Psychoacoustic evaluation of internal combustion engine noises

When buying a car, the acoustic impression of quality of a vehicle drive train is becoming more and more relevant. The perceived sound quality of the engine unit plays a key role here. Due to the nature of individual background noises, that sound quality is negatively influenced. These noise components, which are perceived as unpleasant, need to be further reduced in the course of vehicle development with the identification and evaluation of disruptive noise components in the overall engine noise being a prerequisite for effective acoustics optimization. In particular, the pulsed ticker noise is classified as particularly annoying in Otto DI engines, which is why this article aims to analyze and evaluate the ticking noise components from the overall noise. For this purpose, an empirical formula was developed which can classify the ticking noise components in terms of their intensity. This is purely perception-based and consists of the impulsiveness, the loudness and the sharpness of the overall engine noise. As with other psychoacoustic evaluation scales, the rating was made from 1 (very ticking) to 10 (not ticking). The ticker noise evaluation formula was then verified on the basis of hearing tests with the help of a jury of experts. According to this, it can be predicted precisely in which engine map areas the ticker noise undermines the pleasantness of the overall engine noise.

Operation of a turbine-compound free-piston linear alternator

A free-piston linear-alternator combined with combustion chambers has been examined in many studies. However, only simplified thermodynamic and mechanical models were developed to mimic the actual behavior of the free-piston engine. The purpose of this study is to establish a fully dynamic model that can calculate the energy transformation under the operation of the free-piston engine. The Matlab/Simulink® model uses non-constant-volume combustion event, the piston transient dynamics, flow, heat losses, and thermodynamics as bridges to connect control volumes. The model successfully captured the behavior and measurements of a GS-34 free-piston engine, based on a thermodynamic calculation calibrated with experimental data. The resulting model is used for a series of parametric studies to understand the very complex system behavior, including low load operation. Operation parameters (injection timing and bounce chamber mass) are optimized to generate the engine map for different alternator sizes. At the end, the advantages of the opposed free-piston engine with a linear alternator are presented through the energy analysis.

Research and Development of Self-Contained Water Injection Systems

Reducing fuel consumption and thus CO2 emissions is one of the most urgent tasks of current research in the field of internal combustion engines. Water Injection has proven its benefits to increase power or optimize fuel consumption of passenger cars. This technology enables knock mitigation to either increase the engine power output or raise the compression ratio and efficiency while enabling λ = 1 operation in the complete engine map to meet future emission targets. Current systems have limited container capacity. It is necessary to refill the water tank regularly. This also means that we cannot get the benefits of an engine with a higher compression ratio. For this reason, the self-contained system was investigated. This article is a methodology for finding the right design of a self-contained water injection system, but also a vehicle test that proves the function.

Evaluation of a novel strategy, based in Coolant Flow Rate Control, for avoiding Knock in a SI engine

An experimental study is carried out for investigating the possibility to limit knock occurrence on a SI engine by proper engine thermal management. The control of the wall temperature is realized by means of an electrically driven water pump. The coolant flow rate can be varied regardless of the engine speed. Preliminarily, an experimental campaign aimed at evaluating the effects of the coolant flow rate on the in-cylinder pressure fluctuations, under steady state engine operation, namely WOT@1500 rpm, is presented. In the experiments, the spark advance and the equivalence ratio are controlled by the ECU according to the production engine map and the coolant flow rate is varied from 1500 up to 4500 dm3/h. In a subsequent set of tests, a variation on spark advance is operated and, for each value of the spark advance, different coolant flow rates are enforced with the aim of evaluating the possibility to increase the spark advance as close as possible to the maximum brake torque condition and of mitigating knock occurrence with increased coolant flow rates. The benefits in terms of fuel economy and increase engine performance, in comparison to the traditional approaches for knock mitigation, are evaluated.

A study on the high pressure EGR transport and application to the dispersion among cylinders in automotive engines

The objective of this study is to explore the limits of a one-dimensional model to predict the movement and mixing of the air and exhaust gases recirculation (EGR) flows in compact intake manifolds of recent automotive engines. In particular, the high pressure EGR loop configuration is evaluated in this study from the perspective of the EGR dispersion among cylinders. The experimental work includes the use of a fast CO2 tracking system that provides crank-angle resolved results in six locations of the intake manifold together with the acquisition of the time-averaged CO2 concentration in all the intake pipes (eight locations) to evaluate the EGR dispersion empirically. A specific system was developed to inject the EGR in three locations of the intake manifold in a flexible way to modify the dispersion. Up to 29 engine running conditions defined by engine speed, engine torque and EGR rate, spanning the entire engine map, including full load operation, were evaluated. A one-dimensional engine model was built to detect the limits in reproducing the EGR transport in the intake manifold and quantify the accuracy when predicting the dispersion among cylinders. The study concludes that the predicted EGR rate in the cylinders may differ up to 75% from the experimental measurement at low engine averaged EGR rate. The model prediction improves to differences lower than 40% in EGR rate per cylinder if the engine operating points with an EGR rate lower than 10% are excluded. In this situation, 80% of the predicted in-cylinder EGR rates have differences lower than 25% when compared to experiments.

Efficient light-duty engine using turbulent jet ignition of lean methane mixtures

Diesel engines use diffusion-controlled combustion of a high-reactivity fuel and offer high efficiencies because they combine lean combustion with a high compression ratio. For low-reactivity fuels such as gasoline or natural gas, premixed combustion is used, which leads to lower efficiency levels as usually stoichiometric combustion is combined with lower compression ratios. Trying to apply diesel-like process parameters to low-reactivity fuels inevitably leads to problems with classical spark ignition systems as they are not able to establish robust flame propagation for such hard-to-ignite conditions. One possibility to enable fast combustion for diluted mixtures at high pressure levels is to establish ignition in a prechamber and ignite the charge of the main combustion chamber using the turbulent jets exiting the prechamber. In this study, the experimental results of a prechamber-equipped four-cylinder natural gas engine with 2 L displacement are discussed in detail. In the majority of the engine map, auxiliary fueling is used in the prechamber and a global air–fuel equivalence ratio λ is set to 1.7. At full load, a λ of 1.5 is applied without auxiliary prechamber fueling. The experiments show that such a setup is able to achieve brake efficiency levels of above 45% while maintaining peak brake mean effective pressure levels above 20 bar. At high load conditions, cylinder pressure levels at ignition timing achieve more than 80 bar and cylinder peak pressures of around 180 bars occur. The technology proved to enable robust and very fast combustion at comparably low NOx levels. A remaining challenge for the on-road use of such a technology is the reduction of the methane emissions at lean conditions.

A Novel Air and EGR Emulation Facility for the Optimisation of the Powertrain Architecture

In this work, an external air and EGR emulation facility has been designed that can replicate a wide range of boosting and EGR delivery systems to a multi-cylinder engine platform. The facility works by removing the incumbent air path and replacing it with externally boosted fresh air that is conditioned using a transient flow and temperature controller. The facility also recycles the actual exhaust gases from the engine whilst removing the constraints of required pressure differences to drive this flow. The resulting system is able to control the boundary conditions of intake air flow - pressure and temperature, engine back-pressure and EGR flow rate independently. Three testing approaches have been described that allow to obtain valuable data across a wide range of the engine map (based on an example of a 1.0L direct injection gasoline engine) also beyond its typical hardware related limits. The facility is designed to be used as part of an engine design optimisation process. The facility generates data of the engine combustion system independently of the associated air path subsystems and excites the boundary conditions beyond those that would be expected from a specific air path design. The data is then used to populate 1D engine models which can be confidently used to predict the performance of a specific air path hardware combination and control strategy.

Diesel Engine Characterization and Performance Scaling via Brake Specific Fuel Consumption Map Dimensional Analysis

The goal of this work is to develop easily generalized models of heavy duty truck engine maps that allow for approximate comparisons of engine performance, thus enabling fuel efficient matching of engines to a set of corresponding loads and routes. This is achieved by applying dimensional analysis to create a uniformly applicable, dimensionless Brake Specific Fuel Consumption (BSFC) map that fits the behavior of a wide range of diesel engines. A commonality between maps was found to occur when engine data is scaled by specific dimensional parameters that target data consistency among the primary operating points across engines. This common map highlights observable trends in engine performance based on the influence of these same parameters being scaled across engines. The resulting dimensionless engine map fits the minimum BSFC regions of four diesel engines to within 2.5 percent.