measurement of Soot by In-Situ LII on a Production Engine

The contribution of transient emissions to total emissions is becoming more important in view of the improvement of steady state emissions and after-treatment systems. For a critical pollutant, namely soot, there is no commercially available measurement system able to measure sufficiently fast on production engines. This paper presents a measurement setup based on in-situ Laser Induced Incandescence (LII) allowing high speed, frequent soot measurements in a production engine. The setup consists of a pulsed laser system, a fast optical detector and a special, compact designed in-situ optical LII probe which makes it possible to change the measurement location easily. System speed is assessed among other approaches, by using eleven well defined soot steps obtained by injection pulses under controlled conditions on a highly dynamic test bench. The effect of these pulses for a production four-cylinder 2 lt. Euro 5 Diesel engine is measured at three different positions (at tailpipe, downstream of the turbine and in exhaust manifold). The features of LII intensity are extracted by principle component analyses (PCA) and compared with a fast and commercially available device (AVL Opacimeter) at last. The results show that the measurements with the proposed setup are able to detect all peaks in contrast to the commercially available device.

Nano Napier Steel Second Ring for SI Applications

Piston top compression rings utilized in North American Spark Ignition (SI) passenger car and light truck engines have undergone a significant migration driven by desire to reduce axial height, mass, radial thickness, wear, incidence of risk of foundry defects and to enable utilization of a consistent, global material independent of manufacturing location. Second rings utilized in similar applications are now in the earlier stages of a similar migration. This paper will present product development of an innovative steel second ring including engine testing (blowby, and lube oil consumption via radiometric tracer method), supplemented by simulation modeling utilizing MIT code, including several more conventional ring cross sectional alternatives.

A Study on the Effect of Pressure Balance Between the Second and Third Land of a Piston on Engine Oil Consumption

Engine oil consumption causes particulate matter, poisoning of catalysts, abnormal combustion like pre-ignition in a gasoline engine, and an increase in customer’s running cost. Oil consumption, therefore, must be reduced. It is well known that pressure at a piston second land sometimes becomes larger than the cylinder pressure in the latter half of the expansion stroke. Larger pressure at the second land causes an increase in engine oil consumption. For reducing the second land pressure, increasing volume of a piston second land is one of design schemes. Pressure at a piston second land is calculated in piston design stage. In the calculation, pressure at a piston third land is assumed as same as pressure at the crankcase. This study aimed the effect of volume of the third land of a piston on engine oil consumption. The third and the second lands pressure were measured using an optical fiber type pressure sensor. It was found that the third land pressure showed a quite different trend from the crankcase pressure. It was also found that the pressure balance between the second land and the third land affected engine oil consumption. It was suggested that the third land pressure should be considered in the calculation for lands pressure of a piston and further investigation on third land design for reducing engine oil consumption may be required.

Advanced Numerical Approach to Simulate GDI Sprays Under Engine-Like Conditions

Gasoline direct-injection (GDI) engines provide both higher engine power and better fuel efficiency than port-injection gasoline engines. However, they emit more particulate matter (PM) than the latter engines. Fuel stuck on walls of pistons and combustion chambers forms a high-density region of fuel in the air/fuel mixture, which becomes a source of PM. To decrease the amount of PM, fuel injectors with short length of spray-penetration are required. A fuel-spray simulation was previously developed; that is, the air/fuel-mixture simulation was integrated with the liquid-column-breakup simulation. The developed fuel-spray simulation was used to optimize the nozzle shapes of fuel injectors for gasoline direct-injection engines. In the present study, the factors that influence spray-penetration length were identified by the numerical simulation. The simulation results were validated by comparing the simulated spray-penetration length with the measured ones and revealing good agreement between them. Angle α was defined as that formed between the direction of flow entering the nozzle inlet and the direction of flow leaving the nozzle outlet; in other words, a indicates a change of flow direction. It was found that α and spray-penetration length was closely related. Velocity that are accelerated with a were studied, and it was found that the velocity within a plane perpendicular to the center axis of the nozzle increases with increasing α.

Computational Analysis in Test Cell Design With Application in Emissions Control

Computer-Aided Engineering (CAE) tools have been widely used in the design of automotive components and systems. Methods, procedures and measurables for analyses involving Internal Combustion Engine (ICE) components are well-defined and well developed. Comparatively, significantly less attention has been paid to the design and analysis of test cells. Better designed test cells will lead to increased test cell availability and thus also increases engine performance test opportunities. This trend was observed in Cummins Inc. where CAE-guided test cell designs improved test-cell availability and rate of engine development. Here, improved conversion efficiencies in test cell Selective Catalyst Reduction (SCR) modules were predicted using Computational Fluid Dynamics (CFD) tools, and validated against data collected from the test cells. The resultant improvements resulted in dramatic increases in test cell up-time. This paper documents how CAE tools commonly used in engine design were successfully expanded to aid the design of Cummins Inc. test cells. It presents the CFD methods that were used in this analysis, compares CFD predictions to actual conversion efficiencies in the SCR module, and also proposes a set of analysis tasks and methods that can be applied to improve test cell design and performance in the future.