Would a diesel-electric hybrid be better mpg than gas-electric hybrid

[Topher925]

A modern engine is already a pretty complex system, I don't see this adds much.

You can't even compare the complexity of a regular modern engine to that of an HCCI engine the complexity is so great. With modern engines you really only need to control spark timing, fuel flow, and throttle, along with some ancillary devices like cooling. With HCCI, you need to control EVERYTHING. Its not like a regular engine where you have fixed valve timing. The valves need to be controlled independently and with a very high degree of accuracy which means high speed/pressure hydraulics instead of cam shafts. Temperature sensors and pressure transducers are required all over the place and not to mention the computer hardware to run all this.

 

[xxChrisxx]

A modern engine is already a pretty complex system, I don't see this adds much.
I can see that GM probably doesn't want to launch a diesel in the US but Merc and VW had prototypes 3-4 years ago.
Interestingly Merc see it as a way of upping the MPG and reducing the CO2 of their big sedans so they don't get slammed by higher taxes in europe. So it might be that you don't want to do too much too soon since the regulatory limits will just chase you down.

VW are very happy selling small turbo diesels (more than 50% of new small cars in europe are oil burners - and a big chunk of them are VW) they see the future of this technology that it can burn pretty much anything without modification. That obviously saves them tooling between different markets but I don't think individual consumers are going to switch between ethanol, biodeisel, vegatable oil at the pumps from day-day.

HCCI isn't a diesel per se (although I think you may be able to use diesel in them). And the control system for HCCI isn't even in the same league as any current engine.

HCCI is putting requirements for control on things that currently we can't. E.g. Exact cylinder temperature on a cycle by cycle basis. The bold bit is what makes this such a task.

It can (and will) be done, it just needs two things time and money.