Powertrain Systems for Net-Zero Transport

Institution of Mechanical Engineers (IMe, Institution of Mechanical Engineers (IMe

• Publisher: CRC Press
• Year: 2021
• ISBN:
  9781000552072
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Power Resources
• Index: Technology & Engineering

The transport sector continues to shift towards alternative powertrains, particularly with the UK Government's announcement to end the sale of petrol and diesel passenger cars by 2030 and increasing support for alternatives. Despite this announcement, the internal combustion continues to play a significant role both in the passenger car market through the use of hybrids and sustainable low carbon fuels, as well as a key role in other sectors such as heavy-duty vehicles and off-highway applications across the globe.

Building on the industry-leading IC Engines conference, the 2021 Powertrain Systems for Net-Zero Transport conference (7-8 December 2021, London, UK) focussed on the internal combustion engine's role in Net-Zero transport as well as covered developments in the wide range of propulsion systems available (electric, fuel cell, sustainable fuels etc) and their associated powertrains. To achieve the net-zero transport across the globe, the life-cycle analysis of future powertrain and energy was also discussed.

Powertrain Systems for Net-Zero Transport provided a forum for engine, fuels, e-machine, fuel cell and powertrain experts to look closely at developments in powertrain technology required, to meet the demands of the net-zero future and global competition in all sectors of the road transportation, off-highway and stationary power industries.

Session 1: IC Engines for light-duty vehicles

Combustion sensitivity to charge motion in a dilute jet ignition engine

M.P. Bunce¹^,², A. Cairns², S.K.P. Subramanyam¹, N.D. Peters¹, H.R. Blaxill¹

¹MAHLE Powertrain LLC, USA

²University of Nottingham, UK

DOI: 10.1201/9781003219217-1

ABSTRACT

Though there are multiple viable powertrain options available for the automotive sector, those that contain internal combustion engines will continue to account for the majority of global sales for the next several decades. It is therefore imperative to continue the pursuit of novel combustion concepts that produce efficiency levels significantly higher than those of current engines. Introducing high levels of dilution in spark ignited (SI) engines has consistently proven to produce an efficiency benefit compared to conventional stoichiometric engine operation. However, this combustion mode can present challenges for the ignition system. Pre-chamber jet ignition enables stable, highly dilute combustion by both increasing the ignition energy present in the system and distributing it throughout the combustion chamber. Previous work by the authors have shown that jet ignition produces 15-25% increases in thermal efficiency over baseline SI engines with only relatively minor changes to engine architecture.

Lean combustion in general and jet ignition in particular represent fundamentally different engine operating modes compared to those of conventional stoichiometric SI engines. Therefore, there are some system sensitivities not present in stoichiometric engines that must be investigated in order to fully optimize the jet ignition system. Differing types and magnitudes of charge motion are incorporated in SI engines to aid with mixture preparation but the influence of charge motion over lean combustion performance, particularly in jet ignition engines, is less well understood. This study analyzes the impact that charge motion has on both pre-chamber and main chamber combustion. A 1.5L 3-cylinder gasoline engine is outfitted with multiple intake port configurations producing varying magnitudes and types of charge motion. Pre-chamber and main chamber combustion stability and other burn parameter responses are analyzed at part-load conditions. The results show that there is combustion sensitivity to charge motion, resulting in >1 percentage point spread in peak thermal efficiency for the configurations tested, and that this sensitivity manifests most significantly under low ignitability conditions such as heavy dilution. These results provide guidance for future system optimization of jet ignition engines.

1 Introduction

1.1 Background

The perpetual desire to conserve fuel is being coupled with an increasing modern awareness of the deleterious environmental impact of tailpipe emissions from the transportation sector. In response, increasingly stringent global legislation of greenhouse gas emissions will require a step change in internal combustion engine (ICE) efficiency. A method being increasingly explored to accomplish this goal is dilute gasoline combustion [1-8]. The major limitation in developing dilute combustion systems is the less favorable ignition quality of the mixture. This has necessitated the development of higher energy ignition sources [9,10]. A pre-chamber jet igniter application is one such technology, having been researched extensively [11-15]. Pre-chamber combustion concepts have demonstrated the potential for stable main chamber combustion at higher levels of dilution than are allowable in typical SI engines [16].

With a pre-chamber combustor, products from the combustion event inside of the pre-chamber are pushed into the main combustion chamber through a nozzle, which subsequently ignite the main chamber contents. This creates a stronger, more distributed ignition source within the main combustion chamber than would be provided by a standard single-point spark plug. Active pre-chamber concepts contain an auxiliary fueling source in the pre-chamber, enabling de-coupled control over air-fuel ratio in each chamber. This allows the highly reactive jets from a conventional near-stoichiometric combustion event in the pre-chamber to serve as the ignition source for an homogeneous ultra-lean main chamber. MAHLE Jet Ignition^® (MJI) is an auxiliary fueled pre-chamber concept that has been under development for several years [17-19]. MJI is designed to be a low-cost, practical ultra-lean combustion enabling technology. A rendering of pre-chamber placement in a typical cylinder head is shown in Figure 1.

Figure 1. CAD model rendering of a partial cutaway of the pre-chamber assembly in a cylinder head.

Jet ignition concepts generally and MJI specifically possess numerous parameters than can be optimized in order to increase BTE, minimize engine-out emissions, or aid practical engine operation. While many of these parameters have been studied extensively by the authors [2] and others [5,12,14], one parameter for which there is minimal published data on its effect on jet ignition combustion is charge motion.

Charge motion in SI engines is typically used to drive or enhance mixture preparation in the cylinder. With the advent of DI SI engines, the role of charge motion in mixture preparation has become especially critical to ensuring successful combustion and low emissions. The pervasive type of charge motion used in SI engines is tumble, which typically interacts with the bulk of the injector spray. Tumble requires certain length scales and tends to degrade as the piston nears top-dead center (TDC) [20-22], though this effect is highly dependent on combustion chamber geometry, especially compression ratio and stroke-to-bore ratio. It devolves into a general non-ordered turbulent kinetic energy (TKE) with high velocity but no uniform flow field. As such tumble motion tends to not contribute strongly to combustion in and of itself, but high levels of TKE present during the combustion process can increase turbulent flame speed, thereby increasing combustion burn rate. This effect is particularly useful for lean engines, as it helps compensate for the reduction in laminar flame speed inherent in the colder lean combustion environment. High levels of turbulence can, however, have the detrimental effect of stretching the spark kernel, resulting in misfires, and also increase in-cylinder heat loss.

Swirl motion is generally not purposefully used in production SI engines as it provides little mixture preparation benefit. It does not degrade near TDC to nearly the same extent as tumble and therefore it is a potentially useful form of charge motion for lean combustion concepts as it exists during the combustion process. Literature [23-25] and previous simulations performed by MAHLE Powertrain have shown contradictory effects of swirl on lean combustion.

Quader (et al) demonstrated that charge motion has a competing influence on kernel formation and flame front propagation in homogeneous lean combustion SI engines [3]. Hi...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Organising Committee
• Session 1: IC Engines for light-duty vehicles
• Session 2: IC Engines for heavy-duty and off-highway
• Session 3: Engines with sustainable fuels (e.g hydrogen, e-fuels, biomethane)
• Session 4: Simulation, modelling and experimental techniques
• Session 5: Real-world Driving Emission (RDE) and emissions analysis
• Session 6: Real-world Driving Emission (RDE) and emissions control systems
• Session 7: Powertrain development systems and analysis
• Session 8: Powertrain development systems for hybrid electric vehicle
• Author index