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GM took a different path on their diesel engine for the Cruze. They went with a single VNT turbocharger. In the cutaway of the turbo, you can see the vanes that rotate which make it a variable nozzle turbine. Check out the beefy pistons required by diesels. The side skirts are much bigger to handle the greater cylinder pressures and side-loading as compared to gasoline engines.
Here is something interesting on the GM diesel… there’s a butterfly valve on one of the two intake ports for each cylinder. My first guess is that it helps to promote swirl in the cylinder for better mixing under lower load conditions. Or it may be for increasing exhaust temperatures to help with the emissions catalysts; the catalysts have a minimum temperature required to be effective. By choking off air, the air-fuel ratio becomes richer and closer to stoichiometric (diesels pretty much always run with a lean A/F ratio). So, the exhaust temperatures go up. Or I could be completely wrong on both counts.
GM of course has this big Duramax diesel. You can see the turbo is mounted in the V on the back half of the engine. The turbo itself also has a VNT as do many, if not most, diesel engines today. There is a lot going on in this picture, so bear with me. Way down low is the single cam (I’m so used to saying ‘cams’, it’s weird for me to say ‘cam’). It of course uses a push rod connected to a rocker arm to actuate the valves. Under the exposed cylinders, you can see a heat exchanger cut in half. I’m guessing that’s an EGR cooler; the exhaust gas needs to be cooled down to most effectively reduce NOx by reducing combustion temperatures. Looking back at the turbo, there’s no straight shot for air to get into the compressor due to the turbo being buried on the back half of the engine. So, you can see an intake tube is attached that makes a 90 degree turn off the compressor inlet and bends upwards in the 2 O’clock direction. For sure some CFD work had to be performed to keep from negatively impacting compressor performance as ideally you would only want a straight shot into the compressor. Next to the turbo on top of the other cylinder bank looks to be another EGR cooler. You can see the pipe going to the cooler from the exhaust pipe going between the exhaust manifold and turbo. Of course, there’s a bellows joint on the pipe going to what I think is the EGR valve connected to the EGR cooler. There is definitely a lot of emissions stuff on the modern diesel engine which makes them so clean. You never see the black smoke of the old school diesels from a modern diesel.
What’s that? A throttle body on a diesel? Yup, I’m pretty sure that’s used to choke the intake air to bring up the exhaust temperatures to keep the emissions catalysts and DPF up to temperature to operate correctly. Down in the V in front of the turbo is some other heat exchanger and I have no clue what it’s used for. Nor that tube with the bellow positioned above it. It’s probably more emissions related stuff.
GM’s turbocharged 1.4L gasoline engine that comes in the Cruze. Nothing too exciting here, I just wanted to show the common integrated exhaust manifold and turbine housing. I guess another common theme with the new breed of small turbocharged 4-cylinder engines is that they have the turbo mounted on the backside of the engine up against the rear firewall of the engine bay. Therefore, most of them have this long elephant trunk of a compressor inlet. The turbos on the VW/Audi 1.8 and 2.0 gas engines have had this type of design for a long time.
