For a while now, I’ve been planning a tadpole (also known as reverse trike) three-wheel vehicle that would have tandem seating, an enclosed cabin, and would achieve 156+ miles per US gallon on the highway by using a diesel engine.
I’ve even bought a 654 cc twin-cylinder Ruggerini diesel engine for this project. Here’s the problem though.
That diesel will get me in the ballpark of 16-20 hp. While that will be more than enough to achieve cruising speed, 16 hp won’t get me acceptable acceleration, and even 20 hp will be painful. In addition, the driveline will be rather long, due to having the transmission behind the engine (and a fair distance away to avoid fouling the oil filter), and then the rear wheel behind that.
So, my question to you is… should I abandon the diesel route, and go to a 300 cc single-cylinder fuel injected gasoline engine from a scooter (which means CVT)?
The major downsides would be a loss of bottom-end torque, a major loss in efficiency – it would likely struggle to get much past 100 miles per gallon – and a loss of ability to run sustainable biofuels.
On the flipside, vehicle weight (which is not everything when it comes to fuel efficiency – aerodynamics is far more important – but it helps, and it also improves handling and stability, especially because all of the weight is coming out of the rear) is reduced significantly, vehicle length is reduced significantly (making parking lot maneuvering significantly better, especially given that the first prototype will have no reverse gear), assembly is greatly simplified (I don’t really need to worry about the rear section of the vehicle at all, as it can come from the donor scooter, engine cooling is improved (water instead of air, which also means a reasonable way to get cabin heat), and overall cost might be reduced. Oh, and I get 29.5 hp @ 8500 instead of 16 @ 3600 or maybe 20 @ 4000, albeit only 18 ft-lbs @ 6500 instead of 23.6 @ 2400.
Another factor is, if the prototype is successful, I’d like to put it into production, and as much as I hate to admit it, a CVT will be seen as more desirable than a manual for much of the potential target market. And, the cheaper factor helps, too, given that I have a (admittedly pie-in-the-skyish goal) of selling these things for $5000 for a base model. However, a reverse gear may be harder to implement with such a setup…
So, is it worth the loss in economy to get all these benefits? You be the judge, let me know in the comments here or wherever you saw this post, thanks!
small turbo for the diesel?
I could probably get it to make 5-10 psi on a RHB31, the problem is that I don’t have a good way to enrichen the fuel mixture, and it increases cost EVEN MORE (basically, there’d be way too much money into powertrain to even consider building this thing and selling them for $5000, and price is part of how a production version would need to work).
Then again, if I build it as a one-off for myself, the diesel makes sense. As a prototype for a production one, the gasser makes sense.
Decided to go gasoline, it’ll be a cheaper and far easier option in the long run, and the cash from selling the Ruggerini engine I have now wouldn’t hurt.
Well, my thought is to use neither diesel or gas, essentially removing petroleum based issues from the project, which are old technology at this point in history and definitely unsustainable from an environmental viewpoint. Due to the significant advances of electric motors, short charging times, and paper thin photovoltaic cells these days, using such a setup for your trike would send a clear message to the present and upcoming generations that you support ideologies more in step with current and yet developing ideologies. The move away from atmospherically destructive technology is now strong, and an electric solution would position you at the leading edge of a green revolution that has taken hold in affluent cultures on Earth. Consider that if one is to put significant time, effort, and finances into a project, only to find more of the masses moving away from that paradigm, it may result in disappointment. By using modern and sustainable methods, one’s efforts will not be in vain. Okay, such are my brief ideas on your question. Take care!
Steve: Unfortunately, with the current (and near future foreseeable) US generation mix, I’m not convinced that electric is really any more environmentally friendly than an efficient internal combustion drivetrain, and offers some significant drawbacks relating to cost (which I feel is critical to keep low, so that people will actually buy it, without having to rely on government subsidies) and range.
However, my idea isn’t inherently internal combustion. It’ll just be built that way as the prototype, and if I do go into production, the initial production. If and when electrification makes sense, then the design could be relatively easily modified to be electrified, as the basic tenet of the design is a lightweight, extremely streamlined three wheel vehicle, and fuel type isn’t inherent to the concept.