Towards zero emission engines through the adoption of combustion lead engine design realised through a split cycle topology

Khalid, F.; Harvey, Simon; Morgan, Robert; Vogiatzaki, Konstantina; Atkins, Andrew; Mason, David; Heikal, M.R.

Abstract

Although electrification is expected to dominate city transportation, chemically fuelled propulsion systems will remain the technology of choice for intercity freight transportation. This is due to the high journey energy requirements that cannot be covered by batteries, even at the predicted future power density levels. Tailpipe emissions will still need to approach zero for the vehicle to enter emissions-controlled areas such as the centre of major cities. It is well known that to achieve zero emissions, conditions in the combustion chamber must be lean enough to avoid particulate matter formation and cool enough to avoid the formation of NOx. Many concepts have been proposed with varying degrees of success. Issues, such as high reaction rates resulting in knock, high cycle-cycle variability, misfire and high pumping work have been reported. The palliatives required to address these issues have inevitably compromised the proposed solutions, resulting in complexity, poor power density and low thermal efficiency.
A common feature of most solutions proposed for achieving zero emissions combustion is the adoption of conventional engine architectures. In this paper, the potential of a new combustion concept is explored that has been derived by taking an alternate design approach where the ideal thermodynamic conditions in the chamber to achieve zero emissions at maximum thermodynamic efficiency are first defined. Following, having defined the ideal thermodynamic conditions, a novel fuel and hardware con-figuration to achieve these conditions is suggested instead of simply adapting conventional architectures.
The paper is structured as following: A fundamental kinetic analysis using CHEMKIN is described first in order to define suitable starting conditions for the reaction process considering variables such as temperature, mixture strength (i.e., air-fuel equivalence ratio (φ)) and fuel chemistry. Based on this analysis, suitable operating zones for the combustion system are defined that fulfil the criteria of complete combustion at zero NOx and particulate emissions. One of the main findings of the analysis is that precise control of temperature at the start of combustion was critical to delivering practical zero emissions combustion. A split cycle engine, where the compression stroke is performed in a separate cylinder and the charge air is ‘injected’ with the fuel into the combustion chamber, is presented as optimum hardware configuration that can give the necessary control of the initial conditions and so avoid the formation of emissions.

• Presentation Conference Type: Conference Paper (unpublished)
• Conference Name: Thermo and fluid dynamic processes in direct injection engines (THIESEL) conference
• Start Date: Sep 11, 2018
• End Date: Sep 14, 2018
• Deposit Date: Dec 14, 2021
• Public URL: https://uwe-repository.worktribe.com/output/8037395