Diesel Engine Optimisation
As mentioned in the previous article; we have to find solutions for our planet sustainability. Therefore, emissions levels on Diesel applications are defined by legal authorities. Diesel engines are evolving at fast pace since years to meet those emissions levels.
European and United State Non-Road emissions standards for Diesel engines. Source: John Deere
The above chart is plotting six emissions levels for non-Road applications. First level appears mid-1990. The NOx (X-axis) and Particle Matter reduction (Y-axis) from level 1 to nowadays are drastic. The embedded technologies are increasing to achieve those targets.
John Deere 6.8 engine non-Certified (left) and certified Version (right)
John Deere uses a “building-block” approach and adds several features on engine platform to meet higher emissions standards. We will see some of the main improvements from the past 20 years with focus on marine application.
Compliance with emissions thresholds is linked with optimisation of combustion inside the cylinders:
The oldest and widely used technology for point #1 is a French invention by Louis Renault: the turbocharger. This device uses the gas outflow energy to compress air at the intake side. It is an excellent way to increase power and/or reduce fuel consumption.
View of a Turbocharger with gas flow. Source dieselnet.com
The simplest version is called fixed geometry. It is working on a pre-defined engine rotation range. Innovations arise over years:
Due to the Law of thermodynamics; the turbocharger warms the air during compression. But; combustion optimisation requires fresh air. Here comes the aftercooler, intercooler or also charge air cooler. It is all the same: a heat exchanger.
Air flow inside John Deere 6.8l marine aftercooler
The heat exchanger will transfer heat from compressed air to a cooler medium and thus decrease air temperature. Both mediums flow in separate channels and heat is passing through channels wall. In Marine; the coolest medium is generally engine coolant or sea water and channels are made of copper.
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Zoom on John Deere heat exchanger for aftercooler
Once we have fresh charged air; it has to enter inside the cylinders through the cylinder head valves. The old engines have one valve for intake and one for outlet (2 valves per cylinder). The current engine has 4 valves per cylinder: two for intake and two for outlet. The less “resistance” to enter the cylinder the better the efficiency. Some sport cars even have 5 valves to increase performance. The engine has a better “breathing”.
Ferrari F50 with 5 valves per Cylinder engine. Source largus.fr
The important innovation for point #2 and #3 is the Common-Rail. This innovation replaces the “old” mechanical injection pump to increase Diesel pressure and control during injection.
Common Rail system with ECU. Source NPS Yachting CAD Database – John Deere
The pump on the left side is generating a very high pressure but it is not in charge of injection timing. The Diesel under high pressure is buffered inside the rail. It is a “simple” steel tube with thick wall. All injectors are connected to the “common rail” and electronically governed by the Engine Control Unit (ECU, on the right background). The ECU is gathering data from several sensors and use injection map to define parameters such as: pre-injection, quantity or timing.
What do we get when use all these technologies for a marine engine?
Powerful 9.0l John Deere marine engine Side 1. Source John Deere
The aftercooler/intercooler is at the top-right hand side. We can see the main heat exchanger for engine coolant at the front of the engine.
Powerful 9.0l John Deere marine engine Side 2. Source John Deere
The common-rail and high-pressure fuel lines are on top engine side. This engine version is called 6090ASFM85 and reaches IMO Tier II and EPA Tier III emissions compliances
Author: Olivier Krafft - Business Manager at NPS Yachting